Computing_Informatics Complete Note

LESSON 1

BASIC CONCEPTS

1.1 INTRODUCTION

Let us begin with the word ‘compute’. It means ‘to calculate’. We all are familiar with calculations in

our day to day life. We apply mathematical operations like addition, subtraction, multiplication, etc.

and many other formulae for calculations. Simpler calculations take less time. But complex

calculations take much longer time. Another factor is accuracy in calculations. So man explored with

the idea to develop a machine which can perform this type of arithmetic calculation faster and with

full accuracy. This gave birth to a device or machine called ‘computer’.

The computer we see today is quite different from the one made in the beginning. The number of

applications of a computer has increased, the speed and accuracy of calculation has increased. You

must appreciate the impact of computers in our day to day life. Reservation of tickets in Air Lines and

Railways, payment of telephone and electricity bills, deposits and withdrawals of money from banks,

business data processing, medical diagnosis, weather forecasting, etc. are some of the areas where

computer has become extremely useful.

However, there is one limitation of the computer. Human beings do calculations on their own. But

computer is a dumb machine and it has to be given proper instructions to carry out its calculation.

This is why we should know how a computer works.

1.2 OBJECTIVES

After going through this lesson you will be in a position to

define a computer

identify characteristics of computer

know the origin and evolution of computer

identify capability of computer in terms of speed and accuracy

distinguish computer from human beings and calculator

identify the role of computer

appreciate the evolution of computer through five generations

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1.3 WHAT IS A COMPUTER?

Computer is an electronic device. As mentioned in the introduction it can do arithmetic calculations

faster. But as you will see later it does much more than that. It can be compared to a magic box, which

serves different purpose to different people. For a common man computer is simply a calculator,

which works automatic and quite fast. For a person who knows much about it, computer is a machine

capable of solving problems and manipulating data. It accepts data, processes the data by doing some

mathematical and logical operations and gives us the desired output.

Therefore, we may define computer as a device that transforms data. Data can be anything like marks

obtained by you in various subjects. It can also be name, age, sex, weight, height, etc. of all the

students in your class or income, savings, investments, etc., of a country. Computer can be defined in

terms of its functions. It can i) accept data ii) store data, iii) process data as desired, and iv) retrieve

the stored data as and when required and v) print the result in desired format. You will know more

about these functions as you go through the later lessons.

1.4 CHARACTERISTICS OF COMPUTER

Let us identify the major characteristics of computer. These can be discussed under the headings of

speed, accuracy, diligence, versatility and memory.

1.4.1 Speed

As you know computer can work very fast. It takes only few seconds for calculations that we take

hours to complete. Suppose you are asked to calculate the average monthly income of one thousand

persons in your neighborhood. For this you have to add income from all sources for all persons on a

day to day basis and find out the average for each one of them. How long will it take for you to do

this? One day, two days or one week? Do you know your small computer can finish this work in few

seconds? The weather forecasting that you see every day on TV is the results of compilation and

analysis of huge amount of data on temperature, humidity, pressure, etc. of various places on

computers. It takes few minutes for the computer to process this huge amount of data and give the

result.

You will be surprised to know that computer can perform millions (1,000,000) of instructions and

even more per second. Therefore, we determine the speed of computer in terms of microsecond (10 -6

part of a second) or nano-second (10-9 part of a second). From this you can imagine how fast your

computer performs work.

1.4.2 Accuracy

Suppose some one calculates faster but commits a lot of errors in computing. Such result is useless.

There is another aspect. Suppose you want to divide 15 by 7. You may work out up to 2 decimal

places and say the dividend is 2.14. I may calculate up to 4 decimal places and say that the result is

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2.1428. Some one else may go up to 9 decimal places and say the result is 2.142857143. Hence, in

addition to speed, the computer should have accuracy or correctness in computing.

The degree of accuracy of computer is very high and every calculation is performed with the same

accuracy. The accuracy level is determined on the basis of design of computer. The errors in computer

are due to human and inaccurate data.

1.4.3 Diligence

A computer is free from tiredness, lack of concentration, fatigue, etc. It can work for hours without

creating any error. If millions of calculations are to be performed, a computer will perform every

calculation with the same accuracy. Due to this capability it overpowers human being in routine type

of work.

1.4.4 Versatility

It means the capacity to perform completely different type of work. You may use your computer to

prepare payroll slips. Next moment you may use it for inventory management or to prepare electric

bills.

1.4.5 Power of Remembering

Computer has the power of storing any amount of information or data. Any information can be stored

and recalled as long as you require it, for any numbers of years. It depends entirely upon you how

much data you want to store in a computer and when to lose or retrieve these data.

1,4.6 No IQ

Computer is a dumb machine and it cannot do any work without instruction from the user. It performs

the instructions at tremendous speed and with accuracy. It is you to decide what you want to do and in

what sequence. So a computer cannot take its own decision as you can.

1.4. 7 No Feeling

It does not have feelings or emotion, taste, knowledge and experience. Thus it does not get tired even

after long hours of work. It does not distinguish between users.

1.4.8 Storage

The Computer has an in-built memory where it can store a large amount of data. You can also store

data in secondary storage devices such as floppies, which can be kept outside your computer and can

be carried to other computers.

IN-TEXT QUESTIONS 1

1. What is a computer? Why is it known as data processor?

2. What are the important characteristics of computer?

1.5 HISTORY OF COMPUTER

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History of computer could be traced back to the effort of man to count large numbers. This process of

counting of large numbers generated various systems of numeration like Babylonian system of

numeration, Greek system of numeration, Roman system of numeration and Indian system of

numeration. Out of these the Indian system of numeration has been accepted universally. It is the

basis of modern decimal system of numeration (0, 1, 2, 3, 4, 5, 6, 7, 8, 9). Later you will know how

the computer solves all calculations based on decimal system. But you will be surprised to know that

the computer does not understand the decimal system and uses binary system of numeration for

processing.

We will briefly discuss some of the path-breaking inventions in the field of computing devices.

1.5 .1 Calculating Machines

It took over generations for early man to build mechanical devices for counting large numbers. The

first calculating device called ABACUS was developed by the Egyptian and Chinese people.

The word ABACUS means calculating board. It consisted of sticks in horizontal positions on which

were inserted sets of pebbles. A modern form of ABACUS is given in Fig. 1.2. It has a number of

horizontal bars each having ten beads. Horizontal bars represent units, tens, hundreds, etc.

1.5.2 Napier’s bones

English mathematician John Napier built a mechanical device for the purpose of multiplication in

1617 A D. The device was known as Napier’s bones.

1.5.3 Slide Rule

English mathematician Edmund Gunter developed the slide rule. This machine could perform

operations like addition, subtraction, multiplication, and division. It was widely used in Europe in 16 th

century.

1.5.4 Pascal's Adding and Subtractory Machine

You might have heard the name of Blaise Pascal. He developed a machine at the age of 19 that could

add and subtract. The machine consisted of wheels, gears and cylinders.

1.5.5 Leibniz’s Multiplication and Dividing Machine

The German philosopher and mathematician Gottfried Leibniz built around 1673 a mechanical device

that could both multiply and divide.

1.5.6 Babbage’s Analytical Engine

It was in the year 1823 that a famous English man Charles Babbage built a mechanical machine to do

complex mathematical calculations. It was called difference engine. Later he developed a general-

purpose calculating machine called analytical engine. You should know that Charles Babbage is

called the father of computer.

1.5.7 Mechanical and Electrical Calculator

In the beginning of 19th century the mechanical calculator was developed to perform all sorts of

mathematical calculations. Up to the 1960s it was widely used. Later the rotating part of mechanical

calculator was replaced by electric motor. So it was called the electrical calculator.

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1.5.8 Modern Electronic Calculator

The electronic calculator used in 1960 s was run with electron tubes, which was quite bulky. Later it

was replaced with transistors and as a result the size of calculators became too small.

The modern electronic calculator can compute all kinds of mathematical computations and

mathematical functions. It can also be used to store some data permanently. Some calculators have in-

built programs to perform some complicated calculations.

IN-TEXT QUESTIONS 2

1. What is the first mathematical device built and when was it built?

2. Who is called the father of Computer Technology.

1.6 COMPUTER GENERATIONS

You know that the evolution of computer started from 16th century and resulted in the form that we

see today. The present day computer, however, has also undergone rapid change during the last fifty

years. This period, during which the evolution of computer took place, can be divided into five

distinct phases known as Generations of Computers. Each phase is distinguished from others on the

basis of the type of switching circuits used.

1.6.1 First Generation Computers

First generation computers used Thermion valves. These computers were large in size and writing

programs on them was difficult. Some of the computers of this generation were:

ENIAC: It was the first electronic computer built in 1946 at University of Pennsylvania, USA by

John Eckert and John Mauchy. It was named Electronic Numerical Integrator and Calculator

(ENIAC). The ENIAC was 3050 feet long, weighed 30 tons, contained 18,000 vacuum tubes,

70,000 registers, 10,000 capacitors and required 150,000 watts of electricity. Today your favorite

computer is many times as powerful as ENIAC, still size is very small.

EDVAC: It stands for Electronic Discrete Variable Automatic Computer and was developed in 1950.

The concept of storing data and instructions inside the computer was introduced here. This allowed

much faster operation since the computer had rapid access to both data and instructions. The other

advantages of storing instruction was that computer could do logical decision internally.

Other Important Computers of First Generation

EDSAC: It stands for Electronic Delay Storage Automatic Computer and was developed by M.V.

Wilkes at Cambridge University in 1949.

UNIVAC-1: Ecker and Mauchly produced it in 1951 by Universal Accounting Computer setup.

Limitations of First Generation Computer

Followings are the major drawbacks of First generation computers.

1. The operating speed was quite slow.

2. Power consumption was very high.

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3. It required large space for installation.

4. The programming capability was quite low.

1.6.2 Second Generation Computers

Around 1955 a device called Transistor replaced the bulky electric tubes in the first generation

computer. Transistors are smaller than electric tubes and have higher operating speed. They have no

filament and require no heating. Manufacturing cost was also very low. Thus the size of the computer

got reduced considerably.

It is in the second generation that the concept of Central Processing Unit (CPU), memory,

programming language and input and output units were developed. The programming languages such

as COBOL, FORTRAN were developed during this period. Some of the computers of the Second

Generation were

1. IBM 1620: Its size was smaller as compared to First Generation computers and mostly used for

scientific purpose.

2. IBM 1401: Its size was small to medium and used for business applications.

3. CDC 3600: Its size was large and is used for scientific purposes.

1.6.3 Third Generation Computers

The third generation computers were introduced in 1964. They used Integrated Circuits (ICs). These

ICs are popularly known as Chips. A single IC has many transistors, registers and capacitors built on

a single thin slice of silicon. So it is quite obvious that the size of the computer got further reduced.

Some of the computers developed during this period were IBM-360, ICL-1900, IBM-370, and VAX-

750. Higher level language such as BASIC (Beginners All purpose Symbolic Instruction Code) was

developed during this period.

Computers of this generations were small in size, low cost, large memory and processing speed is

very high.

1.6.4 Fourth Generation Computers

The present day computers that you see today are the fourth generation computers that started around

1975. It uses large scale Integrated Circuits (LSIC) built on a single silicon chip called

microprocessors. Due to the development of microprocessor it is possible to place computer’s central

processing unit (CPU) on single chip. These computers are called microcomputers. Later very large

scale Integrated Circuits (VLSIC) replaced LSICs.

Thus the computer which was occupying a very large room in earlier days can now be placed on a

table. The personal computer (PC) that you see in your school is a Fourth Generation Computer.

1.6.5 Fifth Generation Computer

The computers of 1990s are said to be Fifth Generation computers. The speed is extremely high in

fifth generation computer. Apart from this it can perform parallel processing. The concept of

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Artificial intelligence has been introduced to allow the computer to take its own decision. It is still in a

developmental stage.

1.7 TYPES OF COMPUTERS

Now let us discuss the varieties of computers that we see today. Although they belong to the fifth

generation they can be divided into different categories depending upon the size, efficiency, memory

and number of users. Broadly they can be divided it to the following categories.

1. Microcomputer: Microcomputer is at the lowest end of the computer range in terms of speed and

storage capacity. Its CPU is a microprocessor. The first microcomputers were built of 8-bit

microprocessor chips. The most common application of personal computers (PC) is in this

category. The PC supports a number of input and output devices. An improvement of 8-bit chip is

16-bit and 32-bit chips. Examples of microcomputer are IBM PC, PC-AT .

2. Mini Computer: This is designed to support more than one user at a time. It possesses large

storage capacity and operates at a higher speed. The mini computer is used in multi-user system in

which various users can work at the same time. This type of computer is generally used for

processing large volume of data in an organisation. They are also used as servers in Local Area

Networks (LAN).

3. Mainframes: These types of computers are generally 32-bit microprocessors. They operate at

very high speed, have very large storage capacity and can handle the work load of many users. They

are generally used in centralised databases. They are also used as controlling nodes in Wide Area

Networks (WAN). Example of mainframes are DEC, ICL and IBM 3000 series.

4. Supercomputer: They are the fastest and most expensive machines. They have high processing

speed compared to other computers. They have also multiprocessing technique. One of the ways in

which supercomputers are built is by interconnecting hundreds of microprocessors. Supercomputers

are mainly being used for whether forecasting, biomedical research, remote sensing, aircraft design

and other areas of science and technology. Examples of supercomputers are CRAY YMP, CRAY2,

NEC SX-3, CRAY XMP and PARAM from India.

IN-TEXT QUESTIONS 3

1. Into how many generations the evolution of computer is divided?

2. What is VLSIC?

3. The personal computer that you see today is in which generation of computer?

1.8 WHAT YOU HAVE LEARNT

In this lesson we have discussed about the major characteristics of computer. The speed, accuracy,

memory and versatility are some of the features associated with a computer. But the computer that we

see today has not developed over night. It has taken centuries of human effort to see the computer in

its present form today. There are five generations of computer. Over these generations the physical

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size of computer has decreased, but on the other hand the processing speed of computer has improved

tremendously. We also discussed about the varieties of computers available today.

1.9 TERMINAL QUESTIONS

1. Why is computer known as data processor?

2. Explain in brief the various generations in computer technology?

3. Write a short note on Fifth Generation of computer. What makes it different from Fourth

generation computer?

4. Why did the size of computer get reduced in third generation computer?

5. Give short notes on the following:

(a) Versatility (b) Storage (c) Slide Rule (d) Babbage’s Analytical Engine

6. Distinguish between Microcomputer and Mainframe computer.

1.10 FEEDBACK TO IN-TEXT QUESTIONS

IN-TEXT QUESTIONS 1

1. A computer is an electronic device, which is used to accept, store, retrieve and process the

data. It is called as data processor because it is mainly used for processing data for producing

meaningful information.

2. The characteristics of computer are speed, accuracy, diligence, versatility and storage.

IN-TEXT QUESTIONS 2

1. Analytical engine, 1823.

2. Charles Babbage

IN-TEXT qUESTIONS 3

1. Five generations

2. Very Large Scale Integrated Circuits

3. Fourth Generation


1. Explain various types of computers.

2. Explain in brief the various generations in computer technology.

3. Write a short note on Fifth Generation of computer. What makes it different from Fourth

Generation computer?

4. Why did the size of computer get reduced in Third Generation computer?

State True or False

1. (a) Word processor is Software Package that enables you to create, edit, print and save document .

(b) WordStar is a popular Word processor.

(c) Changing the size of the margins cannot reformat complete document or part of the text.

(d) Word has the facility of Macros.

(e) Word does not allow the user to mix the graphical pictures with text.

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1.Choose the best answer.

(a) While working in Ms-Word you have to work with

(i) Mouse only

(ii) Keyboard only

(iii) Both mouse and keyboard

(b) In Ms- Word every command is available in

(i) Print

(ii) Letter

(iii) Icons

(c) You can go inside Ms-Word by the following way

(i) Take the mouse pointer to START button on the task bar and click the left mouse

button.

(ii) Take the mouse pointer to START button and click the right mouse button.

(iii) Move the mouse pointer on the screen.

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LESSON 2

COMPUTER ORGANISATION

2.1 INTRODUCTION

In the previous lesson we discussed about the evolution of computer. In this lesson we will provide

you with an overview of the basic design of a computer. You will know how different parts of a

computer are organised and how various operations are performed between different parts to do a

specific task. As you know from the previous lesson the internal architecture of computer may differ

from system to system, but the basic organisation remains the same for all computer systems.

2.2 OBJECTIVES

At the end of the lesson you will be able to:

understand basic organisation of computer system

understand the meaning of Arithmetic Logical Unit, Control Unit and Central Processing Unit

differentiate between bit , byte and a word

define computer memory

differentiate between primary memory and secondary memory

differentiate between primary storage and secondary storage units

differentiate between input devices and output devices

2.3 BASIC COMPUTER OPERATIONS

A computer as shown in Fig. 2.1 performs basically five major operations or functions irrespective of

their size and make. These are 1) it accepts data or instructions by way of input, 2) it stores data, 3) it

can process data as required by the user, 4) it gives results in the form of output, and 5) it controls all

operations inside a computer. We discuss below each of these operations.

1. Input: This is the process of entering data and programs in to the computer system. You should

know that computer is an electronic machine like any other machine which takes as inputs raw data

and performs some processing giving out processed data. Therefore, the input unit takes data from us

to the computer in an organized manner for processing.

2. Storage: The process of saving data and instructions permanently is known as storage. Data has to

be fed into the system before the actual processing starts. It is because the processing speed of Central

Processing Unit (CPU) is so fast that the data has to be provided to CPU with the same speed.

Therefore the data is first stored in the storage unit for faster access and processing. This storage unit

or the primary storage of the computer system is designed to do the above functionality. It provides

space for storing data and instructions.

The storage unit performs the following major functions:

All data and instructions are stored here before and after processing.

Intermediate results of processing are also stored here.

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3. Processing: The task of performing operations like arithmetic and logical operations is called

processing. The Central Processing Unit (CPU) takes data and instructions from the storage unit and

makes all sorts of calculations based on the instructions given and the type of data provided. It is then

sent back to the storage unit.

4. Output: This is the process of producing results from the data for getting useful information.

Similarly the output produced by the computer after processing must also be kept somewhere inside

the computer before being given to you in human readable form. Again the output is also stored inside

the computer for further processing.

5. Control: The manner how instructions are executed and the above operations are performed.

Controlling of all operations like input, processing and output are performed by control unit. It takes

care of step by step processing of all operations in side the computer.

2.4 FUNCTIONAL UNITS

In order to carry out the operations mentioned in the previous section the computer allocates the task

between its various functional units. The computer system is divided into three separate units for its

operation. They are 1) arithmetic logical unit, 2) control unit, and 3) central processing unit.

2.4.1 Arithmetic Logical Unit (ALU)

After you enter data through the input device it is stored in the primary storage unit. The actual

processing of the data and instruction are performed by Arithmetic Logical Unit. The major

operations performed by the ALU are addition, subtraction, multiplication, division, logic and

comparison. Data is transferred to ALU from storage unit when required. After processing the output

is returned back to storage unit for further processing or getting stored.

2.4.2 Control Unit (CU)

The next component of computer is the Control Unit, which acts like the supervisor seeing that things

are done in proper fashion. The control unit determines the sequence in which computer programs and

instructions are executed. Things like processing of programs stored in the main memory,

interpretation of the instructions and issuing of signals for other units of the computer to execute

them. It also acts as a switch board operator when several users access the computer simultaneously.

Thereby it coordinates the activities of computer’s peripheral equipment as they perform the input and

output. Therefore it is the manager of all operations mentioned in the previous section..

2.4.3 Central Processing Unit (CPU)

The ALU and the CU of a computer system are jointly known as the central processing unit. You may

call CPU as the brain of any computer system. It is just like brain that takes all major decisions,

makes all sorts of calculations and directs different parts of the computer functions by activating and

controlling the operations.

Personal Computer Configuration

Now let us identify the physical components that make the computer work. These are

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1. Central Processing Unit (CPU)

2. Computer Memory (RAM and ROM)

3. Data bus

4. Ports

5. Motherboard

6. Hard disk

7. Output Devices

8. Input Devices

All these components are inter-connected for the personal computer to work.

IN-TEXT QUESTIONS 1

1. What are the five basic operations performed by the computer?

2. Define ALU, CU and CPU.

3. Choose the correct answer:

(a) The task of performing arithmetic and logical operations is called

(i) ALU (ii) editing (iii) storage (iv) output

(b) The ALU and CU jointly known as

(i) RAM (ii) ROM (iii) CPU (iv) none of the above

(c) The process of producing results from the data for getting useful information

(i) output (ii)input (iii) processing (iv) storage

2.5 MEMORY SYSTEM IN A COMPUTER

There are two kinds of computer memory: primary and secondary. Primary memory is accessible

directly by the processing unit. RAM is an example of primary memory. As soon as the computer is

switched off the contents of the primary memory is lost. You can store and retrieve data much faster

with primary memory compared to secondary memory. Secondary memory such as floppy disks,

magnetic disk, etc., is located outside the computer. Primary memory is more expensive than

secondary memory. Because of this the size of primary memory is less than that of secondary

memory. We will discuss about secondary memory later on.

Computer memory is used to store two things: i) instructions to execute a program and ii) data. When

the computer is doing any job, the data that have to be processed are stored in the primary memory.

This data may come from an input device like keyboard or from a secondary storage device like a

floppy disk.

As program or the set of instructions is kept in primary memory, the computer is able to follow in -

stantly the set of instructions. For example, when you book ticket from railway reservation counter,

the computer has to follow the same steps: take the request, check the availability of seats, calculate

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fare, wait for money to be paid, store the reservation and get the ticket printed out. The programme

containing these steps is kept in memory of the computer and is followed for each request.

But inside the computer, the steps followed are quite different from what we see on the monitor or

screen. In computer’s memory both programs and data are stored in the binary form. You have

already been introduced with decimal number system, that is the numbers 1 to 9 and 0. The binary

system has only two values 0 and 1. These are called bits. As human beings we all understand decimal

system but the computer can only understand binary system. It is because a large number of integrated

circuits inside the computer can be considered as switches, which can be made ON, or OFF. If a

switch is ON it is considered 1 and if it is OFF it is 0. A number of switches in different states will

give you a message like this: 110101....10. So the computer takes input in the form of 0 and 1 and

gives output in the form 0 and 1 only. Is it not absurd if the computer gives outputs as 0’s & 1’s only?

But you do not have to worry about. Every number in binary system can be converted to decimal

system and vice versa; for example, 1010 meaning decimal 10. Therefore it is the computer that takes

information or data in decimal form from you, convert it in to binary form, process it producing

output in binary form and again convert the output to decimal form.

The primary memory as you know in the computer is in the form of IC’s (Integrated Circuits). These

circuits are called Random Access Memory (RAM). Each of RAM’s locations stores one byte of

information. (One byte is equal to 8 bits). A bit is an acronym for binary digit, which stands for one

binary piece of information. This can be either 0 or 1. You will know more about RAM later. The

Primary or internal storage section is made up of several small storage locations (ICs) called cells.

Each of these cells can store a fixed number of bits called word length.

Each cell has a unique number assigned to it called the address of the cell and it is used to identify the

cells. The address starts at 0 and goes up to (N-1). You should know that the memory is like a large

cabinet containing as many drawers as there are addresses on memory. Each drawer contains a word

and the address is written on outside of the drawer.

Capacity of Primary Memory

You know that each cell of memory contains one character or 1 byte of data. So the capacity is

defined in terms of byte or words. Thus 64 kilobyte (KB) memory is capable of storing 64 1024 =

32,768 bytes. (1 kilobyte is 1024 bytes). A memory size ranges from few kilobytes in small systems

to several thousand kilobytes in large mainframe and super computer. In your personal computer you

will find memory capacity in the range of 64 KB, 4 MB, 8 MB and even 16 MB (MB = Million

bytes).

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The following terms related to memory of a computer are discussed below:

1. Random Access Memory (RAM): The primary storage is referred to as random access memory

(RAM) because it is possible to randomly select and use any location of the memory directly store

and retrieve data. It takes same time to any address of the memory as the first address. It is also

called read/write memory. The storage of data and instructions inside the primary storage is

temporary. It disappears from RAM as soon as the power to the computer is switched off. The

memories, which loose their content on failure of power supply, are known as volatile

memories .So now we can say that RAM is volatile memory.

2. Read Only Memory (ROM): There is another memory in computer, which is called Read Only

Memory (ROM). Again it is the ICs inside the PC that form the ROM. The storage of program

and data in the ROM is permanent. The ROM stores some standard processing programs supplied

by the manufacturers to operate the personal computer. The ROM can only be read by the CPU

but it cannot be changed. The basic input/output program is stored in the ROM that examines and

initializes various equipment attached to the PC when the switch is made ON. The memories,

which do not loose their content on failure of power supply, are known as non-volatile memories.

ROM is non-volatile memory.

3. PROM There is another type of primary memory in computer, which is called Programmable

Read Only Memory (PROM). You know that it is not possible to modify or erase programs stored

in ROM, but it is possible for you to store your program in PROM chip. Once the programmes are

written it cannot be changed and remain intact even if power is switched off. Therefore programs

or instructions written in PROM or ROM cannot be erased or changed.

4. EPROM: This stands for Erasable Programmable Read Only Memory, which over come the

problem of PROM & ROM. EPROM chip can be programmed time and again by erasing the

information stored earlier in it. Information stored in EPROM exposing the chip for some time

ultraviolet light and it erases chip is reprogrammed using a special programming facili ty. When

the EPROM is in use information can only be read.

5. Cache Memory: The speed of CPU is extremely high compared to the access time of main

memory. Therefore the performance of CPU decreases due to the slow speed of main memory. To

decrease the mismatch in operating speed, a small memory chip is attached between CPU and

Main memory whose access time is very close to the processing speed of CPU. It is called

CACHE memory. CACHE memories are accessed much faster than conventional RAM. It is used

to store programs or data currently being executed or temporary data frequently used by the CPU.

So each memory makes main memory to be faster and larger than it really is. It is also very

expensive to have bigger size of cache memory and its size is normally kept small.

6. Registers: The CPU processes data and instructions with high speed, there is also movement of

data between various units of computer. It is necessary to transfer the processed data with high

speed. So the computer uses a number of special memory units called registers. They are not part

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of the main memory but they store data or information temporarily and pass it on as directed by

the control unit.

IN-TEXT QUESTIONS 2

1. Distinguish between bit and byte.

2. Define volatile and non-volatile memory.

3. Write True or False:

(a) There are two kinds of computer memory primary and secondary.

(b) The computer takes inputs in the form of 0 and 1.

(c) The storage of program and data in the RAM is permanent.

(d) PROM is secondary memory.

(e) The memories which do not loose their content on failure of power supply are known as non-

volatile memories.

2.6 SECONDARY STORAGE

You are now clear that the operating speed of primary memory or main memory should be as

fast as possible to cope up with the CPU speed. These high-speed storage devices are very

expensive and hence the cost per bit of storage is also very high. Again the storage capacity of

the main memory is also very limited. Often it is necessary to store hundreds of millions of

bytes of data for the CPU to process. Therefore additional memory is required in all the

computer systems. This memory is called auxiliary memory or secondary storage.

In this type of memory the cost per bit of storage is low. However, the operating speed is

slower than that of the primary storage. Huge volume of data are stored here on permanent

basis and transferred to the primary storage as and when required. Most widely used

secondary storage devices are magnetic tapes and magnetic disk.

1. Magnetic Tape: Magnetic tapes are used for large computers like mainframe computers

where large volume of data is stored for a longer time. In PC also you can use tapes in the

form of cassettes. The cost of storing data in tapes is inexpensive. Tapes consist of magnetic

materials that store data permanently. It can be 12.5 mm to 25 mm wide plastic film-type and

500 meter to 1200 meter long which is coated with magnetic material. The deck is connected

to the central processor and information is fed into or read from the tape through the

processor. It similar to cassette tape recorder.

15

Advantages of Magnetic Tape:

Compact: A 10-inch diameter reel of tape is 2400 feet long and is able to

hold 800, 1600 or 6250 characters in each inch of its length. The maximum capacity

of such tape is 180 million characters. Thus data are stored much more compactly on

tape.

Economical: The cost of storing characters is very less as compared to other

storage devices.

Fast: Copying of data is easier and fast.

Long term Storage and Re-usability: Magnetic tapes can be used for long

term storage and a tape can be used repeatedly with out loss of data.

2. Magnetic Disk: You might have seen the gramophone record, which is circular like a disk

and coated with magnetic material. Magnetic disks used in computer are made on the same

principle. It rotates with very high speed inside the computer drive. Data is stored on both the

surface of the disk. Magnetic disks are most popular for direct access storage device. Each

disk consists of a number of invisible concentric circles called tracks. Information is recorded

on tracks of a disk surface in the form of tiny magnetic spots. The presence of a magnetic spot

represents one bit and its absence represents zero bit. The information stored in a disk can be

read many times without affecting the stored data. So the reading operation is non-destructive.

But if you want to write a new data, then the existing data is erased from the disk and new

data is recorded.

3. Floppy Disk: It is similar to magnetic disk discussed above. They are 5.25 inch or 3.5 inch in

diameter. They come in single or double density and recorded on one or both surface of the

diskette. The capacity of a 5.25-inch floppy is 1.2 mega bytes whereas for 3.5 inch floppy it is

1.44 mega bytes. It is cheaper than any other storage devices and is portable. The floppy is a

low cost device particularly suitable for personal computer system.

4. Optical Disk:

With every new application and software there is greater demand for memory capacity. It is

the necessity to store large volume of data that has led to the development of optical disk

storage medium. Optical disks can be divided into the following categories:

1. Compact Disk/ Read Only Memory (CD-ROM): CD-ROM disks are made of reflective

metals. CD-ROM is written during the process of manufacturing by high power laser

beam. Here the storage density is very high, storage cost is very low and access time is

relatively fast. Each disk is approximately 4 1/2 inches in diameter and can hold over 600

16

MB of data. As the CD-ROM can be read only we cannot write or make changes into the

data contained in it.

2. Write Once, Read Many (WORM): The inconvenience that we can not write any thing in

to a CD-ROM is avoided in WORM. A WORM allows the user to write data permanently

on to the disk. Once the data is written it can never be erased without physically

damaging the disk. Here data can be recorded from keyboard, video scanner, OCR

equipment and other devices. The advantage of WORM is that it can store vast amount of

data amounting to gigabytes (109 bytes). Any document in a WORM can be accessed very

fast, say less than 30 seconds.

3. Erasable Optical Disk: These are optical disks where data can be written, erased and re-

written. This also applies a laser beam to write and re-write the data. These disks may be

used as alternatives to traditional disks. Erasable optical disks are based on a technology

known as magnetic optical (MO). To write a data bit on to the erasable optical disk the

MO drive's laser beam heats a tiny, precisely defined point on the disk's surface and

magnetises it.

2.7 INPUT OUTPUT DEVICES

A computer is only useful when it is able to communicate with the external environment.

When you work with the computer you feed your data and instructions through some devices

to the computer. These devices are called Input devices. Similarly computer after processing,

gives output through other devices called output devices.

For a particular application one form of device is more desirable compared to others. We will

discuss various types of I/O devices that are used for different types of applications. They are

also known as peripheral devices because they surround the CPU and make a communication

between computer and the outer world.

2.7.1 Input Devices

Input devices are necessary to convert our information or data in to a form which can be understood

by the computer. A good input device should provide timely, accurate and useful data to the main

memory of the computer for processing followings are the most useful input devices.

1. Keyboard: - This is the standard input device attached to all computers. The layout of keyboard

is just like the traditional typewriter of the type QWERTY. It also contains some extra command

keys and function keys. It contains a total of 101 to 104 keys. A typical keyboard used in a

computer is shown in Fig. 2.6. You have to press correct combination of keys to input data. The

computer can recognise the electrical signals corresponding to the correct key combination and

processing is done accordingly.

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2. Mouse: - Mouse is an input device shown in Fig. 2.7 that is used with your personal computer. It

rolls on a small ball and has two or three buttons on the top. When you roll the mouse across a flat

surface the screen censors the mouse in the direction of mouse movement. The cursor moves very

fast with mouse giving you more freedom to work in any direction. It is easier and faster to move

through a mouse.

3. Scanner: The keyboard can input only text through keys provided in it. If we want to input a

picture the keyboard cannot do that. Scanner is an optical device that can input any graphical

matter and display it back. The common optical scanner devices are Magnetic Ink Character

Recognition (MICR), Optical Mark Reader (OMR) and Optical Character Reader (OCR).

Magnetic Ink Character Recognition (MICR): - This is widely used by banks to

process large volumes of cheques and drafts. Cheques are put inside the MICR. As they

enter the reading unit the cheques pass through the magnetic field which causes the read

head to recognise the character of the cheques.

Optical Mark Reader (OMR): This technique is used when students have appeared in

objective type tests and they had to mark their answer by darkening a square or circular

space by pencil. These answer sheets are directly fed to a computer for grading where

OMR is used.

Optical Character Recognition (OCR): - This technique unites the direct reading of any

printed character. Suppose you have a set of hand written characters on a piece of paper.

You put it inside the scanner of the computer. This pattern is compared with a site of

patterns stored inside the computer. Whichever pattern is matched is called a character

read. Patterns that cannot be identified are rejected. OCRs are expensive though better the

MICR.

2.7.2 Output Devices

1. Visual Display Unit: The most popular input/output device is the Visual Display Unit (VDU). It

is also called the monitor. A Keyboard is used to input data and Monitor is used to display the

input data and to receive massages from the computer. A monitor has its own box which is

separated from the main computer system and is connected to the computer by cable. In some

systems it is compact with the system unit. It can be color or monochrome.

2. Terminals: It is a very popular interactive input-output unit. It can be divided into two types:

hard copy terminals and soft copy terminals. A hard copy terminal provides a printout on paper

whereas soft copy terminals provide visual copy on monitor. A terminal when connected to a

CPU sends instructions directly to the computer. Terminals are also classified as dumb terminals

or intelligent terminals depending upon the work situation.

18

3. Printer: It is an important output device which can be used to get a printed copy of the processed

text or result on paper. There are different types of printers that are designed for different types of

applications. Depending on their speed and approach of printing, printers are classified as impact

and non-impact printers. Impact printers use the familiar typewriter approach of hammering a

typeface against the paper and inked ribbon. Dot-matrix printers are of this type. Non-impact

printers do not hit or impact a ribbon to print. They use electro-static chemicals and ink-jet

technologies. Laser printers and Ink-jet printers are of this type. This type of printers can produce

color printing and elaborate graphics.

Fig. 2.8

IN-TEXT QUESTIONS 3

1. Distinguish between impact and non-impact printers.

2. Define soft copy and hard copy terminals.

3. Write True or False:

(a) Secondary memory is called Auxiliary memory.

(b) The magnetic tapes and magnetic disk are primary memories.

(c) A CD-ROM is read only memory.

(d) Mouse is an output device.

(e) Printer is an important output device.


In this lesson we discussed five basic operations that a computer performs. These are input, storage,

processing, output and control. A computer accepts data as input, stores it, processes it as the user

requires and provides the output in a desired format. The storage unit of a computer is divided into

two parts: primary storage and secondary storage. We have discussed the devices used for these two

types of storage and their usefulness.


1. What are the five basic operations performed by any computer system?

2. Draw a block diagram to illustrate the basic organization of computer system and explain the

function of various units.

3. What is input device? How does it differ from output device?

4. Differentiate between RAM and ROM. Also distinguish between PROM and EPROM.

19

5. What is cache memory? How is it different from primary memory?

6. Write short notes on (a) Control Unit (b) Random Access Memory (RAM)


IN-TEXT QUESTIONS 1

1. The five basic operations that a computer performs are input, storage, processing, output and

control.

2. ALU: Arithmetic Logic Unit

CU: Control Unit

CPU: Central Processing Unit

3. (a) i (b) iii (c) i

IN-TEXT QUESTIONS 2

1. A bit is an acronym for binary digit, which stands for one binary piece of information. This

can be either 0 or 1. A byte is equal to 8 bits.

2. The memories which are erased if there is a power failure are known as volatile memories.

RAM is an example of volatile memory. The memories, which do not loose their content on

failure of power supply, are known as non-volatile memories. ROM is non-volatile memory.

3. (a) T (b) T (c) F (d) F (e) T

IN-TEXT QUESTIONS 3

1. Impact printers use the familiar typewriter approach of hammering a typeface against the

paper and inked ribbon. Non-impact printers do not hit or impact a ribbon to print. They use

electro-static chemicals and ink-jet technologies.

2. A hard copy terminal provides a printout on paper whereas soft copy terminals provide visual

copy on monitor.

3. (a) T (b) F (c) T (d) F (e) T

LESSON 3

LANGUAGE/SOFTWARE

3.1 INTRODUCTION

20

In the previous lesson we discussed about the different parts and configurations of computer. It has

been mentioned that programs or instructions have to be fed to the computer to do specific task. So it

is necessary to provide sequence of instructions so that your work can be done. We can divide the

computer components into two major areas, namely, hardware and software. Hardware is the

machine itself and its various individual equipment. It includes all mechanical, electronic and

magnetic devices such as monitor, printer, electronic circuit, floppy and hard disk. In this lesson we

will discuss about the other part, namely, software.

3.2 OBJECTIVES

After going through this lesson you will be able to

explain the concept of software

distinguish between different types of software

differentiate application software from system software

define a language

differentiate between different types of language

distinguish between compiler and interpreter

3.3 WHAT IS SOFTWARE?

As you know computer cannot do anything without instructions from the user. In order to do any

specific job you have to give a sequence of instructions to the computer. This set of instructions is

called a computer program. Software refers to the set of computer programs, procedures that describe

the programs, how they are to be used. We can say that it is the collection of programs, which

increase the capabilities of the hardware. Software guides the computer at every step where to start

and stop during a particular job. The process of software development is called programming.

You should keep in mind that software and hardware are complementary to each other. Both have to

work together to produce meaningful result. Another important point you should know that producing

software is difficult and expensive.

3.4 SOFTWARE TYPES

Computer software is normally classified into two broad categories.

Application Software

System software

21

Application Software: Application Software is a set of programs to carry out operations for a

specific application. For example, payroll is an application software for an organization to produce

pay slips as an output. Application software is useful for word processing, billing system, accounting,

producing statistical report, analysis of numerous data in research, weather forecasting, etc. In later

modules you will learn about MS WORD, Lotus 1-2-3 and dBASE III Plus. All these are application

softwares.

Another example of application software is programming language. Among the programming

languages COBOL (Common Business Oriented Language) is more suitable for business application

whereas FORTRAN (Formula Translation) is useful for scientific application. We will discuss about

languages in next section.

System Software: You know that an instruction is a set of programs that has to be fed to the

computer for operation of computer system as a whole. When you switch on the computer the

programs written in ROM is executed which activates different units of your computer and makes it

ready for you to work on it. This set of program can be called system software. Therefore system

software may be defined as a set of one or more programs designed to control the operation of

computer system.

System software are general programs designed for performing tasks such as controlling all operations

required to move data into and out of the computer. It communicates with printers, card reader, disk,

tapes etc. monitor the use of various hardware like memory, CPU etc. Also system software are

essential for the development of applications software. System Software allows application packages

to be run on the computer with less time and effort. Remember that it is not possible to run

application software without system software.

Development of system software is a complex task and it requires extensive knowledge of computer

technology. Due to its complexity it is not developed in house. Computer manufactures build and

supply this system software with the computer system. DOS, UNIX and WINDOWS are some of the

widely used system software. Out of these UNIX is a multi-user operating system whereas DOS and

WINDOWS are PC-based. We will discuss in detail about DOS and WINDOWS in the next module.

So without system software it is impossible to operate your computer. The following picture is shown

in Fig. 3.1 relation between hardware, software and you as a user of computer system.

IN-TEXT QUESTIONS 1

22

1. What are program, programming and software?

2. Differentiate between system software and application software.

3. Write True or False

(a) The set of instructions given to the computer is called programming.

(b) Application Software is a set of programs to carry out operations for a specific application.

(c) UNIX is a multi-user operating system.

3.5 WHAT IS LANGUAGE?

You are aware with the term language. It is a system of communication between you and me. Some of

the basic natural languages that we are familiar with are English, Hindi, Oriya etc. These are the

languages used to communicate among various categories of persons. But how you will communicate

with your computer. Your computer will not understand any of these natural languages for transfer of

data and instruction. So there are programming languages specially developed so that you could pass

your data and instructions to the computer to do specific job. You must have heard names like

FORTRAN, BASIC, COBOL etc. These are programming languages. So instructions or programs are

written in a particular language based on the type of job. As an example, for scientific application

FORTRAN and C languages are used. On the other hand COBOL is used for business applications.

3.5.1 Programming Languages

There are two major types of programming languages. These are Low Level Languages and High

Level Languages. Low Level languages are further divided in to Machine language and Assembly

language.

3.5.2 Low Level Languages

The term low level means closeness to the way in which the machine has been built. Low level

languages are machine oriented and require extensive knowledge of computer hardware and its

configuration.

(a) Machine Language

Machine Language is the only language that is directly understood by the computer. It does not needs

any translator program. We also call it machine code and it is written as strings of 1's (one) and 0’s

(zero). When this sequence of codes is fed to the computer, it recognizes the codes and converts it in

to electrical signals needed to run it. For example, a program instruction may look like this:

23

1011000111101

It is not an easy language for you to learn because of its difficult to understand. It is efficient for the

computer but very inefficient for programmers. It is considered to the first generation language. It is

also difficult to debug the program written in this language.

Advantage

The only advantage is that program of machine language run very fast because no translation

program is required for the CPU.

Disadvantages

1. It is very difficult to program in machine language. The programmer has to know details of

hardware to write program.

2. The programmer has to remember a lot of codes to write a program which results in program

errors.

3. It is difficult to debug the program.

(b) Assembly Language

It is the first step to improve the programming structure. You should know that computer can handle

numbers and letter. Therefore some combination of letters can be used to substitute for number of

machine codes.

The set of symbols and letters forms the Assembly Language and a translator program is required to

translate the Assembly Language to machine language. This translator program is called Àssembler'.

It is considered to be a second-generation language.

Advantages:

1. The symbolic programming of Assembly Language is easier to understand and saves a lot of time

and effort of the programmer.

2. It is easier to correct errors and modify program instructions.

3. Assembly Language has the same efficiency of execution as the machine level language. Because

this is one-to-one translator between assembly language program and its corresponding machine

language program.

Disadvantages:

1. One of the major disadvantages is that assembly language is machine dependent. A program

written for one computer might not run in other computers with different hardware configuration.

24

IN-TEXT QUESTIONS 2

1. What is the difference between FORTRAN and COBOL?

2. Differentiate between machine language and Assembly language.


(a) Low level language and High level language are two major types of programming

languages.

(b) Machine language is the only language that is indirectly understood by the computer.

(c) Assembly language is second generation language.

3.6 HIGH LEVEL LANGUAGES

You know that assembly language and machine level language require deep knowledge of computer

hardware where as in higher language you have to know only the instructions in English words and

logic of the problem irrespective of the type of computer you are using.

Higher level languages are simple languages that use English and mathematical symbols like +, -, %, /

etc. for its program construction.

You should know that any higher level language has to be converted to machine language for the

computer to understand.

Higher level languages are problem-oriented languages because the instructions are suitable for

solving a particular problem. For example COBOL (Common Business Oriented Language) is mostly

suitable for business oriented language where there is very little processing and huge output. There

are mathematical oriented languages like FORTRAN (Formula Translation) and BASIC (Beginners

All-purpose Symbolic Instruction Code) where very large processing is required.

Thus a problem oriented language designed in such a way that its instruction may be written more

like the language of the problem. For example, businessmen use business term and scientists use

scientific terms in their respective languages.

Advantages of High Level Languages

Higher level languages have a major advantage over machine and assembly languages that higher

level languages are easy to learn and use. It is because that they are similar to the languages used by

us in our day to day life.

3.6.1 Compiler

25

It is a program translator that translates the instruction of a higher level language to machine

language. It is called compiler because it compiles machine language instructions for every program

instructions of higher level language. Thus compiler is a program translator like assembler but more

sophisticated. It scans the entire program first and then translates it into machine code.

The programs written by the programmer in higher level language is called source program. After this

program is converted to machine languages by the compiler it is called object program.

Higher Level Language

---------------------------------- (Compile) Program Machine Language

Program

Fig. 3.2

A compiler can translate only those source programs, which have been written, in that language for

which the compiler is meant for. For example FORTRAN compiler will not compile source code

written in COBOL language.

Object program generated by compiler is machine dependent. It means programs compiled for one

type of machine will not run in another type. Therefore every type of machine must have its personal

compiler for a particular language. Machine independence is achieved by using one higher level

language in different machines.

3.6.2 Interpreter

An interpreter is another type of program translator used for translating higher level language into

machine language. It takes one statement of higher level languages, translate it into machine language

and immediately execute it. Translation and execution are carried out for each statement. It differs

from compiler, which translate the entire source program into machine code and does involve in its

execution.

.

The advantage of interpreter compared to compiler is its fast response to changes in source program.

It eliminates the need for a separate compilation after changes to each program. Interpreters are easy

to write and do not require large memory in computer. The disadvantage of interpreter is that it is time

consuming method because each time a statement in a program is executed then it is first translated.

Thus compiled machine language program runs much faster than an interpreted program.

26

IN-TEXT QUESTIONS 3

1. What is the difference between interpreter and compiler?

2. Give some examples of high level language.


(a) High level languages are problem-oriented language.

(b) Object program generated by compiler is machine independent.

(c) The disadvantage of interpreter is that it is time consuming.


In this lesson we discussed about two types of software, namely, system software and application

software. System software controls the hardware part of the computer. It is designed for performing

tasks such as controlling all operations required to move data into and out of the computer. It

communicates with printer, card reader, disk, tapes, etc. and monitors the use of various components

like memory, CPU, etc. DOS, UNIX and WINDOWS are three important system softwares.

Application software is a set of programs written for specific purpose. Examples of application

softwares are MS WORD, Lotus 1-2-3, COBOL, BASIC and FORTRAN. We have discussed about

levels of computer language.


1. What is software and hardware?

2. What is computer Language?

3. Name the three different categories of computer languages.

4. What is machine language? Why is it required?

5. What are advantages and disadvantages of machine language .

6 What is assembly language? What are its advantages over machine languages?

7 What is the difference between source program and object program?

8 What is higher level languages? Why are higher level languages are easier to use.

9 What is compiler? Why is it required?

10 What is interpreter? How does it differ from compiler?


IN-TEXT QUESTIONS 1

1. Program is a set of instructions given to the computer by the user. Software is a set of computer

programs and procedures that describe the programs. Programming is the process of software

development.

27

2. Application Software is a set of programs to carry out operations for a specific application.

System software is a set of programs written for performing tasks such as controlling all operations

required to move data into and out of the computer.

3. (a) False b) T rue (c) True

IN-TEXT QUESTIONS 2

1. FORTRAN is used for scientific applications whereas COBOL is used for business applications.

2. Machine Languages are the only language that is directly understood by the computer. It is

written in binary form that is 0 and 1. The set of symbols and letters forms the Assembly Language.

3. (a) True (b) False (c) True

IN-TEXT QUESTIONS 3

1. Both compiler and interpreter are program translators used for translating higher level language

into machine language. While compiler scans the entire program first and then translates it into

machine code, an Interpreter translates the program line by line.

2. FORTRAN (Formula Translation) and BASIC (Beginners All-purpose Symbolic Instruction

Code) are some of the high level languages.

3. (a) True (b) False (c) True

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LESSON 4

COMMUNICATION AND COMPUTER NETWORK

4.1 INTRODUCTION

Today computer is available in many offices and homes and therefore there is a need to share data and

programs among various computers with the advancement of data communication facilities. The

communication between computers has increased and it thus it has extended the power of computer

beyond the computer room. Now a user sitting at one place can communicate computers of any

remote sites through communication channel. The aim of this chapter is to introduce you the various

aspects of computer network.

4.2 OBJECTIVES

After going through this lesson you will be in a position to:

explain the concept of data communication

understand the use of computer network

identify different components of computer network

identify different types of network

explain communication protocols

understand what is internet and email and its uses in modern communication

appreciate the use of satellite communication.

4.3 DATA COMMUNICATION

We all are acquainted with some sorts of communication in our day to day life. For communication of

information and messages we use telephone and postal communication systems. Similarly data and

information from one computer system can be transmitted to other systems across geographical areas.

Thus data transmission is the movement of information using some standard methods. These methods

include electrical signals carried along a conductor, optical signals along an optical fibers and

electromagnetic areas.

Suppose a manager has to write several letters to various clients. First he has to use his PC and Word

Processing package to prepare his letter. If the PC is connected to all the client's PCs through

networking, he can send the letters to all the clients within minutes. Thus irrespective of geographical

areas, if PCs are connected through communication channel, the data and information, computer files

and any other program can be transmitted to other computer systems within seconds. The modern

form of communication like e-mail and Internet is possible only because of computer networking.

Basic Elements of a Communication System

The following are the basic requirements for working of a communication system.

1. A sender (source) which creates the message to be transmitted.

29

2. A medium that carries the message.

3. A receiver (sink) which receives the message.

In data communication four basic terms are frequently used. They are

Data: A collection of facts in raw forms that become information after processing.

Signals: Electric or electromagnetic encoding of data.

Signaling: Propagation of signals across a communication medium.

Transmission: Communication of data achieved by the processing of signals.

4.3.1 Communication Protocols

You may be wondering how do the computers send and receive data across communication links. The

answer is data communication software. It is this software that enables us to communicate with other

systems. The data communication software instructs computer systems and devices as to how exactly

data is to be transferred from one place to another. The procedure of data transformation in the form

of software is commonly called protocol.

The data transmission software or protocols perform the following functions for the efficient and error

free transmission of data.

Data sequencing: A long message to be transmitted is broken into smaller packets of fixed size for

error free data transmission.

Data Routing: It is the process of finding the most efficient route between source and destination

before sending the data.

Flow control: All machines are not equally efficient in terms of speed. Hence the flow control

regulates the process of sending data between fast sender and slow receiver.

Error Control: Error detecting and recovering is the one of the main function of communication

software. It ensures that data are transmitted without any error.

4.3.2 Data Transmission Modes

There are three ways for transmitting data from one point to another

1. Simplex: In simplex mode the communication can take place in one direction. The receiver

receives the signal from the transmitting device. In this mode the flow of information is Uni.-

directional. Hence it is rarely used for data communication.

2. Half-duplex: In half-duplex mode the communication channel is used in both directions, but only

in one direction at a time. Thus a half-duplex line can alternately send and receive data.

3. Full-duplex: In full duplex the communication channel is used in both directions at the same

time. Use of full-duplex line improves the efficiency as the line turn-around time required in half-

duplex arrangement is eliminated. Example of this mode of transmission is the telephone line.

30

A B

Simplex A to B only

A B

Half-Duplex A to B or B to A

A B

Full-Duplex A to B and B to A

Fig. 4.1

4.3.3 Digital and Analog Transmission

Data is transmitted from one point to another point by means of electrical signals that may be in

digital and analog form. So one should know the fundamental difference between analog and digital

signals. In analog signal the transmission power varies over a continuous range with respect to sound,

light and radio waves. On the other hand a digital signal may assume only discrete set of values within

a given range. Examples are computer and computer related equipment. Analog signal is measured in

Volts and its frequency in Hertz (Hz). A digital signal is a sequence of voltage represented in binary

form. When digital data are to be sent over an analog form the digital signal must be converted to

analog form. So the technique by which a digital signal is converted to analog form is known as

modulation. And the reverse process, that is the conversion of analog signal to its digital form, is

known as demodulation. The device, which converts digital signal into analog, and the reverse, is

known as modem.

Time

Analog Signal

Digital Signal

Fig. 4.2

4.3.4 Asynchronous and Synchronous Transmission

Data transmission through a medium can be either asynchronous or synchronous. In asynchronous

31

transmission data is transmitted character by character as you go on typing on a keyboard. Hence

there is irregular gaps between characters. However, it is cheaper to implement, as you do not have to

save the data before sending. On the other hand, in the synchronous mode, the saved data is

transmitted block by block. Each block can contain many characters. Synchronous transmission is

well suited for remote communication between a computer and related devices like card reader and

printers.

Following are the major communication devices used to day.

Wire Pairs: Wire pairs are commonly used in local telephone communication and for short distance

digital data communication. They are usually made up of copper and the pair of wires is twisted

together. Data transmission speed is normally 9600 bits per second in a distance of 100 meter.

Coaxial Cables: Coaxial cable is groups of specially wrapped and insulted wires that are able to

transfer data at higher rate. They consist of a central copper wire surrounded by an insulation over

which copper mesh is placed. They are used for long distance telephone lines and local area

network for their noise immunity and faster data transfer.

Microwave: Microwave system uses very high frequency radio signals to transmit data through

space. The transmitter and receiver of a microwave system should be in line-of-sight because the

radio signal cannot bend. With microwave very long distance transmission is not possible. In

order to overcome the problem of line of sight and power amplification of weak signal, repeaters

are used at intervals of 25 to 30 kilometers between the transmitting and receiving end.

Communication Satellite: The problem of line-sight and repeaters are overcome by using satellites

which are the most widely used data transmission media in modern days. A communication

satellite is a microwave relay station placed in outer space. INSAT-1B is such a satellite that can

be accessible from anywhere in India. In satellite communication, microwave signal is transmitted

from a transmitter on earth to the satellite at space. The satellite amplifies the weak signal and

transmits it back to the receiver. The main advantage of satellite communication is that it is a

single microwave relay station visible from any point of a very large area. In microwave the data

transmission rate is 16 giga bits per second. They are mostly used to link big metropolitan cities.

IN-TEXT QUESTIONS 1

1. What is communication protocol?

2. What is the difference between asynchronous and synchronous transmission?

3. State whether True or False

(a) The basic requirements for working of a communication system are sender medium and

32

receiver.

(b) Electric or Electromagnetic encoding of data is called Transmission.

(c) In full duplex the communication channel is used in both directions at the same time.

(d) Analog signal is measured in Volts and its frequency in Hertz

(e) The technique by which a digital signal is converted to analog form is known as

modulation.

4.4 COMPUTER NETWORK

A computer network is an interconnection of various computer systems located at different places. In

computer network two or more computers are linked together with a medium and data communication

devices for the purpose of communicating data and sharing resources. The computer that provides

resources to other computers on a network is known as server. In the network the individual

computers, which access shared network resources, are known as workstations or nodes.

Computer Networks may be classified on the basis of geographical area in two broad categories.

1. Local Area Network (LAN)

2. Wide Area Network (WAN)

4.4.1 Local Area Network

Networks used to interconnect computers in a single room, rooms within a building or buildings on

one site are called Local Area Network (LAN). LAN transmits data with a speed of several megabits

per second (106 bits per second). The transmission medium is normally coaxial cables.

LAN links computers, i.e., software and hardware, in the same area for the purpose of sharing

information. Usually LAN links computers within a limited geographical area because they must be

connected by a cable, which is quite expensive. People working in LAN get more capabilities in data

processing, work processing and other information exchange compared to stand-alone computers.

Because of this information exchange most of the business and government organisations are using

LAN.

Major Characteristics of LAN

every computer has the potential to communicate with any other computers of the network

high degree of interconnection between computers

easy physical connection of computers in a network

inexpensive medium of data transmission

high data transmission rate

Advantages

The reliability of network is high because the failure of one computer in the network does not

effect the functioning for other computers.

33

Addition of new computer to network is easy.

High rate of data transmission is possible.

Peripheral devices like magnetic disk and printer can be shared by other computers.

Disadvantages

If the communication line fails, the entire network system breaks down.

Use of LAN

Followings are the major areas where LAN is normally used

File transfers and Access

Word and text processing

Electronic message handling

Remote database access

Personal computing

Digital voice transmission and storage

4.4.2 Wide Area Network

The term Wide Area Network (WAN) is used to describe a computer network spanning a regional,

national or global area. For example, for a large company the head quarters might be at Delhi and

regional branches at Bombay, Madras, Bangalore and Calcutta. Here regional centers are connected to

head quarters through WAN. The distance between computers connected to WAN is larger. Therefore

the transmission medium used are normally telephone lines, microwaves and satellite links.

4.4.3 Characteristics of WAN

Followings are the major characteristics of WAN.

1. Communication Facility: For a big company spanning over different parts of the country the

employees can save long distance phone calls and it overcomes the time lag in overseas

communications. Computer conferencing is another use of WAN where users communicate with

each other through their computer system.

2. Remote Data Entry: Remote data entry is possible in WAN. It means sitting at any location you

can enter data, update data and query other information of any computer attached to the WAN but

located in other cities. For example, suppose you are sitting at Madras and want to see some data

of a computer located at Delhi, you can do it through WAN.

3. Centralised Information: In modern computerised environment you will find that big

organisations go for centralised data storage. This means if the organisation is spread over many

cities, they keep their important business data in a single place. As the data are generated at

different sites, WAN permits collection of this data from different sites and save at a single site.

4.4.4 Examples of WAN

1. Ethernet: Ethernet developed by Xerox Corporation is a famous example of WAN. This network

34

uses coaxial cables for data transmission. Special integrated circuit chips called controllers are

used to connect equipment to the cable.

2. Aparnet: The Aparnet is another example of WAN. It was developed at Advanced Research

Projects Agency of U. S. Department. This Network connects more than 40 universities and

institutions throughout USA and Europe.

Difference between LAN and WAN

LAN is restricted to limited geographical area of few kilometers. But WAN covers great distance

and operate nationwide or even worldwide.

In LAN, the computer terminals and peripheral devices are connected with wires and coaxial

cables. In WAN there is no physical connection. Communication is done through telephone lines

and satellite links.

Cost of data transmission in LAN is less because the transmission medium is owned by a single

organisation. In case of WAN the cost of data transmission is very high because the transmission

medium used are hired, either telephone lines or satellite links.

The speed of data transmission is much higher in LAN than in WAN. The transmission speed in

LAN varies from 0.1 to 100 megabits per second. In case of WAN the speed ranges from 1800 to

9600 bits per second (bps).

Few data transmission errors occur in LAN compared to WAN. It is because in LAN the distance

covered is negligible.

4.5 NETWORK TOPOLOGY

The term topology in the context of communication network refers to the way the computers or

workstations in the network are linked together. According to the physical arrangements of

workstations and nature of work, there are three major types of network topology. They are star

topology, bus topology and ring topology.

4.5.1 Star topology

In star topology a number of workstations (or nodes) are directly linked to a central node (see, Fig.

4.3). Any communication between stations on a star LAN must pass through the central node. There is

bi-directional communication between various nodes. The central node controls all the activities of

the nodes. The advantages of the star topology are:

35

It offers flexibility of adding or deleting of workstations from the network.

Breakdown of one station does not affect any other device on the network.

The major disadvantage of star topology is that failure of the central node disables communication

throughout the whole network.

Fig. 4.3: Star Topology

4.5.2 Bus Topology

In bus topology all workstations are connected to a single communication line called bus. In this type

of network topology there is no central node as in star topology. Transmission from any station travels

the length of the bus in both directions and can be received by all workstations. The advantage of the

bus topology is that

It is quite easy to set up.

If one station of the topology fails it does not affect the entire system.

The disadvantage of bus topology is that any break in the bus is difficult to identify.

Fig. 4.4: Bus Topology

4.5.3 Ring Topology

In ring topology each station is attached nearby stations on a point to point basis so that the entire

system is in the form of a ring. In this topology data is transmitted in one direction only. Thus the data

36

NODE CENTRAL NODE

bus

nodes

packets circulate along the ring in either clockwise or anti-clockwise direction. The advantage of this

topology is that any signal transmitted on the network passes through all the LAN stations. The

disadvantage of ring network is that the breakdown of any one station on the ring can disable the

entire system.

Fig. 4.5: Ring Topology

IN-TEXT QUESTIONS 2

1. Differentiate between LAN and WAN.

2. What are the different types of network topology?

3. State True or False

(a) Networks used to interconnect computers in a single room, rooms within a building or buildings

on one site are called Wide Area Network (WAN).

(b) The term Wide Area Network (WAN) is used to describe a computer network spanning a regional,

national or global area.

(c) The speed of data transmission is much higher in WAN than in LAN.

(d) In star topology a number of workstations (or nodes) are directly linked to a central node.

(e) The advantage of the bus topology is that, If one station of the topology fails it does not affect the

entire system.

4.6 INTERNET

The Internet is a network of networks. Millions of computers all over the world are connected through

the Internet. Computer users on the Internet can contact one another anywhere in the world. If your

computer is connected to the Internet, you can connect to millions of computers. You can gather

information and distribute your data. It is very much similar to the telephone connection where you

can talk with any person anywhere in the world.

In Internet a huge resource of information is accessible to people across the world. Information in

every field starting from education, science, health, medicine, history, and geography to business,

37

NODES

news, etc. can be retrieved through Internet. You can also download programs and software packages

from anywhere in the world. Due to the tremendous information resources the Internet can provide, it

is now indispensable to every organisation.

Origin of Internet

In 1969 Department of Defence (DOD) of USA started a network called ARPANET (Advanced

Research Projects Administration Network) with one computer at California and three at Utah. Later

on other universities and R & D institutions were allowed to connect to the Network. APARNET

quickly grew to encompass the entire American continent and became a huge success. Every

university in the country wanted to become a part of ARPANET. So the network was broken into two

smaller parts MILNET for managing military sites and ARPANET (smaller) for managing non-

military sites. Around 1980, NSFNET (National Science Foundation Network) was created. With the

advancement of modern communication facilities, other computers were also allowed to be linked up

with any computer of NSFNET. By 1990 many computers were looking up to NSFNET giving birth

to Internet.

How Internet functions

Internet is not a governmental organisation. The ultimate authority of the Internet is the Internet

Society. This is a voluntary membership organisation whose purpose is to promote global information

exchange. Internet has more than one million computers attached to it.

E-mail

E-mail stands for electronic mail. This is one of the most widely used features of Internet. Mails are

regularly used today where with the help of postage stamp we can transfer mails anywhere in the

world. With electronic mail the service is similar. But here data are transmitted through Internet and

therefore within minutes the message reaches the destination may it be anywhere in the world.

Therefore the mailing system is excessively fast and is being used widely for mail transfer.

IN-TEXT QUESTIONS 3

1. What is Internet?

2. What is e-mail?

3. How does Internet function?


In this lesson we discussed the importance and modes of communication through computers.

Computers can communicate with one another through computer networking. There are two types of

computer network: LAN and WAN. We discussed about the physical arrangements of computer and

38

peripherals in network topology. There are three types of network topology: star topology, bus

topology and ring topology. Also we discussed about Internet and e-mail.


1. What is computer Network? What are its main objectives?

2. Differentiate between analog and digital transmission of data.

3. Explain in brief different communication media.

4. What is the difference between simplex and full-duplex transmission?


IN-TEXT QUESTIONS 1

1. The data communication software instructs computer systems and devices as to how exactly data

is to be transferred from one place to another. The procedure of data transformation in the form of

software is commonly called protocol.

2. In asynchronous transmission data is transmitted character by character as you go on typing on a

keyboard. On the other hand, in the synchronous mode, the saved data is transmitted block by

block.

3. (a) True (b) False (c) True (d) True (e) True

IN-TEXT QUESTIONS 2

1. LAN is restricted to limited geographical area whereas WAN covers great distance. In LAN the

computer terminals and peripheral devices are connected with wires and coaxial cables whereas in

WAN communication is done through telephone lines and satellite links. The speed of data

transmission is much higher in LAN than in WAN.

2. There are three major types of network topology. They are star topology, bus topology and ring

topology.

3. (a) False (b) True (c) False (d) True (e) True

IN-TEXT QUESTIONS 3

1. The Internet is a network of networks. Information in every field starting from education, science,

health, medicine, history, and geography to business, news, etc. can be retrieved through Internet.

2. E-mail stands for electronic mail. Through e-mail we can transfer data anywhere in the world

within seconds.

3. Internet is not a governmental organisation. The ultimate authority of the Internet is the Internet

Society. This is a voluntary membership organisation whose purpose is to promote global

information exchange.

39

40

LESSON 24

ELEMENTS OF BASIC STRUCTURE

24.1 INTRODUCTION

In this lesson, you will be introduced to a programming language called BASIC. It is the most popular

conversational programming language. Various versions of BASIC have been developed by computer

manufacturers for their computers. This language is quite simple to understand and has been adopted

by most of the microcomputers. It is suitable for both mathematical and business problems. It has

been specially designed for use in `time-sharing' environment but can also be used as a standard

language in a `batch-processing' environment.

24.2 OBJECTIVES

At the end of this lesson, you should be able to

know how to construct constants, variables in BASIC language and expression using

mathematical, relational and logical operators.

learn the structure and essential elements of BASIC.

use some elementary BASIC commands in small programs.

24.3 BASIC AS A PROGRAMMING LANGUAGE

Basic is quite simple language and easy to understand. It is becoming more popular as an interactive

language. Now we shall discuss various features of this language.

24.3.1 Why BASIC?

B in BASIC stands for Beginners. Obviously, it is meant for those who are about to start learning

programming. To qualify as a beginner's language, it has to be simple, easy and readily available.

BASIC has all the qualities. Although, it is the beginner's language, its use by no means is restricted

to basic computer education or elementary applications. The second alphabet A stands for all-purpose.

It means BASIC can be used for a variety of applications involving business, science, mathematics

and graphics. In fact, with new enhancements, BASIC has some of the powers of more advanced

languages. The all purposeness is also derived from the fact that very large segments of games and

computer courseware are written in BASIC. The other three letters i.e. SIC stand for Symbolic

Instruction Code -- means the instructions may not be exactly in English but expressed in symbols.

The advantages of BASIC can be summed up as follows:

BASIC is easy to learn and fun to practice. It may be called a `People's language'.

It is available almost in every computer from micro to mainframe. Therefore, a program

developed in a micro can run on bigger system with minor modifications.

Program development cycle is quick, debugging is simple, and

41

Modification of programs is quite easy.

24.3.2 History of BASIC

Conceived by John Kemeny and Thomas Kurtz, BASIC was born at Dartmouth College, USA in

1964. It had a rather humble beginning. The classical languages like COBOL or FORTRAN were

already developed. COBOL, in fact, was already established as the major data processing language.

FORTRAN on the other hand, became the principal programming language for scientific applications.

Both these languages, however, were not very simple to learn. There were extensive rules on syntax

and structure of the programs. Because of its simplicity, BASIC gained immediate popularity. It

became a widely used language for small commercial and scientific applications. BASIC had the

same impact on the world of programming languages as the PC had on the larger computer systems.

BASIC's popularity and acceptance by the user community compelled all the major computer

manufacturers to come out with their individual version of BASIC. When the microcomputer or PCs

were introduced, BASIC found a most convenient vehicle for its proliferation. The ease and simplicity

of BASIC made it the standard programming language for the microcomputer world. Even your MS-

DOS operating system comes with a BASIC interpreter called BASICA. (MS-DOS 3.2 onwards, a

more enhanced BASIC version, i.e., GWBASIC forms the part of the operating system.) American

National Standards Institute (ANSI) in 1978 came out with a standardised version of BASIC

language. Most of the versions of the currently available BASIC include the features of the ANSI

standard.

24.4 STRUCTURE OF BASIC

The general structure of standard BASIC language is best understood by a practical program. The

following small program prints the words WELCOME TO NATIONAL OPEN SCHOOL on the

screen:

10 REM: This is my first program

20 PRINT "WELCOME TO NATIONAL OPEN SCHOOL"

30 END

Keeping this program in view, let us go over the rules on the structure of the language.

These are:

Each statement of instruction must appear on a separate line.

A statement cannot exceed 80 characters i.e. one line on the terminal.

A statement must start with a statement number. It is a positive integer.

No two statements can have the same numbers.

The statement must be in the ascending order.

Each statement number is followed by a BASIC command or keyword.

You may use blank space to increase the readability of the program.

42

There is no restriction on blank lines within a program. These are the rules, as applicable to standard

or "Dartmouth BASIC" as it is called. The Microsoft BASIC i.e. BASICA or GWBASIC, however,

has provision for more than one statement in the same line and the use of keywords also need not

follow a line number. But if you strictly follow the rules of standard BASIC, the program will still

remain valid in Microsoft or any other BASIC. Now let us learn about some of the keywords, you

came across in the program.

24.5 ELEMENTARY BASIC STATEMENTS

In the program, you came across their important BASIC commands or keywords. These are REM,

PRINT and END. We will briefly discuss REM and END here. The PRINT will be discussed in

greater details in subsequent lessons. Presently for the purpose of understanding, you may take

PRINT, as an output instruction. The output may be meant for the terminal (as in this case) or it may

be directed to a disk file. What is important, is to remember, that in BASIC, print does not necessarily

mean a print out on a paper; it may mean display on the terminal or write on a disk file also.

24.5.1 REM

The REM is the short form for REMARKS. At the time of execution, when the interpreter comes

across the first three alphabets, as the keyword, it knows that the content of the line following REM is

not meant for execution and is to be ignored. REM is used purely to enhance the documentation

aspect of a program. It is meant for the reader of the program to understand the contents, purpose,

logic and other such aspects. Whatever, information on the program, you want to convey to the reader

of the program, may be placed after REM. There is no limit on the number of REM statements in a

program. In fact, it is recommended that you get used to judicious and copious use of REM

statements. It may not only help the reader, but it may also help you in understanding your own

programs, particularly if those are old or lengthy. At times to enhance the presence of a REM

statement you may place a blank line above or below a statement. This makes it more visible in

lengthy programs. You can place a blank line by a PRINT statement. If we want to insert a blank line

after the REM statement of the program, we may write the program as:

10 REM : This is my first program

20 PRINT

30 PRINT "WELCOME TO NATIONAL OPEN SCHOOL"

40 END

24.5.2 END

43

The END statement was mandatory in the older BASIC version to indicate the end of a program. In

other BASIC like Microsoft BASIC, it is not compulsory. In such cases, the program terminates at the

last or highest line number. Whenever END is used, it must be the last line. Any statement after the

END is irrelevant to the interpreter. Having been familiarised with a small BASIC program, let us

now see the elements other than the keywords, comprising this language.

24.6 THE CHARACTER SET

BASIC has the character set consisting of the following elements:

(a) Alphabets: A, B, C, ----. Z

(b) Digits: 0,1,2, ----, 9 and

(c) Special characters: + - * / ( ) . , $ ; : = > < " ^

The symbol ^ (caret) is used to denote exponentiation operator, the symbol * (asterisk) is used to

denote multiplication and the other symbols have their usual meanings. In addition these, blank space

denoted by the symbol b is also regarded as a character.

24.7 CONSTANTS AND VARIABLES

A quantity in a computer program which does not change its value during the execution of the

program is called a constant and the quantity which may change its values during the execution of the

program is called a variable. BASIC allows the following constants:

Numeric constant

String constant

Numeric constant is one that is formed by a sequence of digits 0,1,2, ---, 9 and may include a decimal

point. A numeric constant known as number may be as integer or a real number. 383, + 57, 0, - 6.2

and 6.15E4 are valid numeric constants. The number 6.15E4, in fact, represent 6.15 104. The

notation E is used to represent exponential form. The number after E is the exponent which can be

positive or negative. However, its length cannot exceed two digits.

It is also important to keep in mind that

BASIC does not distinguish between an integer and a fraction.

Commands are not allowed in a numeric constant

The limit on the number of digits that can be used varies from computer to computer. Normally, a

numeric constant can have up to a maximum of eight digits.

44

A string constant consists of a sequence of characters. It must be enclosed by a quotation mark. This

may contain blank space as a character but it should not include the quotation mark. String constants

are used to represent non-numeric quantities such as names, addresses, etc. For example, "PANKAJ

GOEL", "SUM = Rs 75", "162" are a few valid string constants.

In BASIC, variables are also of two types. They are

Numeric variable

String variable

Numeric variable can assume numeric value and is represented by an alphabet or an alphabet followed

by another alphabet or a digit. For example A, C, A2, ABC, A6 etc, represent numeric variables. A

string variable is represented by an alphabet followed by dollar ($) sign. It should be kept in mind that

while constructing the string variable, dollar ($) should be the last character. For example, A1$,

PKG$, BOOK1$, etc., are valid string variables.

IN-TEXT QUESTION 1

1. The following numbers (constants) are not written correctly. Indicate the errors:

(a) 4,75,163,

(b) +-7567

(c) 3.64E 1.5

(d) 6.05E

(e) 6125 -

2. Which of the following BASIC strings are correct?

(a) January 26, 1997

(b) Sixty-two

(c) 5121942

(d) 100 - 40 =60

(e) SUM "10"

3. Write the following as ordinary numbers:

(a) 1.23E6

(b) 1.5E - 5

(c) - 3E + 2

(d) 5.865696 E + 6

45

(e) - 1.2 E -2

24.8 ARITHMETIC EXPRESSIONS

A BASIC system can handle arithmetic expressions involving the five arithmetic operators +

(addition), - (subtraction), *(multiplication), /(division) and ^ (exponentiation). The hierarchy of

operations is as follows:

(i) Exponentiation

(ii) Multiplication and division

(iii) Addition and subtraction

Thus, in a particular arithmetic expression, the order of execution is as per this hierarchy, i.e. all

exponentiation operations are performed first, then multiplication/division and the

addition/subtraction operations are the last to be carried out. Note that within a particular hierarchical

group, the operations are executed form left to right. Normal hierarchy of operations can be altered by

use of parentheses. The operations within the innermost parentheses are performed first and then the

second innermost and so on.

In addition to this hierarchy of operations, the following rules must be kept in mind in arithmetic

expression:

Two operations must not appear together. For example, C+-D, A/-C, etc are not permitted.

String constants and string variables should not be used in arithmetic expressions. For example,

P+P$ is wrong.

When brackets are used, they must be used in pairs, i.e., every left bracket must be matched with

a right bracket.

Denominator of an expression should not be zero.

Within a given pair of parentheses, the natural hierarchy of operations will apply.

Let us take an example where we give BASIC equivalents of a few algebraic expressions

Algebraic Expression BASIC Equivalent

2A+B 2*A+B

A(B+C) A*(B+C)

B2-4AC B^2-4*A*C

46

24.9 RELATIONAL OR LOGICAL EXPRESSIONS

A relational expression is formed by using any of the following relational operators:

Relational Operator Meaning

= Equal to

> Greater than

< Less than

< = Less than or equal to

> = Greater than or equal to

< > Not equal to

In the execution of programs, it is sometimes desired to compare two numerical quantities (or

sometimes string quantities) and take decisions on achieving certain conditions. For example, we may

be interested to check the number of repetitive calculations performed or to find out whether the

denominator of an arithmetic expression has become zero or if a particular quantity is negative, and so

on. Expressions written to compare two quantities using certain relational operators are known as

relational expressions. These expressions take only one of the two values, namely, TRUE or FALSE,

For instance, the relational expression A > B will be true if A is greater than B, otherwise FALSE.

This test result is used to change the sequence of execution of statements in a program. The general

form of a relational expression is as follows:

Relational

operator

When expressions are used on either side of the relational operators, the expressions will be evaluated

first and then the results of expressions compared. This means that relational operators come last in

the hierarchy of operators.

Logical expressions are used in IF---THEN Statements to determine the course of action of a running

program.

24.10 LOGICAL OPERATORS

Like relational operators, BASIC, also supports logical operators to perform logical operation on

numerical values. Logical operators are used to connect two or more relations and return a TRUE or

FALSE value to be used in a decision.

47

Constantor

Variableor

Expression

Constantor

Variableor

Expression

The common logical operators are:

AND Conjunction

OR Disjunction

NOT Logical Negation

For example, the expression A > 50 AND B > 150 is TRUE when A is more than 50 and at the same

time B is more than 150.

Logical operators return results as indicated in the following tables. T indicates a TRUE and F

indicates a FALSE. X and Y are relational expressions.

AND Operator

X Y X AND Y

T

T

F

F

T

F

T

F

T

F

F

F

OR Operator

X Y X OR Y

T

T

F

F

T

F

T

F

T

T

T

F

NOT Operator

X NOT X

T

F

F

T

24.11 LIBRARY FUNCTIONS IN BASIC

The word `library' stands for collection. In the context of computer languages, a library is essentially a

collection of useful programs. These programs are used by the programmers to simplify their task of

program development. These programs are often referred as subroutines. The programmer does not

have to know the details of the sub-routine. Most of the programming languages are offered with a

48

number of sub-routines called sub-routine library or library functions. These built-in library functions

are used to simplify some useful common functions like calculation of square root, log of a number or

cosine of an angle. BASIC's library is rich with mathematical functions. For example, suppose you

want to calculate the square root of a numeric variable A. In simple mathematics, square root of A,

i.e., can be written as A½. Thus in BASIC it can be written as:

10 LET B = A^0.5

The value of B will be the square root of A. Using a library function the operation can be performed

as

10 LET B = SQR(A)

Of course, from the example, it appears that there is hardly any benefit in using the library function.

But imagine, if problem is little more complicated like calculation of the sine value of an angle or

logarithm of a number. The programming algorithm to calculate these is not so simple. To find the

logarithm of by using LOG function you write

10 LET Y = LOG (X),

The variable Y will store the LOG value of X.

From this example, we may deduce the rules, governing the use of a function.

(a) Each function is assessed by the function name (LOG, SQR, etc.) followed by the function

argument placed within the parenthesis.

(b) The function argument is the information you supply to the function to act upon it. For

mathematical factions, it has to be a numeric constant or variable. Listed below are some

examples of mathematical functions in BASIC.

Function Name Purpose Example

SIN Sine Calculate the Sine SIN(X)

value of an SIN(44/7)

angle (in radians)

LOG LOG Calculate the natural LOG(X)

logarithm of a number LOG(100)

49

SQR Square root Calculate the square SQR(A)

root of a number SQR(100)

(c) The function name is to be written exactly as given. No deviation is permitted.

(d) You cannot have a blank space between function name (SIN, LOG etc.) and the beginning of the

opening parenthesis enclosing the argument.

It should be noted that a library function program would produce the result faster than a BASIC

program that has been written to perform the same task. For example, calculation of square root by the

SQR function will be faster than writing in the form of a program. This is due to the fact that library

functions are optimised for the particular BASIC interpreter provided by the supplier.

IN-TEXT QUESTION 2

1. Evaluate the following BASIC expressions:

(a) 3 * 4/2 ^ 3 + 1

(b) 2 * (3+4) / (5-3) * 7

2. Write the BASIC expression corresponding to each of the following algebraic expression:

(a) (x+y) 4

(b) 2x2 + 5x + 6

(c) x/y + y/z

(d) (x-y)4 / (x+y)4


This lesson is an introductory chapter on BASIC language. The purpose is to prepare you with the

basic rules of the language. The knowledge of these is essential for writing programs. The rules

described here pertain to standard BASIC. The GWBASIC or BASICA, which is going to be your

practical vehicle for learning this language however, an enhanced version of standard BASIC,

incorporating many additional features to add power to the language. It must however, be emphasized

that even if you stick to the rules of standard BASIC, it still remains completely valid for GWBASIC

or BASICA and can be run without any problem.

50


1. Define BASIC language along with its features.

2. Describe briefly the structure of BASIC language.

3. Differentiate between

(a) Numeric and String constant

(b) Arithmetical and Relational Expression

4. Write down the hierarchy of operations in Arithmetic Expression.

5. Define history of BASIC language briefly.


51

IN-TEXT QUESTION 1

1. (a) Commas are not allowed

(b) Two arithmetic operators +, - for the sign cannot be used simultaneously

(c) Exponent cannot contain a decimal point

(d) E must the followed by some integer number

(e) Negative sign should not be in the last

2. (a) correct

(b) correct

(c) correct

(d) correct

(e) Incorrect because quotation marks are not allowed in strings.

3. (a) 1230000

(b) 0.000015

(c) -300

(d) 5865696

(e) - 0.012

IN-TEXT QUESTION 2

1. (a) 2.5

(b) 49

2. (a) (x+y) ^4

(b) 2*x ^ 2 + 5*x + 6

(c) (x/y) + (y/z)

(d) (x-y) ^4 / (x+y) ^4

52

LESSON 25

FLOWCHARTING

25.1 INTRODUCTION

The flowchart is a means of visually presenting the flow of data through an information processing

systems, the operations performed within the system and the sequence in which they are performed. In

this lesson, we shall concern ourselves with the program flowchart, which describes what operations

(and in what sequence) are required to solve a given problem. The program flowchart can be likened

to the blueprint of a building. As we know a designer draws a blueprint before starting construction on

a building. Similarly, a programmer prefers to draw a flowchart prior to writing a computer program.

As in the case of the drawing of a blueprint, the flowchart is drawn according to defined rules and

using standard flowchart symbols prescribed by the American National Standard Institute, Inc.

25.2 OBJECTIVES

At the end of this lesson, you will be able to understand:

the meaning of flowchart

the basic parts of the flowchart such as flowchart symbols and the flow lines connecting

these symbols.

the advantages and limitations of flowchart

25.3 MEANING OF A FLOWCHART

A flowchart is a diagrammatic representation that illustrates the sequence of operations to be

performed to get the solution of a problem. Flowcharts are generally drawn in the early stages of

formulating computer solutions. Flowcharts facilitate communication between programmers and

business people. These flowcharts play a vital role in the programming of a problem and are quite

helpful in understanding the logic of complicated and lengthy problems. Once the flowchart is drawn,

it becomes easy to write the program in any high level language. Often we see how flowcharts are

helpful in explaining the program to others. Hence, it is correct to say that a flowchart is a must for

the better documentation of a complex program.

25.4 GUIDELINES FOR DRAWING A FLOWCHART

Flowcharts are usually drawn using some standard symbols; however, some special symbols can also

be developed when required. Some standard symbols, which are frequently required for flowcharting

many computer programs are shown in Fig. 25.1

Start or end of the program

Computational steps or processing function of a program

Input or output operation

53

Decision making and branching

Connector or joining of two parts of program

Magnetic Tape

Magnetic Disk

Off-page connector

Flow line

Annotation

Display

Fig. 25.1 Flowchart Symbols

The following are some guidelines in flowcharting:

(a) In drawing a proper flowchart, all necessary requirements should be listed out in logical

order.

(b) The flowchart should be clear, neat and easy to follow. There should not be any room for

ambiguity in understanding the flowchart.

(c) The usual direction of the flow of a procedure or system is from left to right or top to bottom.

(d) Only one flow line should come out from a process symbol.

or

(e) Only one flow line should enter a decision symbol, but two or three flow lines, one for each

possible answer, should leave the decision symbol.

Yes < 0 > 0

54

No = 0

(f) Only one flow line is used in conjunction with terminal symbol.

(g) Write within standard symbols briefly. As necessary, you can use the annotation symbol to

describe data or computational steps more clearly.

This is top secret data

(h) If the flowchart becomes complex, it is better to use connector symbols to reduce the number

of flow lines. Avoid the intersection of flow lines if you want to make it more effective

and better way of communication.

(h) Ensure that the flowchart has a logical start and finish.

(i) It is useful to test the validity of the flowchart by passing through it with a simple test data.

25.5 ADVANTAGES OF USING FLOWCHARTS

The benefits of flowcharts are as follows:

1. Communication: Flowcharts are better way of communicating the logic of a system to all

concerned.

2. Effective analysis: With the help of flowchart, problem can be analysed in more effective way.

3. Proper documentation: Program flowcharts serve as a good program documentation, which is

needed for various purposes.

4. Efficient Coding: The flowcharts act as a guide or blueprint during the systems analysis and

program development phase.

5. Proper Debugging: The flowchart helps in debugging process.

6. Efficient Program Maintenance: The maintenance of operating program becomes easy with the

help of flowchart. It helps the programmer to put efforts more efficiently on that part

25.6 LIMITATIONS OF USING FLOWCHARTS

1. Complex logic: Sometimes, the program logic is quite complicated. In that case, flowchart

becomes complex and clumsy.

55

2. Alterations and Modifications: If alterations are required the flowchart may require re-drawing

completely.

3. Reproduction: As the flowchart symbols cannot be typed, reproduction of flowchart becomes a

problem.

4. The essentials of what is done can easily be lost in the technical details of how it is done.

IN-TEXT QUESTIONS 1

1. Fill in the blank.

(i) A program flowchart indicates the_________ to be per formed and the __________ in which they

occur.

(ii) A program flowchart is generally read from _____________ to ________________

(iii) Flowcharting symbols are connected together by means of ___________________

(iv) A decision symbol may be used in determining the ____________ or ___________ of two

data items.

(v) __________ are used to join remote portions of a flowchart

(vi) ____________ connectors are used when a flowchart ends on one page and begins again on

other page

(vii) A ________ symbol in used at the beginning and end of a flowchart.

(viii) The flowchart is one of the best ways of ________ a program..

(ix) To construct a flowchart, one must adhere to prescribed symbols provided by the __________

.

(x) The programmed uses a ____________ to aid him in drawing flowchart symbols.

25.7 FEW EXAMPLES ON FLOWCHARTING

Now we shall present few examples on flowcharting for proper understanding of this technique. This

will help in student in program development process at a later stage.

Example 1

Draw a flowchart to find the sum of first 50 natural numbers.

Answer: The required flowchart is given in Fig. 25.2.

56

START

NO

YES

Fig. 25.2 Sum of first 50 natural numbers

Fig 2.2 Flowchart for computing the sum of first 50 natural numbers.

57

SUM = 0

N = 0

N = N + 1

SUM = SUM + N

IS N=50?

PRINT SUM

END

Example 2

Draw a flowchart to find the largest of three numbers A,B, and C.

Answer: The required flowchart is shown in Fig 25.3

YES NO YES YES

NO NO

Fig 25.3 Flowchart for finding out the largest of three numbers

58

START

READ A, B, C

IS B>C

?

IS A>B

?

IS A>C

?

PRINT B

PRINT C PRINT C PRINT A

END

Example 3

Draw a flowchart for computing factorial N (N!)

Where N! = 1 2 3 …… N .

The required flowchart has been shown in fig 25.4

Answer:

NO

YES

Fig 25.4 Flowchart for computing factorial N

59

START

READ N

M = 1F = 1

F = F * M

IS M=N?

PRINT F

END

M=M+1

Example 4

A company’s salesmen are selling toothpaste and tooth powder. The company having 50 salesmen

gives 10% commission on the sale of toothpaste and 20% commission on tooth powder.

Draw a flowchart to compute and print the total sale and the total commission for each salesman.


Note:

S = Salesman number

P1 = Amount of sales of paste

P2 = Amount of sales of powder

K = Counter for the number of salesman

Fig 25.5: Flowchart for Computing Commission on Different Items

60

Example 5

Modify the flowchart in Example 4 to print the following heading.

Salesman No Total Sale Total commission

Under these heading, write the values of these variables for the 50 salesmen. At the end, the totals of

the entire sale and the entire commission should also be printed out.


Note:

TS = Total sales

TC = Total commission

61

Fig: 25.6 Flowchart for writing proper heading and its contents

IN-TEXT QUESTION 2

1. What are name and the use of the following symbols?

(a) (b) (c) (d) (e)

2. Define Flowcharting.


In this lesson, we have discussed the advantages and limitation of flowcharting. We have also shown

some examples of flowcharting. This will help the students in learning this technique easily.


1. Draw a flowchart to read a number N and print all its divisors.

2. Draw a flowchart for computing the sum of the digits of any given number

3. Draw a flowchart to find the sum of given N numbers.

4. Draw a flowchart to computer the sum of squares of integers from 1 to 50

5. Draw a flowchart to arrange the given data in an ascending order.


IN-TEXT QUESTIONS 1

1. ( i ) Operations, sequence

(ii) Top, down

(iii) Flow lines

(iv) Equality, inequality

(v) connectors

(vi) Off -page

(vii) Terminal

(viii) documenting

(ix) ANSI (American National Standards Institute)

(x) Flowcharting template

IN-TEXT QUESTIONS 2

1. Symbol Name Use

62

(a) input/output To represent input of data for processing

or output of processed information.

(b) Terminal To indicate start or end of a program

(c) Decision marking To make logical construction to check some

condition.

(d) Process To represent an operation or a set of operation

(e) Connector To link one part of flowchart to another

2. Flowcharting is a technique of showing logical flow of data in pictorial form and integration

of programming steps for solving a given problem.

63

LESSON 26

INPUT/OUTPUT AND PROGRAM CONTROL STATEMENTS

26.1 INTRODUCTION

In the previous lesson, we studied about the constants, the variables and the arithmetic operation used

in the BASIC language. We also saw how these constants, variables and the arithmetic operations

may be combined to form expressions and statements. Now we shall learn how the complete program

in BASIC language can be written using the basic principles we have learnt so far.

For a computer program to be executed using a computer, we should give some values to the

computer. Once the computer, completes the required computation work, we should ask the computer

to produce the results in a proper format that can be understood by the common man. The

INPUT/OUTPUT statements of the BASIC language achieve these two important functions. Besides

these we shall also discuss the use of repetitive and branching statements used in BASIC language.

26.2 OBJECTIVES

At the end of this lesson, you should be able to:

understand clearly the use of INPUT/OUTPUT statements such as LET, READ-DATA,

INPUT, PRINT, PRINT USING etc.

learn the use of LOOPING and CONTROL statements.

develop BASIC programs using the various basic commands offered by the language

26.3 INPUT-OUTPUT STATEMENTS

It should be always kept in mind that computer cannot do anything by itself. It will act according to

the instructions supplied to it by the user. To achieve the required output in the desired format, a user

has to provide correct data and a series of processing instructions in proper order. In this section, we

will discuss various input/output statements provided in BASIC language.

26.3.1 Getting Data into Memory

As stated earlier, one of the basic features of a programming language is the input/output facility

offered by it. BASIC offers three such kinds of input statements. They are LET, INPUT and READ-

DATA. These statements are basically used to assign values to various variables.

26.3.2 LET Statements

Syntax:

Line number LET (variable name)=(Constants or Variables or expression)

Example of LET statement

64

10 LET X =5.32 ---> This is numeric constant

20 LET A = 6+9/3.2--> This is an arithmetic expression

30 LET Y = X+A --> This is also an arithmetic expression

40 LET I = 2-->numeric constant

50 LET I =I+Y -->I and Y are variable names

60 LET A$ = "NEW DELHI”--> String variable

70 LET F$ = "99983" -->String variable

80 LET A = B--> numeric variable

These are all valid LET statements. The value of the variable on the left hand side of the equal to sign

is assigned the value given in the right hand side of the equal to sign

EXAMPLE

15 LET A =10

25 LET B =5

35 LET A = A+B

The example shows A is the variable name, which is, assigned the value 10 and B is the variable name

assigned the value 5. In the memory the line number 15 gives an instruction by which A will be the

address or name of a cell/location where the value 10 will be stored. Similarly B will be name or

address of a cell/location where 5 will be stored. Line number 35 instructs that the values in the

address A and B be added and the resulting value be kept at the cell/location whose address is A.

Memory location Memory location

A B

Execution of line 15 10 Not known

Execution of line 25 10 5

Execution of line 35 15 5

Note here that after execution of line 15 it has been shown “Not known” in location B, because in this

program we have not given any value to the variable name B on line number 15. It's value is given in

65

the next line number 25. Since variable A has been already given the value 10 that continue to stay in

A until we assign a different value to A which replaces the earlier value. So in the next line number

35, A+B the values of A and B given before are added and put in the location A Now the latest value

of A is 15 and that of B will remain as 5. Let us suppose that line 35 has been replaced as

35 LET C = A + B

Here computer will add the values of A and B, i.e. 15 and put it in a third location C.

Location A Location B Location C

Line number 15 10 Not known Not known

Line number 25 10 5 Not known

Line number 35 10 5 15

26.3.3 INPUT Statement

Syntax

Line number INPUT Variable,List...

EXAMPLE

12 INPUT A,B,X

16 INPUT A$,F$,N$

20 INPUT Y1,F$,C2,NB

Whenever computer reads a line with the keyword INPUT it displays a sign? on the VDU and waits

for the data. We have to give the values of the variable at this prompt through the keyboard.

26.3.4 READ-DATA Statement

The LET and INPUT statement have certain limitations. By a LET statement we can assign one value

for each variable and if we have to get 10 values for 10 variables we have to use 10 statements with

LET. Also if a value is assigned through a LET statement its value can be changed only by replacing

that assignment statement by another assignment statement. In case of an input statement, the data is

provided at the prompt at execution time. If there is a large amount of data to be processed, it is

inconvenient to key in the entire data during the execution of the program. In such cases READ

statements are found useful. READ statement will always have a DATA statement along with it.

Syntax

Line number READ Variable, List....

Line number DATA Constant, List....

Example of a READ....DATA Statement

66

1 REM PROGRAM EXPLAINING READ....DATA STATEMENT

5 READ X2,Y,Z1,K

9 READ A,B3, C4, L

22 DATA 8,9,13,15,16,51,30,92

30 END

When the machine encounters the line number 5 with the READ statement followed by the variables

X2,Y,Z1,K it will collect from the DATA statements the values for these variables in the same order.

A one-to-one correspondence exists in READ-DATA statement, i.e. X2=8, Y=9, Z1=13, K=15.

In the next READ statement in line number 9 we have four more variables A,B3,C4,L.

These values will follow in the same order and one-to-one correspondence after the earlier READ

variables values, i.e., after 8,9,13,15, i.e., A=16, B3=51, C4=30, L=92.

Since all the values in the DATA here are exhausted, another i.e. third, READ statement cannot be

used until another DATA statement is included or more DATA is included in the above DATA list in

line number 22. A DATA statement can be anywhere in the program but must be before the END

statement. It is a normal practice to keep all DATA statements together at the end of the program

before END statement, so that in case you want to alter any data at the end it will be easy.

26.3.5 DATA BLOCK

The BASIC organises the contents of all the DATA statements into a data block. When the READ

statement are executed a pointer moves along with data block starting from the first element:

EXAMPLE

1 READ X1, Y1, Z1

7 READ N, M, L, K

12 READ A

19 READ X,Y

24 DATA 122

26 DATA-35,49, -101

28 DATA -691,81

30 DATA 8,10.-5,5

40 END

DATA BLOCK

Value Pointer Variable

122 <--- X1

-35 <--- Y1

67

49 <--- Z1

-101 <--- N

-691 <--- M

81 <--- L

8 <--- K

10 <--- A

-5 <--- X

5 <--- Y

Now look at the following some examples where all the programs do exactly the same work.

(a) 10 DATA "RAMA","DELHI",100,200,300

20 READ A$,B$,A, B, C

30 - - - - -

40 - - - - -

- - - - - - - - - - - - - -

80 END

(b) 10 READ A$,B$

20 READ A,B,C

30 - - - - - -

40 - - - - - -

60 DATA "RAMA","DELHI"

70 DATA 100,200,300

100 END

(c) 10 DATA "RAMA","DELHI"

20 DATA 100

30 DATA 200

40 DATA 300

50 READ A$,B$

60 READ A,B,C

- - - - - - - - - - - - -

100 END

(d) 10 READ A$

68

20 READ B$,A,B,C

30 DATA "RAMA"

40 DATA "DELHI"

50 DATA 100,200,300

- - - - - - - - - - - - -

100 END

In all these cases A$ is assigned the value RAMA and B$ the value DELHI.All the numeric variables

A,B,C are assigned the values 100,200,300 respectively.

So we note that for READ....DATA statement we should follow the following

There could be any number of READ and DATA statements.

As many variables are read by READ statement, at least the same number of values should be

there in the DATA statement. It may be more. If the number of values in DATA is less, then

there will be an error message OUT OF DATA given by the computer.

The type of variables (i.e., numeric, string) in the READ statements containing many

variables.

Although normally we keep all the DATA statements at the end of the program just before

END statement, DATA statement can occur anywhere in the program but before END

statement.

26.3.6 Restore Statement

The RESTORE statement beings the pointer to the first value of the DATA statement regardless of

the current position of the pointer.

Syntax

Line number RESTORE

For example,

10 RESTORE

The RESTORE statements may be used anywhere in the program, of course, before the END

statement.

The following example will clearly illustrates the use of RESTORE statement

10 READ X,Y

20 DATA 10,12,-7,,3.2, "PANKAJ"

30 RESTORE

40 READ A,B,C,D,N$

50 END

When the statement number 10 is executed, the variables X and Y are assigned the values of 10 and

69

12, the position of the pointer at this stage is shown below:

10 12 -7 3.2 "PANKAJ"

(Pointer)

(Position of pointer before execution of RESTORE statement)

When the statement 30 RESTORE is executed, the pointer is brought back to the first data value of

data statement as shown below:

10 12 -7 3.2 "PANKAJ"

( Pointer)

Now, the execution of the statement number 40 against the value to A,B,C,D and N$ will be as

shown below:

A 10

B 12

C -7

D 3.2

N$ PANKAJ

The RESTORE statement can be used in the following forms also:

Statement number RESTORE *

and

Statement number RESTORE $

If the key word RESTORE is followed by asterisk (*), then only numeric pointer is reset as shown in

the previous example. However, if the key word RESTORE is followed by a dollar sign ($), then only

string pointer is reset to the first string data. The simultaneous use of both asterisk (*) and dollar sign

($) is not allowed.

For example, if a BASIC program contains the following statements,

10 READ A,B,N$,M$

20 - - - - - - -

30 - - - - - - -

40 RESTORE *

70

50 READ P,Q,A$,B$

60 - - - - - - -

70 - - - - - - -

80 DATA 5,8,"DINESH",UPMA",10,12,"RAJESH","SANJU"

90 END

When the statement 10 is executed, A,B are assigned values 5 and 8 whereas the variables N$ and M$

are assigned the values DINESH and UPMA respectively. The execution of statement 40, restores the

numeric pointer to the first numeric value in the DATA statement i.e. to the value 5. The execution of

the statement 50, assigns the value 5,8, RAJESH and SANJU respectively to the variable P,Q,A$ and

B$. The values DINESH and UPMA are being ignored. Similarly, the execution of RESTORE$ can

also shown by taking similar example.

Consider another example

10 READ A,B,N$,M$

20 RESTORE $

30 READ P,Q,A$,B$

40 DATA 5,8, "DINESH", "UPMA", 10,12,"RAJESH",SANJU"

50 END

Here the statement RESTORE$ is used. The values assigned to the variable A,B,N$ and M$ are same

as in the previous example. However, when statement 20 is executed, the string pointer is reset to the

first string data namely DINESH. The execution of the statement 30 would assign the values 10 and

12 to the variables P and Q and then the pointer moves back-ward to assign the values DINESH and

UPMA to the variables A$ and B$

26.4 PRINT STATEMENT

The PRINT statement of BASIC provides limited methods of controlling the alignment and spacing of

printout in terminals. The general from of the PRINT statement is

Line number PRINT (Variable) separator (variable) separator or item......

The separation may be comma (,) or semicolon (;)

26.4.1 The Semicolon (;) Control

Program

10 LET S =1175.50

20 PRINT "TOTAL SALARY =";S; " RUPEES"

71

30 END

The output of the program 1 will be as

T O T A L S A L A R Y = 1 1 7 5 . 5 0 R U P E E S

Using semicolon in a print statement, the items are close to each other, and as a result more items can

be printed in one line,

26.4.2 The Comma (,) Control

100 PRINT "NUM","TEMP","SIZE", REMARK"

110 PRINT 65,-15.56,36,34

These two lines will be printed as follows

1 17 33 49 65 85

Zone 1 Zone 2 Zone 3 Zone 4 Zone 5

NUM

65

TEMP

-15.56

SIZE

36

REMARK

34

The number of columns in each zone may be checked from the literature of manual for the given

computer.

26.4.3 Print Using Statement

The PRINT USING statement is included in most versions of microcomputer BASIC. It allows

printed output to be formatted, giving the appearance of each data item. This PRINT USING

statement can specify both string and numeric data.

There are several different ways to format. The most commonly used are given below:

100 PRINT USING "##. ##"; A,B,C,

Line number PRINT USING Format String Numeric Variables

The format string "##. ##", which a numeric field containing a decimal point with not more than two

digits on each side.

What will be the output of the following program?

10 LET A =17.32

20 LET B = -5.38

30 LET C =40

40 PRINT USING "##. ##",A,B,C,

50 END

OUTPUT

72

17.32 -5.38 40.00

If string values are used instead of numeric values, the format string for PRINT USING will be as

follows:

100 PRINT USING "!!!!!!" ; N$

If N$ ="UNITED"

Then the above PRINT USING statement will give output as:

UNITED

Observe, there are six alphabets and we have used six exclamation sign (!). Each exclamation sign (!)

is used to represent each character of a string.

Note: Some computers use # for presenting a character.

Example

If N$ = "FROG" then

(a) 100 PRINT USING "!!!!";N$ gives output as bbFROG

(b) 100 PRINT USING ">!!!!!!";N$ gives output as

(> character is used for the right justification of a string.)

Since "!!!!!!" has six character representations and FROG has only four characters,">" sign gives

characters b b in the left side as the PRINT USING with > gives right justified. Space characters (b

b ) are used to fill left space.

With the same explanation

100 PRINT USING “<!!!!!!”; N$ gives output FROG b b

(< is for left justified), Left justified space filled to right.

Note: b is used as space character.

26.4.4 TAB FUNCTION

The TAB (abbreviation of TABULATION) function is a very important function because it enables

the user to exercise exact control over the print positions. The use of a COMMA and a SEMICOLON

to space out the output is not so flexible as the TAB function.

TAB (n) moves the printer head to the nth column and printout of any data starts from that column.

Syntax:

Line number PRINT TAB (N); X

Where N is a positive number, a variable or an expression having positive value and X shows output

data

The execution of TAB function is explained below:-

(a) If N is an integer, the printer head moves to the Nth column and printing of the value of X starts

73

from that column

(b) In case N is a variable, not having the internal value, it is rounded and the printer head moves

according to this value.

For example, 5 X = 12

10 K = 5.3

20 PRINT TAB(k) ; X

(c) On the other hand, if N is an expression then first of all, the expression is evaluated and rounded, if

necessary. The printer head move based on the value of this expression.

The backward movement of the printer head is not allowed.

For example, consider the statement

10 PRINT TAB (25); "DINESH"; TAB(20); "RAJESH"

Here TAB (25) instructs the computer to start printing DINESH from column number 25 onwards.

Then TAB (20) instructs the computer to write RAJESH from column 20. Since the printer head is

already beyond the column 20 and backward movement is not allowed, so TAB (20) is ignored and

the output is same as if TAB (20) was not present. The above statement is equivalent to

10 PRINT TAB (25); "DINESH"; "RAJESH"

Consider another example, where TAB function is ignored

20 PRINT "10.3", TAB (10); "15.6"

The comma preceding the function TAB (10) Positions the printer head to the column 16 so that the

function TAB (10) becomes redundant as printer head cannot move backward and hence it is ignored.

The value 15.6 will be printer from column 16 onwards.

The use of TAB function is an elegant method to prepare patterns, producing tables and to plot graphs

etc.

26.5 PROGRAM CONTROL STATEMENTS # # THEIR SYNTAX AND USE

We have already seen a few BASIC statement like REM, (in Lesson 1),and

LET,INPUT,READ,DATA etc in this Lesson itself. The other few BASIC statements and their

explanations are given in this section. We will discuss them in details using different program.

26.5.1 Unconditional Go To Statement

GOTO statement is used to transfer control from a statement, say S1 to another statement, say S2,

generally, S2 does not follow S1 immediately in sequence.

Syntax: Line number GO TO n

n is the line number of the statement where control will be transferred.

74

Program 1

10 READ A,B,X,Y

20 GO TO 60

30 LET X = X*X+A

40 LET =Y*Y +B

50 PRINT X, Y

60 LET X =A*X

70 LET Y =B*Y

80 PRINT X,Y

90 DATA 6,3,4,5

100 END

This shows after reading the values of A,B,X,Y, in line number 10, the control jumps to line number

60 and calculate X =A*X, Y =B*Y then prints X,Y in line number 80 and ends the program. Line

number 30,40,50 are never executed. If we want to execute 30,40,50 then our program will add few

more jump statements, i.e. few more GO TO statements.

Consider the following program 2.

Program 2

10 READ A,B,X,Y

20 GO TO 60

30 LET X =X*X+A

40 LET Y =Y*Y+B

50 PRINT X,Y

55 GO TO 100

60 LET X =A*X

70 LET Y =B*Y

80 PRINT X,Y

85 GO TO 30

90 DATA 6,3,4,5

100 END

Thus by introducing line number 55 and 85 all the statements are executed. So line number 30 and 40

prints X =X*X +A (value), Y =Y*Y+B (value) and line number 80 prints X = A*X and Y =B*Y

75

IN-TEXT QUESTION1

1. Fill in the blanks

(a) In the LET statement, the value of a variable on the ......... hand side of the equal to sign is

assigned to the variable given in the .......... hand side of the equal to sign.

(b) READ statement cannot be used without a ........... statement.

(c) DATA statement can occur anywhere in the program, but must be before the ........... statement.

2. State the difference between READ and INPUT statement?

3. What is the use of PRINT USING statement?

4. What is the use of RESTORE statement?

5. Define briefly the use of TAB function.

26.5.2 The Branching Statement IF... THEN

The IF...THEN is a decision making statement, depending upon the decision, it can change the order

of execution.

It helps the computer to check whether a relation is TRUE or FALSE.

Syntax: Line number IF (relational expression) THEN n where n is a line number or an instruction

itself.

If the relation expression is true then n will be executed otherwise the statement following this

IF...THEN statement will be executed.

EXAMPLE 2

Evaluate the expression Y =X2 for X =1,2,3...

Program 1

10 LET X = 1

20 LET Y = X*X

30 PRINT Y

40 LET X = X+1

50 GO TO 20

60 END

In this process we see each time the line number 50 is executed the control is transferred to line

number 20 unconditionally. Thus we have an infinite loop which is never ending.

Computer goes round and round and never reaches END

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To stop the infinite loop we can add a condition, i.e. say if X is greater than or equal to 31 (X >=31)

then the program ends otherwise it keeps on printing the value of expression Y = X2 for X =1,2,3....30.

Program 2

10 LET X = 1

20 LET Y = X*X

30 PRINT Y

40 LET X = X+1

50 IF X> = 31 THEN 70

60 GO TO 20

70 END

Thus we see that IF-THEN is one of the powerful statements which can stop or get the computer out

of an infinite loop.

EXAMPLE 3

Problem 1

Write a program to find out the auto fare depending on the Kilometers traveled. The minimum fare

charged is Rs. 3.00. This minimum fare remains for 2 kms or less of travel. After 2 kms, the charges

are 75 rp per kilometer.

Program 1

10 INPUT "KILOMETER", K

20 IF K < = 2 THEN PRINT "RS.3” : END

30 LET CHARGE =3+ (K-2) *.75

40 PRINT CHARGE

50 END

Here in line number 20, if K is less than or equal to 2 (i.e., K<=2) then it will print Rs. 3 and (: END)

means END, in continuation to the line number 20 next statement is END.

Otherwise if K is not less than or equal to 2 then line number 30,40 then 50 will be executed.

26.5.3 The Branching Statement IF...THEN...ELSE

Another important statement is IF ...THEN...ELSE.

Syntax:

Line number IF (condition or relational expression)

THEN (line number or Instruction)

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ELSE (line number or Instruction)

The IF...THEN...ELSE statement is a decision making statement as it decides the path of the program.

It helps in making comparisons and testing whether a condition is true or not.

IF is always followed by a valid BASIC condition or expression. If the condition is found true then

the line number or Instruction after THEN is performed otherwise line number or instruction after

ELSE is performed.

EXAMPLE 4

Problem 1

Ages of different students appearing in the Board examination are taken. If the age is below 17 the

student is not eligible, otherwise he can appear in the Board examination. We are asked to write a

program for this problem.

Program 1

10 INPUT “AGE”; A

20 IF A>= 17 THEN 30 ELSE 50

30 PRINT “WELCOME FOR BOARD EXAMINATION”

40 GO TO 60

50 PRINT “YOU ARE NOT ELIGIBLE FOR BOARD EXAM.”

60 INPUT “WANT TO INPUT AGAIN (Y/N)”; Y$

70 IF Y$ = “Y” THEN 10

80 END

The line number 10 will cause the message in screen AGE? We input the age through the keyboard,

say 18. Line number 20 tests whether A>17 or not. Since A=18>17 line number 30 is executed.

Line number 30 prints WELCOME FOR BOARD

Line number 40 causes the control to pass to line number 60.

Line number 60 causes the message WANT TO INPUT AGAIN (Y/N)? We input either Y or N.

In line number 70 if input is Y then control goes to line number 10. Otherwise if input is N then

control goes to the line number 80 i.e. END.

Now if in line number 70 we input Y then control will pass again line number 10, we give another

age, say 13

In line number 20 value of A (i.e. 13) is not greater than 17, therefore ELSE part will be executed and

control will go to line number 50. Line number 50 will print YOU ARE NOT ELIGIBLE FOR

BOARD EXAM. Then line number 60 as before will be executed. In this way a large number of

students age can be tested. When we want to stop we should input N in line 60 for Y$.

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Problem 2

10 INPUT A,B,C

20 IF A>B AND A>C THEN 50 ELSE 30

30 IF B>A AND B>C THEN 60 ELSE 40

40 IF C>A AND C>B THEN 70

50 PRINT "A IS THE LARGEST NUMBER": GO TO 80

60 PRINT "B IS THE LARGEST NUMBER": GO TO 80

70 PRINT "C IS THE LARGEST NUMBER"

80 INPUT "WANT TO INPUT AGAIN (Y/N)" ; Y$

90 IF Y$ = "Y" THEN 10

100 END

In line number 20,30,40 comparisons are made among the values of A,B, and C.

AND is a logical operator which combines A>B and A>C. If both the relational expression preceding

and following AND are true then the line number following THEN will be executed otherwise if one

of the relational expression, A>B or A>C is true then the line number following ELSE will be

executed. Same procedure follows for the next two IF statements also.

If expression at 20 is found true, the line number 50 will print A is THE LARGEST VALUE and then

GO TO 80 will be executed as the next statement to line number 50. If it is found false the control

passes to statement 30 and the expression at that statement is checked. This part of the program can

also be written as follows:

50 PRINT "A IS THE LARGEST NUMBER"

55 GO TO 80

60 PRINT "B IS THE LARGEST NUMBER"

65 GO TO 80

Thus line number 50 and 60 in earlier program of problem 2 is equivalent to line numbers 50,55,60,65

in the above program statement.

Syntax: For IF...THEN...ELSE with AND is given as;

IF (Condition 1 or Relational expression) AND (Condition 2 or Relational expression) THEN

(Instruction 1) ELSE (Instruction 2)

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Like AND another logical operator is OR.

Syntax: for IF…. THEN...ELSE with OR is:

IF (Condition 1 or Relational expression) OR (condition 2 or Relational expression)

THEN (Instruction 1) ELSE (Instruction 2)

This means if either of the conditions (or relational expression) followed or preceded by OR is true

then the instruction 1 is executed. If neither of them is true then instruction 2 is executed.

26.5.4 The Looping Statement FOR-TO...NEXT

We have already seen that a loop can be built in BASIC by using the IF-THEN and GOTO

statements.

When it is known in advance how many times the loop must be repeated the statement FOR-

TO...NEXT is the most effective statement.

A loop is built up by FOR-TO and ended by NEXT.

Syntax:

Line number FOR I = M TO N STEP J

Loop - - - - - -

- - - - - -

Line number NEXT I

The numeric variable name following FOR is called the control variable or loop variable.

M and N are numeric constants where M gives the initial or starting value of the loop and N gives the

final value, J followed by keyboard STEP gives the increment in M till N is reached. The increment

can be negative also.

M,N,J can be numeric variable names. In such cases their numeric values should be assigned before

the starting of the loop, i.e. before coming to FOR-TO statement.

They key word NEXT should have the same control variable I followed by it. Thus one loop can be

started with FOR-TO and ended with NEXT.

Inside one FOR-TO ...NEXT loop there can be more FOR-TO...NEXT loop. But once a FOR-

TO...NEXT is inside another FOR-TO...NEXT, it should remain completely inside the former loop.

Such FOR-TO...NEXT loops are called Nested loops. In the absence of the STEP clause, the

increment is assumed to be 1.

EXAMPLE 5

Problem 1

80

Suppose we want to print the output in the following format:

* * * * *

* * * *

* * *

* *

*

Program 1

10 FOR S=5 TO 1 STEP-1

20 FOR X=1 TO S

30 PRINT "*" ;

40 NEXT X

50 PRINT

60 NEXT S

70 END

This program contains two loops: the outer loop is from the line number 10 to 60 and inner loop from

line numbers 20 to 40. In line number 10, initially S is assigned a value 5. Since the value of S is

greater than 1, control is transferred to line number 20, which causes the inner loop to execute 5 times

resulting into printing of 5 stars (*) in one row. The statement at line number 50 will transfer the

printer control to the beginning of the next line. When line 60 is encountered, the control goes back to

line number 10. Now the value of S becomes 4 and once again the inner loop is executed 4 times

resulting in printing of 4 (*) stars in second row. This process will continue till the value of S

becomes 1. After that it will come to end.

Problem 2

Suppose we want to sum to following series:

1,2,3,4_ _ _ _ 100.

Program 2

10 LET S=0

20 FOR I=1 TO 100

30 LET S=S+I

40 NEXT I

50 PRINT " SUM OF SERIES =" ; S

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60 END

26.5.5 The Multiple Branching Statement ON... GOTO

The GOTO statement allows only one transfer point, IF...THEN allows two transfer points, the

ON...GOTO can have more than two transfer points, thus providing multiple branching facility.

Syntax: line number ON (Numeric variable or expression) GOTO n1,.n2,n3,..

The expression is a valid BASIC expression and n1,n2,n3,.... are the statement numbers or line

number where the control will be transferred.

If ON is followed by numeric variable name and if the value of numeric variable is 1 control is

transferred to n1, if 2 then n2, if 3 then n3 and so on.

If ON is followed by an expression by an expression then it is evaluated and truncated to an integer

value. Control is transferred in the same manner as discussed above.

If the integer value is less than or more than number of line numbers present in the list then an "OUT

OF RANGE" error message will be given by the computer.

EXAMPLE 6

Problem

Write a program to add, subtract, divide and multiply two numbers A and B.

Program

5 INPUT A,B

10 INPUT " 1-ADD, 2-SUB, 3-MUL, 4-DIV"; N

20 ON N GOTO 30,40,50,60

30 PRINT A+B : END

40 PRINT A-B : END

50 PRINT A*B : END

60 PRINT A/B : END

When line 5 is executed, there will be question mark (?) then you have to input the values of A and B

through keyboard. Line number 10 will cause a message on the screen 1-ADD, 2-SUB, 3-MUL, 4-

DIV and then display of question mark (?) for N.

If we input through keyboard 1 then N takes the value 1.If we enter 2 or 3 or 4,N will take 2 or 3 or 4

accordingly. If the value of N is

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1 control is transferred to 30,



4 control is transferred to 60

On execution of line number 30 addition of A and B will be displayed on the screen and program will

come to an end. Similarly, in line number 40,50,60 printing of the result of subtraction, multiplication

and division will be displayed respectively.

IN-TEXT QUESTIONS 2

1. Write a LET statement for each of the following:

(a) To assign the value 5.2 to the variable A

(b) To assign the string PENTIUM-SYSTEM TO the variable B$

(c) To assign the value of the variable C to the variable D

(d) To increase the value of the variable E by 1

(e) To assign the value equal to three times the value of the variable P to the variable Q

2. In the following FOR statements, write the values taken by the control variable

(a) 10 FOR L = 3 TO 12 STEP 2

(b) 20 FOR M = 1 TO 50 STEP 10

(c) 30 FOR N = 100 TO 0 STEP -20

(d) 40 FOR K = 5 TO 5

(e) 50 FOR I = 10 TO 6 STEP -1

3. Give the output of the following short program

10 PRINT "PANKAJ" , "GOEL"

20 PRINT "PANKAJ" ; "GOEL"

30 PRINT "PANKAJ",, "GOEL"

4. Give the output of the following short program

10 LET A = 40

20 LET B = 50

30 LET C = 60

40 LET D = A+B+C

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50 PRINT “A= A”; A “B = B”; B “C=”; C, “D=”; D

60 END


This lesson gives us the introductory features of BASIC language, which are very essential for writing

small programs in BASIC. Some additional statements and functions of BASIC will be discussed in

Lesson 4. The example programs given in this lesson should be run on a computer so that the concept

is clear before going to the next lesson.

26.7 TERMINAL QUESTION

1. What does an unconditional GOTO statement do?

2. What is the difference between an IF... THEN statement and an IF... THEN... ELSE statement?

3. How is the multiple branching facility provided in BASIC?

4. Write a program in BASIC using For-Next loop to get the following output:

1 * * * *

2 * * * * * * * * * *

3 * * * * *

4 * *

5 * * * * * * *

5. Write a program in BASIC to print out the largest number out of 10 given numbers.

26.8 FEEDBACK TO IN-TEXT QUESTION

IN-TEXT QUESTIONS 1

1. (a) Right, Left

(b) DATA

(c) END

2. In case of an INPUT statement, data is read from the keyboard at the time of execution of the

program. In READ statement, data is provided in the program itself through a DATA statement.

3. Print using statement allows printed output to be formatted corresponding to the given

specification.

4. The restore statement brings the pointer to the first value of the DATA statement, regardless of

the current position of the pointer.

5. TAB function enables the user to exercise exact control over the print positions.

IN-TEXT QUESTIONS 2

1. (a) 10 LET A = 5.2

(b) 20 LET B$="PENTIUM-SYSTEM"

(c) 30 LET D = C

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(d) 40 LET E = E+1

(f) 50 LET Q =3*P

3 (a) Values taken by L are : 3,5,7,9,11

(b) Values taken by M are : 1,11,21,31,41,

(c) Values taken by N are : 100,80, 60,40,20,0

(d) Value taken by K is : 5

(e) Values taken by I are : 10,9,8,7,6,

4. PANKAJ GOEL

PANKAJ GOEL

PANKAJ GOEL

5. A= 40 B= 50 C= 60 D =150

LESSON 27

HANDLING OF ARRAYS, FUNCTIONS AND SUB-ROUTINE

27.1 INTRODUCTION

In the previous lesson, you have gone through the programming technique and various

INPUT/OUTPUT and control statements in BASIC. But the features that make this programming

language more useful are use of subscripted variables, subroutine and various functions provided to

help the programmer. We shall be discussing all these features in this lesson. We have also included

various sample programs, which will help you further in writing more complex programs in BASIC

language.

27.2 OBJECTIVES

This lesson will explain you about handling of lists, tables, subroutine, sub-programs and some of the

functions of BASIC. At the end of this lesson, you should be able to:

use functions and subroutines in BASIC language

write complex programs in BASIC language

learn how to set up and use arrays in BASIC programs

27.3 HANDLING LISTS AND TABLES (ARRAYS) IN BASIC

In all our programs so far, a single variable (one storage location in internal memory) has been

associated with each variable name. In this lesson, we will discuss the concept of an array: a

collection of variables, all of which are referenced by the same name. We will discuss one-

85

dimensional arrays (lists) and two-dimensional arrays (tables), concentrating on the former. Each item

of data in an array does not have a unique variable name, on the other hand, a group of similar data is

given one name. The smallest component of an array is called an element of the array.

Example 1: suppose we want to represent five numbers (10,12,42,91,7,) which represent the marks of

five students

Solution:

We can use an array name M(I) which is also called the subscripted variable and I is the subscript

which varies from 1 to 5. M is the name of array and M(1) is an element of the array M.

In the memory it is stored as,

M(I) Cells Quantities

M(1) 10

M(2) 12

M(3) 42

M(4) 91

M(5) 7

Problem1: Write a program to read the above data into the memory.

Program 1

10 DIM M(5)

20 FOR I = 1 TO 5

30 READ M(I)

40 NEXT I

50 DATA 10,12,42,91,7

60 END

Let us go back to the above example.

M is an array of 5 numbers 10,12,42,91,7, where under the array name M the five different elements

M(1),M(2), M(3), M(4), M(5), are given one subscript I. This M(I), with a single subscript I, is an

example of a one-dimensional array. Let us study a practical example of one-dimensional array.

Example 2: We have an item biscuit in a shop. We have prices for 10 different biscuits as 60, 45.5,

32.6, 19.5, 52, 49,53.75, 29, 43, 38.6. We write a program to print these different values or we want to

know the price of any type of the above biscuits. We will do it by using an array.

Solution

86

Since they are similar items, we give them a single name BISCUIT or in short BIS. Since we know

only one specification i.e. price we have a single subscript, say I. So the array is now BIS(I). Since

there are 10 prices for 10 types of biscuits I varies from 1 to 10 i.e. BIS(1), BIS(2)…….BIS(10).

If we want to know the price for the biscuit of type 4, we will print BIS(4) which will give us the

required price.

Program 2

10 DIM BIS(10)

20 REM PRICES FOR 10 TYPES OF BISCUITS ARE TO BE READ

30 REM THE 10 PRICES HAS TO BE PRINTED ALSO

\40 FOR I = 1 TO 10

50 READ BIS(I)

60 NEXT I

70 PRINT “THE PRICES OF TEN DIFFERENT BISCUITS”

80 FOR I =1 TO10

90 PRINT BIS(I)

100 NEXT I

110 DATA 60,45.5, 32.6, 19.5, 52,49,53.75

120 DATA 29,43,38.6

130 END

OUTPUT

Line number 70 will print

THE PRICES OF TEN DIFFERENT BISCUITS

Line number 90 due to line number 80 and 100 will print

60

45.5

32.6

19.5

52

49

53.75

29

43

38.6

87

The line number 10 DIM BIS(10) is compulsory. This informs the machine that we are giving an

array with single subscript having 10 elements. So, 10 cells in the memory location will be kept for

the variable name BIS.

If we want an array of strings instead of numeric value, see the following example:

Example 3

To store the names of six motor cars in any array (table) such as:

FORD MARUTI AMBASSADOR FIAT STANDARD VAUXHAL L

We can write a program as follows:

Program 3

10 REM DECLARE THE NAME AND SIZE OF THE TABLE

20 DIM C$(6)

30 REM… USE THE READ/DATA TECHNIQUE

40 REM TO STORE STRINGS

50 FOR J = 1TO 6

60 READ C$(J)

70 NEXT J

80 REM.. NOTE THE STRINGS USED AS DATA ARE

90 REM.. ENCLOSED BETWEEN QUOTATION MARKS

100 REM.. ARRAY NAME TO STORE STRINGS IS

110 REM.. GIVEN AN STRING VARIABLE NAME C$

120 DATA “FORD”, “MARUTI”, “AMBASSADOR”

130 DATA “FIAT”, “STANDARD”, “VAUXHALL”

140 END

The REM (i.e. remarks) given in the line number 30,40,80,90,100,110, explains the program.

Though DATA is given in two lines 120 to 130, the data should be in the order they are placed.

C$(1) = “FORD”

C$(2) = “MARUTI”

C$(3) = “AMBASSADOR”

C$(4) = “FIAT”

C$(5) = “STANDARD”

C$(6) = “VAUXHAULL”

88

Example 4

Let the 10 data values are given as 4, -6, 7, 2.3, - 6.1, 5. 3

-1, 0, - 2.7,9

WE give this set of values the name, say VAR (I) where I is the subscript.

If I = 1, then VAR (1) has the value 4

I = 5, then VAR (5) has the value -6.1

I = 8 then VAR (8) has the value 0, and so on.

The program for adding all the 10 numbers.

Program 4

10 REM ADDING 10 NUMBERS IN A ONE DIMENSIONAL TABLE

12 DIM VAR (10)

15 LET SUM = 0

20 FOR I = 1 TO 10

30 READ VAR (I)

40 LET SUM = SUM +VAR (I)

50 NEXT I

60 DATA 4, -6,7, 2.3, -6.1, 5.3, -1, 0, -2.7,9

70 PRINT SUM

80 END

27.3.1 The DIM Statement

When subscripted variables are used in a program, certain information about them must be supplied to

the computer before it is used. These are:

(a) Which variables are subscripted?

(b) What is the maximum size for each subscript?

DIM is the short form of DIMENSION.

By using this statement in line number 10 of the program 1 above, the array whose name is M has

been allotted 5 cells in the memory location. Syntax for the DIM statement is

Line number DIM array name (unsigned integer)

The unsigned integer specifies the size of the array variable.

If we write 10 DIM A(100), X(10), then 100 locations are reserved for the array name A and 10

locations for the array name X.

DIM should be the first statement in the program barring REM statement.

Problem 5

89

Suppose we want to read the roll number of a student and his marks obtained in five subjects in the

board examination. Now print the roll number and average marks secured by him.

Program 5

10 DIM M(5)

20 INPUT ROLLNO

25 LET TOT = 0

30 FOR I = 1 TO 5

40 READ M(I)

50 LET TOT = TOT + M(I)

60 NEXT I

70 LET AVERAGE = TOT/5

80 PRINT ROLLNO, AVERAGE

90 DATA 60,52,49,80,72

100 END

On the execution of line number 30, initially the control variable I becomes 1 and line number 40

reads M(I), i.e. the first mark from line number 90, that is 60 and adds to the variable TOT which is

initially zero. So for I = 1 line 50 gives TOT = 0 +60 = 60, control then goes to line number 60 and

back to 30. Now I becomes 2 and line number 40 reads M(2), i.e. 2nd marks from DATA, i.e. 52. In

line number 50 TOT = 60 + M(2), i.e. TOT = 60+52 = 112 and so on. So line number 30 to 60 is

executed five times. Thus finally in the variable name TOT we have TOT = 60+52+49+80+72=313.

So, when line number 70 is executed AVERAGE = 313/5 =62.6. Line number 80 will print the

ROLLNO which is entered in line number 20 and the average AVERAGE as 62.6.

If we want to do this process for a large number of students say 10 we have to give more data in

DATA statement, i.e. 45 more data values and put another loop to repeat the process for ten students.

Program 5(a)

10 DIM M (5)

15 FOR J = 1 TO 10

20 INPUT ROLLNO

25 LET TOT =0

30 FOR I = 1 TO 5

40 READ M (I)

50 LET TOT = TOT + M(I)

90

60 NEXT I

70 LET AVERAGE = TOT/5

80 PRINT ROLLNO, AVERAGE

85 NEXT J

90 DATA 60,52,49,80,72,98,69,72,80,75

100 DATA 88,61,54,48,60,52,92,86,81,65

110 DATA _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

120 DATA _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

130 DATA _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

140 END

IN-TEXT QUESTIONS 1

1. Given the following code:

10 LET S =0

20 FOR I = 1 TO N STEP 2

30 LET S = S+2*I-1

40 NEXT I

50 END

You are required to complete each statement.

(a) The accumulator is the variable ___________

(b) The control variable is _______________

(c) After execution, S contains the sum of the first N _________ Integers.

2. Correct the errors in each of the following program segments:

(a) 10 FOR K = 1 TO 5

20 FOR J = 1 TO K

30 PRINT K + J

91

40 NEXT K

50 NEXT J

(b) 10 LET S = 0

20 FOR I = 1 TO 10

30 LET S = S + I

40 PRINT S

50 NEXT K

3. What is the output of each of the following program segments?

(a) 10 FOR I = 7 TO 10 STEP 2

20 PRINT I;

30 NEXT I

40 PRINT I

50 END

(b) 10 FOR I = 1TO 10

20 IF I = 5 THEN 40

30 PRINT I + 1

40 NEXT I

50 END

27.3.2 Double-Subscripts or two-dimensional arrays

A subscripted variable name in BASIC can have up to three subscripts. The use of two subscripts has

very wide applications, especially manipulation of tables or any such things, which has rows and

columns both in it.

Example: Represent subscripted variable or two-dimensional array having name TABLE(I.,J) where I

indicates row and J indicates column.

Where, TABLE (I,J) = 2 4 8 10

1 3 5 7

3 7 13 17

Thus we see TABLE (I,J) has 3 rows, i.e. I = 1 TO 3 and 4 columns, i.e. J = 1 TO 4.

Problem 6

We want to read and print the values of TABLE (I,J) as given above

Program 6

92

10 DIM TABLE (3,4)

15 FOR I = 1 TO 3

20 FOR J = 1 TO 4

30 READ TABLE (I,J)

35 PRINT TABLE (I,J)

40 NEXT J

50 NEXT I

70 DATA 2,4,8,10,1,3,5,7,3,7,13,17,

80 END

See how it reads the data

TABLE(1,1) TABLE(1,2) TABLE(1,3) TABLE(1,4)

2 ---------> 4 --------> 8 ----------> 10


1 ---------> 3 --------> 5 ----------> 7


3 ---------> 7 --------> 13 ----------> 17

As the subscript J corresponding to the column is in the inner FOR loop, the table is read row-wise. J

being in the inner loop changes more frequently from 1 to 4 for every value of I, which is in the outer

loop. If we want to read the data column-wise program will be as follows.

Program 7

10 DIM TABLE (3,4)

20 FOR J =1 TO 4

30 FOR I =1 TO 3

40 READ TABLE (I, J)

50 NEXT I

60 NEXT J

70 DATA 2, 1, 3, 4, 3, 7, 8, 5, 13, 10, 7, 17

80 END

More applications relating to subscripted variables will be shown in the last section.

We have shown you to store numeric data in a table (array) with row and column subscripts.

93

Now, You will see how string data is stored in a two-dimensional array.

Example

The following are data values (names), which are to be stored in the table form with rows and

columns.

HARIOM DINESH RAJESH PANKAJ

BIMLA UPMA SANJU ANAMIKA

The program is as follows:

Program 7

10 REM DECLARE THE NAME AND SIZE OF THE TABLE

20 DIM N$ (2,4)

30 REM SET UP AN OUTER LOOP TO CONTROL THE ROW SUBSCRIPT

40 FOR M = 1 TO 2

50 REM…..SET UP AN INNER LOOP TO CONTROL THE COLUMN SUBSCRIPT

60 FOR P = 1 TO 4

70 REM .. USE A READ/DATA STATEMENT TO STORE DATA AS

80 REM .. SHOWN IN DIAGRAM

90 READ N$ (M, P)

100 NEXT P

110 NEXT M

120 DATA "HARIOM", "DINESH" "RAJESH"

130 DATA "PANKAJ", "BIMLA"

140 DATA "UPMA", "SANJU", "ANAMIKA"

150 END

IN-TEXT QUESTIONS 2

1. Determine whether each of the following statements is true or false.

94

(a) Array of string data and array of numeric data can be declared in the same DIM statement.

(b) All elements of an array must be of either string type or numeric type.

(c) One and two-dimensional arrays cannot be declared in the same DIM statement.

2. A two-dimensional array FAX has two rows and four columns

5 10 15 20

25 30 35 40

(a) What are the values of FAX (1,3) and FAX (2,1) ?

(b) Which elements of FAX contain the numbers 30 and 20 ?

3. What is displayed when the following program segment is executed?

10 DIM A (2,3)

20 FOR I = 1 TO 2

30 FOR J = 1TO3

40 LET A(I,J) = I+J+1

50 NEXT J

60 NEXT I

70 PRINT A(1,2); A(2,1); A(2,2)

80 END

4 Write a BASIC program that determines and prints the smallest and largest elements of a two-

dimensional array (assuming that it; has been already inputted) with four rows and five

columns.

5. Write a BASIC program to arrange the following numbers in an ascending order:

-71, -20, 14, 0, 5

27.4 FUNCTION AND SUBROUTINE

27.4.1 Defining a function---the DEF statement

To avoid repeated programming of the same set of calculations, the programmer would like to write

his or her own functions, which are similar to the Library functions. It may so happen that a particular

calculation or a set of calculations occurs more than once in the program. If the calculation can be

defined by a single statement then we use the function statement DEF FN.

Syntax: line number DEF FNV (a) = expression

Where “V” is the one-letter name of the function and "a" is the argument, which appears as a variable

in the expression on the right.

95

Problem 1

Suppose we want to write a program to calculate y for various values of x, say for x = 1,2,3,4,5, for

the expression y(x) =ax2 + bx + c

Program 1

10 DEF FNY (X) = A*X*X + B*X + C

20 INPUT A, B, C

30 FOR X = 1 TO 5

40 PRINT X, FNY(X)

50 NEXT X

60 END

On execution of the program line number 30 TO 50 will give the value of y(1) through y(5) for the

respective value of x, calculated at line number 10. The value of x is supplied in line number 30 and

values of A, B and C are input at line 20.

Problem 2

Let us consider the program to calculate

y = 1.5x + 3 for x<= 2

y = 2x + 5 for x>2

Program 2

100 DEF FNY(X)

105 INPUT X

110 IF X < = 2 THEN 140

120 LET FNY = 2*X + 5

130 GO TO 150

140 LET FNY = 1.5*X + 3

150 FNEND

170 PRINT X, FNY(X)

180 END

Here DEF FNY (X) statement in line number 100 is used without being equated to expression. The

FNEND statement in line number 150 indicates the end of the function. The line numbers 160 to 180

consist the main program. On execution of line 170 a call to the function FNY(X) is made causing the

execution of line number 100 to 150 with the input value of X.

96

The DEF statement must have DEF FN and variable name with one character and arguments included

in the parenthesis. Arguments can be more than one also. The argument is a variable, which must

appear in the right side after the equal to (=) sign, in case of DEF FN statement is equated to an

expression. (For example, see problem 1)

Example 1

Evaluate the algebraic formula z =(u/v + x/y)/2 for different set of values of u, v, x, y.

Solution

10 DEF FNZ(U,V,X,Y) =(U/V + X/Y)/2

20 INPUT U,V,X,Y

30 PRINT FNZ(U,V,X,Y)

40 END

This is for one set of values for U,V,X,Y. Now the program given below will evaluate the formula for

different set of values for U,V,X,Y

10 DEF FNZ (U,V,X,Y) = (U/V + X/Y)/2

20 INPUT U,V,X,Y

30 PRINT FNZ(U,V,X,Y)

35 IF U = O THEN 50

40 GO TO 20

50 END

Line number 40 sends the control back to INPUT. Now, you can enter another set of values for

U,V,X,Y. When you want to stop, you enter O for U. Then line number 35 will bring the program to

END.

Example 2

Define a function for subprogram for the algebraic formula

p = log(t2 -a) for t2 > a

log(t2) for t2 = < a

Solution

30 DEF FNP(T,A)

40 INPUT T,A

50 IF T * T < = A THEN 80

60 LET FNP =LOG (T ^ 2 -A)

97

70 GO TO 90

80 LET FNP = LOG (T ^ 2)

90 FNEND

100 PRINT T, A FNP (T,A)

110 END

In line number 40, the values of T,A can be input by READ/DATA or by using LET statements twice.

Note: Please consult the machine manual for DEFFN statement before running the programs in the

machine.

27.4.2 Defining a subroutine -The GOSUB and RETURN statements

A subroutine is a collection of statements belonging to a process, which requires to be repeated very

frequently in the program. A subroutine consists of set of program statements that may be used

repeatedly at different places throughout the main program. In the main program the subroutines are

called at different places using GOSUB statement.

GOSUB Statement

Syntax: line number GOSUB n

Where n is the line number of the 1st statement in the subroutine.

Subroutines are placed at the end of the main programs in order to repeat a process. The program

control has to exit from the main program to enter a subroutine and after the process is completed it

comes back to the main program using RETURN statement.

RETURN statement

Syntax: line number RETURN

The RETURN statement in the subroutine transfers the control back to the main program to the line

immediately following the corresponding GOSUB statement. RETURN is the last statement in the

subroutine.

GOSUB and RETURN are always used together in the program not independently.

Properties of GOSUB

One subroutine can follow another subroutine but each subroutine should be complete within

itself.

GOSUB unconditionally transfers the program from the main to the subroutine.

GOSUB can also transfer the program conditionally by using it with IF-THEN ELSE

Syntax: Line number IF (Logical expression) THEN COSUB (line number) ELSE GOSUB (line

number)

98

A subroutine can be called by the main program a number of times. But the returning point will

be different in each time.

GOSUB takes the control from the main program to the subroutine and return brings back the

control from the subroutine to the main program.

Problem 1

Write a program to add, subtract, multiply and divide any two numbers.

10 INPUT A, B

20 INPUT "CHOICE", C$

30 IF C$ = "ADD" THEN GOSUB 80 : GOTO 65

40 IF C$ = "SUB" THEN GOSUB 120 : GOTO 65

50 IF C$ = "MUL" THEN GOSUB 170 : GOTO 65

60 IF C$ = "DIV" THEN GOSUB 210

65 PRINT C

70 END

80 REM "SUBROUTINE FOR ADDITION"

90 LET C = A + B

91 RETURN

120 REM "SUBROUTINE FOR SUBTRACTION"

130 LET C =A-B

150 RETURN

170 REM "SUBROUTINE FOR MULTIPLICATION"

180 LET C = A*B

200 RETURN

210 REM "SUBROUTINE FOR DIVISION"

220 LET C = A/B

240 RETURN

Short form of Problem 1 for addition

10 INPUT A, B

20 INPUT "CHOICE" C$

30 IF C$ = "ADD" THEN GOSUB 50

40 END

50 PRINT A+B

60 RETURN

99

So whatever will be the input of C$ in line number 20, GOSUB will go to these subroutines as it is

written for C$ = "ADD" similar subroutines will follow for "SUB", "MUL", "DIV" ON GOSUB

statement is similar to ON GOTO.

Syntax is given as:

Line no ON Numeric variable GOSUB

Or

Numeric expression

(Line number of sub-routine

1, sub. 2, sub .3….)

Program 2

10 INPUT A,B

20 INPUT "1-ADD, 2-SUB, 3-MUL, 4-DIV"; N

30 ON N GOSUB 50, 60, 70, 80

40 END (To make the program repeat we should add GOTO 10)

50 PRINT A+B : RETURN

60 PRINT A-B : RETURN

70 PRINT A*B : RETURN

80 PRINT A/B : RETURN

Note: To make the program repeat, we should add GOTO 10 at line 35

IN-TEXT QUESTIONS 3

1. (a) What is a subscripted variable?

(b) What is the function of a DIM statement?

(c) Define a subroutine?

(d) What does a RETURN statement do?

2. What is displayed when each of the following program segments is run?

(a) 10 GOSUB 400

20 GOSUB 500

100

30 PRINT "ONE"

40 END

400 PRINT "TWO"

410 RETURN

500 PRINT "THREE"

510 RETURN

(b) 10 DEF FNA (W) = 2*W+1

20 PRINT FNA (2)

30 LET x = 3

40 PRINT SQR (FNA (x+1))

50 END

27.5 EXAMPLES AND PROGRAMS SHOWING USAGE OF SOME BASIC FUNCTIONS:

INT, MOD, RND, LOCATE, LEN, VAL, STR$, RIGHT$, MID$

27.5.1 INT Functions

It takes a numeric value as its argument and returns its value after truncating the decimal part. The

value returned is always smaller than the number provided as the argument. For example,

10 Y= INT(13.2)

20 X= 15.6

30 Y= INT(X)

Statement 10 will return Y = 13 and

Statement 30 will return Y = 15.

Example 1

Two numbers A and B are given. To find the higher number between them:

Program 1

10 INPUT "HIGHER NO"; A

20 INPUT "SMALLER NO ";B

30 LET C = A/B

40 IF INT(C)= C THEN PRINT “ HIGHER NUMBER=“; A

50 END

This shows the use of the INT function.

101

Example 2

Write a program to find whether any year of the current century is a leap year or not.

Program 2

10 REM ** PROGRAM TO FIND WHETHER THE YEAR IS A LEAP YEAR OR

15 REM NOT **

20 PRINT "ENTER THE YEAR"

30 PRINT

50 INPUT YEAR

60 LET Y1 =INT(YEAR/4)

70 LET Y2 =YEAR/4

80 IF Y1 =Y2 THEN 110

90 PRINT YEAR "IS NOT A LEAP YEAR"

100 GO TO 120

110 PRINT YEAR; "IS A LEAP YEAR"

120 END

(A) Suppose we input year as 1988, then line number 60, we compute Y1 as 497 and also line number

70 gives Y2 as 497. Thus line number 80 gives Y1=Y2 and so the control is transferred to 110.

(B) Suppose we input year as 1989. The line number 60, we compute Y1 as 497. In line number

70, we get Y2 as 497.25. Thus in line number 80 Y1 is not equal to Y2, therefore control passes to 90.

27.5.2 MOD FUNCTION

Program 3

10 INPUT C, D

20 LET X= C MOD D

30 PRINT X

40 END

The MOD function determines the remainder on dividing a number by another. For example, 9 MOD

2 will give 1.

27.5.3 THE RND, LOCATE function

RND generates random numbers between 0 and 1.

Program 4

102

10 LET C= INT (RND*80)+1

20 LET R= INT( RND*25)+1

30 LOCATE R, C : PRINT "*"

40 GO TO 10

50 END

RND*80 and RND*25 generates random numbers between 0 to80 and 0 to25 respectively. Thus, in

line number 10,20 C is assigned the integer value of RND*80 plus 1 and R is assigned the value

RND*25 plus I respectively. The LOCATE clause followed by R,C followed by PRINT "*", prints a

"*'in the Rth row an Cth column.

27.5.4 THE LEN, VAL, STR$ function

LEN is used to count the number of character in a string. It takes a string as an argument and counts

every character including a blank.

Example

10 LET C$ = "BEAUTIFUL"

20 LET C = LEN (C$)

30 PRINT C

40 END

Output is 9 (as there are 9 characters in the word BEAUTIFUL. Note that the function LEN returns a

numeric constant.

VAL(X$) function returns a numeric constant equivalent to the value of the number represented by

the string X$. This string X$ should consist of all digits.

Example

10 LET X$= "12345"

20 LET Y = VAL(X$)

30 PRINT Y

40 END

Output of this program, on execution, will be 12345.

STR$(Y)

This is the reverse operation of VAL. The value of Y here is converted into a string literal. Y can be a

numeric constant, variable or expression.

Example

103

10 LET Y =7384

20 LET X$=STR$(Y)

30 PRINT X$

40 END

The output will be “7384”. The numeric value of Y is converted to string in line number 20, i.e. X$ =

“7384”

27.5.5 String Processing in BASIC

Following are the few functions, which operate on string variables and help in string processing.

Left String

LEFT$ (X$,Y) Returns the left most Y characters from the string X$

Example 1

10 LET X$ = "MATHEMATICS"

20 PRINT LEFT$ (X$, 4)

30 END

The output will be MATH

Example 2

10 LET C$ ="INFORMATICS"

20 LET D$ = LEFTS(C$,6)

30 PRINT D$

40 END

Output will be INFORM.

Right string

RIGHT$(Y$,X) returns the rightmost X characters from the string Y$

Example 3

10 LET X$ = "PORTBLANK"

20 PRINT RIGHT$(X$,5)

30 END

Output will be BLANK.

Example 4

10 LET A$ = "MANAGED"

20 LET B$ = RIGHT$ (A$,4)

104

30 PRINT B$

40 END

Output will be AGED.

Middle String

MID$(X$,X,Y) Returns a sub string of X$ starting at the character position X from the left and

containing Y characters.

Example 5

10 LET X$ = "MANHATTAN"

20 PRINT MID$(X$,4,3)

30 END

Output will be HAT.

IN-TEXT QUESTIONS 4

1. (a) What is the use of an INT function?

(b) What would be the value of X in the following program segments?

(i) C$ = "AVAILABLE"

X = LEN(C$)

(ii) C$ = "899"

X = VAL(C$)

2. If A$ = "TO ERR IS HUMAN" B$ = "TO FORGIVE DIVINE", find the values of following

functions:

(a) LEFT$(A$,2)

(b) MID$(A$, 2, 3)

(c) RIGHT$ (B$, 4)

(d) A$ +" " +B$

(e) MID$ (A$,4, 3) + MID$ (B$,5,2)

27.6 EXAMPLE PROGRAMS

Problem 1

Write a program to invert TAERG to GREAT.

105

Program 1

5 LET L$ = “ ”

10 LET C$ = "TAERG"

15 L = LEN(C$)

20 FOR X = L TO 1 STEP -1

30 LET L$ = L$ +MID$(C$,X,1)

40 NEXT X

50 PRINT L$

60 END

Output GREAT

Problem 2

Write a program to give the word GRAPEFRUIT and FRUITGRAPE when GRAPE and are

separately. Given

Program 2

10 LET F$ = "GRAPE"

20 LET B$ = "FRUIT"

30 LET C$ = F$ +B$

40 PRINT C$

50 LET A$ = B$ +F$

60 PRINT A$

70 END

Line 40 prints GRAPEFRUIT

Line 60 prints FRUITGRAPE

Problem 3

The prices of different articles are stored in a one-dimensional table, there product code is also given

as:

Price in Rs. 20 15 16 18 14

Product Code 1 2 3 4 5

106

Let us assume that product code and quantity sold for an article is inputted through keyboard. Write a

program to calculate and print the cost of sale along with product code and quantity sold. Terminate

the procedure when the product code is out of range.

Program 3

10 DIM P (5)

20 FOR C = 1 TO 5

30 READ P(C)

40 NEXT C

50 DATA 20,15,16,18,14

60 INPUT "PRODUCT CODE"; C

70 IF C<1 OR C>5 THEN END

80 INPUT "QUANTITY SOLD"; Q

90 LET S = Q*P(C)

100 PRINT "PRODUCT CODE"; C ; "QUANTITY SOLD "; Q; COST OF SALE" ; S

110 GO TO 60

Line number 70 contains END.

Problem 4

A set of given numbers are there. Write a program to arrange them in descending order.

Program 4

10 REM PROGRAM TO ARRANGE THE GIVEN NUMBERS IN DESCENDING

ORDER

15 DIM X (25)

20 INPUT "HOW MANY NUMBERS ARE THERE",N

50 FOR I = 1 TO N

60 READ X (I)

65 NEXT I

70 PRINT "ORIGINAL ORDER IS:"

80 FOR I = 1 TO N

90 PRINT X(I) ;

100 NEXT I

110 PRINT "NUMBERS IN DECREASING ORDER"

120 FOR I = 1 TO N-1

130 FOR J= 1 TO N-1

140 IF A (J)>=A (J+1) THEN 180

107

150 TEMP= A (J)

160 A (J)= A (J+1)

170 A (J+1) =TEMP

180 NEXT J

190 NEXT I

200 FOR I = 1 TO N

210 PRINT A (I);

220 NEXT I

230 END

Problem 5

From the word "MAIDAMS" write the message "MADAM IS MAD"

Program 5

10 LET A$ = "MAIDAMS'

20 PRINT LEFT$(A$, 2)+MID$(A$,4,3); MID$(A$,3,1)+

RIGHT$(A$, 1);LEFT$(A$,2)+MID$(A$,4,1)

30 END

Line number 20 can be put in two consecutive PRINT statement also.

Problem 6

Write a program to print the Prime Numbers between any two numbers A (say 1) and B (say 100).

Program 6

10 INPUT “TWO NUMBERS”; A,B

20 FOR N= A TO B STEP 1

30 IF N MOD 2= 0 OR N<= 1 THEN GO TO 80

40 FOR X=3 TO SQR(N) STEP 2

50 IF N MOD X =0 THEN 80

60 NEXT X

70 PRINT N; “IS THE PRIME NO”

80 NEXT N

90 END

Explanation

In the line number 30, N MOD 2 is same as MOD(N,2) it gives the remainder of N/2, similarly in line

number 50,N MOD X means remainder of N/X.

108


In this lesson we have discussed various statements relating to decision making, looping and

branching. Use of subroutine, sub-programs and arrays has been explained clearly by taking number

of examples. These commands play very important role in writing programs. The illustrations given in

this lesson will help you for a better grasp of BASIC programming. Usage of some BASIC functions

has been clearly defined for the benefit of the students.


1. Write a BASIC program to run up the following series

(a) 1,3,5,7, 9 ………………100

(b) 2,4,6,8,10………………100

(c) 1,4,9,16,25………………100

(d) 1,8,27,64,125……………1000

2. What will be the output of the following programs?

(a) 10 FOR I = 1 TO 3

20 FOR J = 1 TO 5

30 PRINT I, J, I+J

40 IF J = 3 THEN 100

50 PRINT I, J , I*J

60 PRINT I+J, I-J

70 PRINT

100 NEXT J

110 NEXT I

120 END

(b) 10 FOR I = 1 TO 5

20 READ K

30 PRINT I ;

40 FOR J = 1 TO K

50 PRINT ““;

60 NEXT J

70 PRINT

80 NEXT I

90 DATA 5,9,3,2,6

100 END

3. Write a program to invert LOOHCS to SCHOOL.

109

4. Write a program to write

PANKAJ KUMAR GOEL as P.K. GOEL.

5. Write a program to write your own address 10 times on the screen.


IN-TEXT QUESTIONS 1

1. (a) S

(b) I

(c) Positive odd

2. (a) 40 NEXT J

50 NEXT K

(b ) 50 NEXT I

3. (a) 7 9 11

(b) 2

3

4

5

7

8

9

10

11

IN-TEXT QUESTIONS 2

1. (a) True

(b) True

(c) False

2. (a) FAX(1,3,) = 15, FAX(2,1) = 25

(b) FAX(2,2) = 30, FAX(1,4) = 20

3. 4 4 5

4. 10 LET SMALL = X(1,1)

110

20 LET LARGE = X(1,1)

30 FOR I = 1 TO 4

40 FOR J = 1 TO 5

50 IF X(I,J) < SMALL THEN LET SMALL = X(I,J)

60 IF X(I,J) > LARGE THEN LET LARGE = X(I,J)

70 NEXT J

80 NEXT I

90 PRINT "SMALLEST VALUE ="; SMALL

100 PRINT "LARGEST VALUE ="; LARGE

110 END

5 10 DIM A(5)

20 REM READ NUMBER OF DATA VALUE

30 READ N

40 REM READ DATA VALUE INTO ARRAY A

50 FOR I =1 TO N

60 READ A(I)

70 NEXT I

80 REM NOW SORTING STARTS

90 FOR M = 1 TO N-1

120 IF A (M+1) > = A(M) THEN 18 0

130 REM INTERCHANGE OF DATA VALUES

140 LET P = A(M)

150 LET A (M) = A (M+1)

160 LET A(M+1) = P

180 NEXT M

190 REM PRINT THE SORTED ARRAY

200 FOR K = 1 TO N

210 PRINT A (K);

220 NEXT K

230 DATA 5, -71, -20, 14, 0, 5

240 END

IN-TEXT QUESTIONS 3

1. (a) A list of quantities can be given one variable name using a subscript. Such

a variable is called a subscripted variable.

(b) It defines the number of memory locations required for the array name.

111

(c) It is a collection of statements, which requires to be repeated very frequently

in a program. It is placed at the end of the program and may be referred to at

different places in the main program using GOSUB statement.

(d) RETURN transfers the control back to the main program, to the statement

immediately following the subroutine call.(i.e. GOSUB statement)

2. (a) TWO

THREE

ONE

(b) 5

3

IN-TEXT QUESTIONS 4

1 (a) It takes numeric value as its argument and returns its value after truncating its

decimal part.

(b) (i) 9

(ii) 899 (As numeric value)

2 (a) TO

(b) O E

(c) TO ERR IS HUMAN TO FORGIVE DIVINE

(e) ERROR

LESSON 28

PROCESSING FILES IN BASIC

28.1 INTRODUCTION

We have so far discussed programs where data is supplied either through READ...DATA statements

or through INPUT statements. But it is difficult to handle large volume of data with the help of these

statements. Moreover, data stored in one program cannot be shared by other programs. The above

limitations can be overcome by placing the data into a separate storage area called a data file.

A date file forms an essential framework of a data processing system. It is a collection of data

organised in a specific format and for a specific purpose, which is kept somewhere in external

memory. A file can be described as a collection of records where a record consists of number of data

values, which are either produced by a computer as per the instructions of a program or given to the

112

computer as a data. A typical data processing system many consist of many files. Many records in a

file contain detailed information about some aspect of the system. For example, a "pay file" may

contain one record for each employee containing all the particulars such as Employee Code, Name,

Address, Basic pay, HRA, DA, CCA, Designation, Sex, etc. Each partition is a data item and is

referred to as a field. A number of BASIC Programs can use this file as input.

File handling methods differ widely from system to system. In this lesson, we will discuss the

methods that are currently used in most of the IBM compatible systems.

28.2 OBJECTIVES

On completion of this lesson, you should be able to:

understand various types of files

know how to handle sequential files

know how to handle random access files

discuss various examples/ programs relating to these two type of files.

28.3 TYPES OF FILES

Depending on the way in which the data is stored and accessed, files are categorised as:

Sequential access files

Direct (Random) access files

Sequential Access Files

These files may be created on a magnetic tape or disk. Data from these files is read sequentially, item

after item, starting at the beginning. Though sequential access file is easy to handle, yet it has a

serious disadvantage. In the sequential file we cannot change the existing entry or insert a new entry.

To do this, we should copy the entire content to another file making the changes on the way and then

copy the correct data back in to the original file. Another disadvantage is that we cannot simply locate

or go back to read a particular data item.

Fig. 28.1 and 28.2 show how data is stored on magnetic tapes and disk respectively. A disk consists

of a number of concentric circles known as tracks. The data items are stored on these tracks

sequentially.

113

Fig. 28.1 Sequential File on a Tape

Consider an inventory file shown in Table 28.1

Part name Part number Price Quantity

AAAA 101 8.00 100

BBBB 102 10.00 200

CCCC 103 12.00 300

Table 28.1 Inventory file

114

Fig. 28.2 Sequential File on a Disk

Details of each part are stored in one record. When we complete all the parts, the data file would look

like a long column of values as shown below:

AAAA

101

8.00

100

BBBB

102

10.00

200

CCCC

103

12.00

300

Programs are written to read these data values one after another.

Random Access Files

Random access files are created on disks to allow us to read or write from the files in random order.

Random access files allow more flexible access than the sequential files. You can read or write any

record directly in a random file without searching through all the records that precede it. Thus,

reading and writing of data is faster.

28.4 HANDLING OF SEQUENTIAL FILES

Using data files would require the incorporation of statements in your program to perform the

following functions:

Giving a name to the file

Opening the file

Writing to or reading from the file

Closing the file

115

28.4.1 Naming a file

A file is identified by its file specifications. It is of the form:

Device name: File name

The device name tells the system which device to look for the file and the file name tells which file to

look for on that device. The device name should be followed by a colon as indicated. Examples are:

A: MEAN

B: STUDENT. MKS

The device names A and B indicate the disk drive one and two respectively

File names can have a maximum of eight characters. However, the files stored on disks may have a

file name extension in the following form.

NAME.EXT

The extension consists of a period and followed by three letters. When you use longer file name, one

of the following conditions may occur.

File Name Result

1. Extension is longer than three characters. Extra characters are truncated.

2. Name is longer than eight characters. A period is inserted after the eighth character and

extra characters (up to three) are used as the

extension.

3. Name is longer than eight characters and

extension is included.

Gives an error.

For example,

SURENDERKUMAR becomes SURENDER.KUM.

PROGRAM.PENSION becomes PROGRAM.PEN.

PAYROLLCALUCTION.BAS gives an error.

28.4.2 Opening a file

It is necessary to establish a line of communication between a program and a file that is to be used

before data can be read from or written to that file. This is achieved by using the OPEN command as

shown below:

OPEN ["Mode", #file number, "file name"]

Mode is a string constant and takes one of the following three forms

O for sequential output file

116

I for sequential input file

R for random input/output file

It should be noted that the mode is enclosed in quotation marks.

File number is an integer number and can be any number between 1 and 15. It is a unique number

associated with the actual physical file. A file number may be a number, variable, or expression.

File name specifies the particular file to be used. This should conform to the specifications of the file

when it was created. File names must be enclosed in quotations.

Examples of opening sequential files for input and output operations are:

10 OPEN "I" # 1, " PANKAJ.DTA"

20 OPEN "O", # 3, "TEMP"

These can also be written as

10 OPEN" PANKAJ.DTA" FOR INPUT AS# 1

20 OPEN" TEMP" FOR OUTPUT AS #3

If a file opened for input operation does not exist, a "FILE NOT FOUND" error will be shown on the

screen. If a file, which does not exist, is opened, in that case file will be created. It is important to note

that opening a file for output destroys the existing data in that file.

28.4.3 Closing a File

A previously opened file can be closed using the CLOSE statement as follows

CLOSE [# file number, #file number, ......]

The file number is the number used in the OPEN statement. For example, the statement.

100 CLOSE #1, # 3

causes the files with file numbers 1 and 3 to be closed. The CLOSE statement is used when you have

finished processing data from a file.

A CLOSE statement with no file numbers specified causes all files that have been opened to be

closed.

You should also note that execution of END and RUN statements also causes all open sequential files

to be automatically closed. However, STOP does not close any files.

28.4.4 Writing Data to a File

We may write data to a sequential file using either of the following two statements.

117

PRINT [# file number, list of variables]

WRITE [ #file number, list of variables ]

File number refers to the file designator used when the file was opened for output. List of variables

specifies the data that is to be written to the file.

The difference between PRINT # and WRITE # Statements is that WRITE # inserts commas between

the data items and quotation marks for strings while PRINT # causes data to be written without any

delimiters (commas, etc.). For example consider the statement

40 PRINT #1 N $, AMT

In case N $ = " PANKAJ" and AMT = 2000, the

statement would write the following image to the file 1:

PANKAJ 2000

The statement

40 WRITE # 1, N $, AMT

would write the following image to the file 1:

"PANKAJ", 2000

The delimiters are useful when we try to read the data with an INPUT # statement.

Let us take an example for proper understanding the use of "WRITE" and "PRINT" statement.

Example 1

Program

10 REM *** PROGRAM INVENTI ***

20 REM -- PNM$ PART NAME

30 REM -- PN PART NUMBER

40 REM -- P PRICE

50 REM -- QTY QUANTITY

60 OPEN "O", # 1, "INVENT. DTA"

70 FOR I =1 TO 3

80 INPUT "NAME" ; PNM$

90 INPUT "NUMBER" PN

100 INPUT "PRICE" P

110 INPUT "QUANTITY" ; QTY

120 WRITE # 1, PNM$, PN, P, QTY

130 PRINT

140 NEXT I

150 CLOSE #1

118

160 END

Output

NAME? AAAA

NUMBER? 101

PRICE? 8

QUANTITY? 100

NAME? BBBB

NUMBER? 102

PRICE? 10

QUANTITY? 200

NAME? CCCC

NUMBER? 103

PRICE? 12

QUANTITY? 300

28.4.5 Reading Data from a File

Data can be read from a sequential file using the INPUT # statement. It takes the form

INPUT [ # file number, list of variables ]

The following INPUT # statement can be used to read data from the file INVENT. DTA:

200 INPUT #1, PNM$, PN, P, QTY

The type of data in the file must match the type specified in the list. Unlike INPUT, no question mark

is displayed with INPUT #

The following example will illustrate clearly the use of INPUT # statement.

Example 2

Write a program to read inventory data stored in the file INVENT . DTA inventory and print the table

with the value of each product.

Program

10 REM ** PROGRAM INVENT 2 **

20 OPEN I",#1, "INVENT. DTA"

119

25 PRINT "PART", "PART", " PRICE", "QUANTITY", " VALUE "

30 PRINT "NAME","NUMBER"

40 PRINT

50 INPUT #1 PNM$, PN, P, QTY

60 LET V= P* QTY

70 PRINT PNM$, PN, P, QTY, V

80 GOTO 50

90 CLOSE

100 END

Output

PART PART PRICE QUANTITY VALUE

NAME NUMBER

AAAA 101 8 100 800

BBBB 102 10 200 2000

CCCC 103 12 300 3600

Input past end in 50

The program in Example 2 reads sequentially, every item in the file. When all the data have been

read, line 50 causes an "Input past end" error. This can be avoided by using the EOF function. This

function tests for end of file and the control is directed appropriately. The end of the file is indicated

by a special character in the file.

The program INVENT2 is modified as follows:

10 REM ** PROGRAM INVENT 2**

20 OPEN "I", #1 "INVENT. DTA"

25 PRINT "PART", "PART","PRICE, "QUANTITY" "VALUE"

30 PRINT "NAME", "NUMBER"

40 PRINT

50 IF EOF (1) THEN 100


70 LET V = P*QTY

80 PRINT PNM$, PN, P, QTY, V

90 GOTO 50

100 CLOSE

110 END

120

28.4.6 Reading lines from a File

The LINE INPUT # statement may be used to read an entire line, ignoring delimiters, from a

sequential file and assign to a string variable. It is of the form

LINE INPUT [ #file number, string variable ]

File number is the number under which the file was opened and string variable is used to store a line

of string constant.

LINE INPUT # reads all characters in the sequential file up to a carriage return which was inserted by

the PRINT # statement. The next LINE INPUT # reads all characters up to the next carriage return.

Example 3 illustrates the use of LINE INPUT #statement.

Example 3

Write a program to input employee addresses from the keyboard, store them in a file named

ADDRESS, and read back to produce a list.

Program

10 REM ** PROGRAM EMPLOYEE **

20 REM ** INPUT EMPLOYEE ADDRESS THROUGH KEYBOARD **

30 OPEN "O ", #1 "ADDRESS"

40 FOR I = 1TO 3

50 LINE INPUT "TYPE IN ADDRESS" ADDR$

60 PRINT # 1 ADDR$

70 NEXT I

80 CLOSE 1

85 PRINT

90 OPEN : "I" # 1, "ADDRRESS"

100 FOR I= 1 TO 3

110 LINE INPUT # 1, ADDR$

120 PRINT ADDR$

130 NEXT I

140 CLOSE 1

150 END

Output

121

TYPE IN ADDRESSES? PANKAJ KUMAR GOEL, PITAMPURA, DELHI -34

TYPE IN ADDRESSES? RAJESH KUMAR, AUDIT OFFICE, GWALIOR

TYPE IN ADDRESSES? DR. SANJU, MEDICAL COLLEGE, JODHPUR

PANKAJ KUMAR GOEL, PITAMPURA, DELHI-34

RAJESH KUMAR, AUDIT OFFICE, GWALIOR

DR. SANJU, MEDICAL COLLEGE, JODHPUR

28.4.7 Adding Data to a Sequential File

To add any data to a sequential file that is already residing on a disk, you cannot just open the file and

write data to it. You must note that when a sequential file is opened for output, its current contents

are lost. In such cases, you should open the file with APPEND. For example, the statements

10 FILE = " A: TEMP"

20 OPEN FILE FOR APPEND AS #1

will open the file named TEMP on the disk in drive A and position the file pointers at the existing

data. Now we can add records to the file, which has been numbered as 1.

Following example will illustrate the use a of Append

Example 4

Write a program to add two more products to the file "INVENT. DTA" created earlier in Example 1.

DDDD 104 20.0 200

EEEE 105 30.0 300

Program

10 FILES = "INVENT. DTA"

20 OPEN FILES FOR APPEND AS #1

30 FOR I=1 TO 2

40 INPUT PNM$, PN, P, QTY

50 WRITE #1, PNM$, PN, P, QTY

60 NEXT I

70 CLOSE # 1

80 REM ** DATA INPUT FROM FILES **

90 OPEN "I", #1, "INVENT. DTA

100 PRINT

110 IF EOF (1) THEN 160


130 PRINT PNM$, PN, P, QTY

122

140 GOTO 110

150 CLOSE # 1

160 END

Output

? DDDD, 104, 20, 200

? EEEE, 105, 30, 300

AAAA 101 8 100

BBBB 102 10 200

CCCC 103 12 300

DDDD 104 20 200

EEEE 105 30 300

28.5 HANDLING OF RANDOM ACCESS FILES

Unlike sequential files, random files cannot be created so easily. Random files require more

programming steps and skills. However, since random access files effectively retrieve or write

individual data items anywhere in the file they are often preferred.

28.5.1 Creating a Random File

Following are the steps required to create a random file:

Open the file

Allocate space in the random buffer for variables that will be written to the file

Move the data into the random buffer

Write the data from the buffer to the disk

Step1: Like sequential files, we may open random files using the OPEN Statement

.

OPEN ["R", #File number,"File name",Record length]

The character R indicates that the file to be opened is a random access file. Record length is a number

that specifies the length of records. The length may range from 1 to 32767, The default record length

is 128 bytes. For examples,

100 OPEN "R", #2, "PANKAJ',100

200 OPEN "R",#3, "CHAP5",120

These statements can also be written as

123

100 OPEN "PANKAJ" AS#2LEN =100

200 OPEN "CHAPS," AS #3 LEN = 120

Step2: Space in the random buffer is allocated by the FIELD statement in the form

FIELD [#file number, w1 AS u1, w2 AS u2...]

File number is the number of the concerned file just opened, w1 specifies the number of character

positions to be allocated to the string variable and so on.

A FIELD statement defines variables that are used to put data into or get data out of a random buffer.

For example, the statement

50 FIELD #2, 20 AS A$ 10 AS B$

defines two string variables A$ and B$ and allocates first 20 bytes to the variable A$ and next bytes to

B$. Note that FIELD is a declaration statement and does not actually place data into the random

buffer.

Unlike sequential files, random files cannot be created so easily. Random files require more

programming steps and skills. However, since random access files effectively retrieve or write

individual data items anywhere in the life, they are often preferred.

The total number of bytes allocated in a FIELD statement must not exceed the record length specified

in the OPEN statement. For instance, the statements

10 OPEN "R",#2 "CHAP1",40

20 FIELD #2,20 AS A$, 5 AS B$, 10 AS C$, 10 AS D$

open a file named CHAP1 as a random file and allocates character positions as follows:

First 20 bytes to A$

Next 5 bytes to B$

Next 10 bytes to C$

Next 10 bytes to D$

Note that the total number of bytes allocated is 45, which is more than 40, the record length as defined

in the OPEN statement in line 10. In this case, a "Field overflow" error will appear on the screen.

Step 3: Placing data into the random file buffer is done by the LSET and RSET statements. They take

the form:

LSET u$ = x $

RSET u$ = x $

124

Where u$ is the name of a string variable that is defined in a FIELD statement and x$ is a string

variable representing the data to be placed into the field identified by u$ Examples of these statements

are:

30 LSET A$ = F1$

40 RSET B$ = F2$

LSET statement left-justifies the string in the field, and RSET statement right justifies the string. Let

us suppose F1$ represents CONNECTING-PROD and F2$ represents 5000. If the character positions

allocated to A$ is 18 andB$ is 5, then the field represented by A$ and B$ in the random buffer are

filled like this:

C O N N E C T I N G - P R O D 5 0 0 0

|--------------------------------------A$------------------------------------------|---------------|

Since all the fields in a random buffer are defined as string fields, any number value that is to be

placed in a random file buffer must be converted to string value before it is LSET or RSET. This can

be done using the following `convert' functions.

MKI$ converts an integer to a 2-byte string.

MKS$ converts a single-precision number to a 4-byte string.

MKD$ converts a double-precision number to an 8-byte string.

LSET A$ MKI$ ( integer variable)

or

RSET A$ MKD$ (double-precision variable)

Where A$ is the string variable defined in the FIELD statement.

For example LSET A$ - MKI$(RN)

RSET B$- MKS$ (PAY)

Step 4: Moving of data from a random buffer to a random file is done by the PUT statement.

Each time a PUT statement is executed, a record is written to the file.

PUT {# file number, record number]

125

File number refers to the number under which the file was opened. Record number is the number of

the record to be written and expressed as an integer constant or variable. If record number is omitted,

the record will have the next available number. For example, the statement

100 PUT #2, 1

will write the information contained in the buffer to the first record of the random file numbered 2. It

can also be written as

100 PUT #2,K

where K is an integer variable. The value of K must be defined before using the PUT statement.

Each time a PUT statement is executed, a record is written to the file.

Let us take an example to clarify various statements discussed for creating a random file.

Example 5

Write a program to open a random and record salary file statement of employees with the following

details:

1 Name

2 Basic Pay

3 D.A.

4 H.R.A.

5 C.C.A.

Assume the following data:

Name Basic Pay D.A. H.R.A. C.C.A.

UPMA 25,000 5000 8000 2000

SANJU 20,000 4000 7000 1500

ANAMIKA 15,000 3000 6000 1000

Program

10 REM ** CREATION OF RANDOM FILE **

20 OPEN " R",#1,"SALARY" 60

30 FIELD #1,20 AS N$, 10 AS B$ 10 AS D$, 10 AS H$, 10 AS C$

40 INPUT "RECORD NUMBER"; I

50 IF I=0 THEN 150

60 INPUT "NAME "; A$

70 INPUT "BASIC PAY"; P

80 INPUT " DEARNESS ALLOWANCE"; Q

82 INPUT "HOUSE RENT ALLOWANCE"; R

126

85 INPUT " COMPENSATORY CITY ALLOWANCE"; S

100 LSET N$ = A$

110 LSET B$ = MKS$ (P)

120 LSET D$ = MKS$ (Q)

122 LSET H$= MKS$ (R)

125 LSET C$ = MKS$ (S)

130 PUT # 1, I

140 GOTO 40

150 CLOSE # 1

160 END

Output

Record Number? 1

Name? UPMA

Basic pay? 25000

Dearness Allowance? 5000

House Rent Allowance? 8000

Compensatory city Allowance ? 2000

Record Number? 10

Name? SANJU

Basic pay? 20000

DA? 4000

HRA 7000

CCA? 1500

RECORD NUMBER? 40

Name? Anamika

Basic Day? 15000

DA? 3000

HRA? 6000

CCA? 1000

Record Number 0

28.5.2 Accessing a Random File

Like creation, accessing a random file includes the following points:

Open the file for random access

127

Allocate space in the random buffer for variable using the FIELD statement that will be read from

the file.(Remember that if a program performs both the input and output on the same random file,

you may use only one OPEN statement and one FIELD statement)

Bringing data from the file to the buffer for processing

Access and use data in the program

Step 1: Follow the procedure of step 1 in creating a file. (see Section 5.4.1)

Step 2: Follow the procedure of step 2 in creating a file. (see section 5.4.1)

Step 3: Bringing data from the file to the buffer is done by the GET statement. This is similar to the

PUT statement.

GET [#file number, record, number]

Record number is optional and, if it is omitted, the next record (after the last GET ) is read into the

buffer. For example,

200 GET #2, 10

will transfer the content of the record number 10 from the file number 2 to the buffer.

Step 4: After a GET statement, the data available in the buffer can be used by the program for further

manipulation and printing outputs. Remember that the numeric values are recorded as string values in

the buffer and therefore all numeric values must be converted back to numbers for performing any

arithmetic operations on them: This is done using following "convert" functions:

CVI converts a two-byte string to an integer.

CVS converts a 4-byte string to a single-precision number.

CVD converrts an 8-byte string to a double-precision number.

These functions are written in the form:

x = CVI (u$)

x = CVS (u$)

x = CVD (u$)

u$ is the name of a string variable containing numeric values in the buffer and x is a numeric variable

representing the data to be used in the program.

The following program segment illustrates the use of GET and convert functions:

40 FIELD #2, 10 AS A$, 6 AS B$, 3 AS C$

50 GET #2

55 LET N$ = A$

128

60 LET M1 = CVS (B$)

70 LET R1 = CVI (C$)

80 PRINT N$, M1, R1

This program uses a random file numbered 2, which has fields as defined in line 40. Line 50 reads a

record from the file. Line 60 converts the contents of to a single-precision numeric value and assigns

it to the variable MI. Similarly, line 70 converts the contents of to an integer number and assigns the

value to the variable R1. Line 80 writes the vales of N, MI and R1 on the screen.

In this case, N$, M1 and R1 may represent student names, marks and class rank. Note the conversion

functions do not change the actual data. They only change the way the data is interpreted.

Remember that B$ and C$ were originally numbers which would have been written to the file using

the MKS$ and MKI$ functions. Example 6 will help us in understanding the technique of accessing

data stored in random life.

Example 6

Write a program to access the random file "SALARY" that was created in example 5.

You are required to print the data contained in any desired record along with the total salary.

Program

10 REM ** ACCESSING A RANDOM FILE **

20 OPEN "R" # 1, " SALARY", 60

30 FIELD # 1, 20 AS N$, 10 AS B$, 10 AS D$, 10 AS H$, 10 AS C$

40 INPUT "RECORD NUMBER' K

50 IF K=0 THEN 130

60 GET # 1, K

70 LET P = CVS (B$)

75 LET Q =CVS (D$ )

80 LET R =CVS (H$)

85 LET S = CVS (C$)

90 LET T = P+Q+R+S

100 PRINT "Record" K, N$, .P, .Q, .R, .S, .T

110 PRINT

120 GOTO 40

130 CLOSE

140 END

129

Output

RECORD NUMBER? 40

RECORD 40 ANAMIKA 15000 3000 6000 1000 25000

RECORD NUMBER? 1

RECORD 1 UPMA 25000 5000 8000 2000 40000

RECORD NUMBER? 10

RECORD 10 SANJU 20000 4000 7000 1500 32500

RECORD NUMBER? 0

IN-TEXT QUESTIONS 1

1. Determine whether the following statement to true or false

(a) A file can store a program's output for future use

(b) A file cannot be used by more than one program.

(c) When a file is opened for INPUT, data can be written from the program to the file.

(d) If a sequential file is created and then read in the same program, it must be closed and reopened

between these operations.

2. Correct the syntax errors in each statement.

(a) 10 OPEN "FILE 1" AS # 2 FOR OUTPUT

(b) 20 WRITE # 2 A, B, C, D,

(c) 30 KILL FILE 2

3 Following program segment is supposed to create and display (on the screen) in file containing the

integers from 1 to 100, but it does not run properly. Correct the errors.

10 OPEN "FILE1" FOR INPUT AS # 1

20 FOR I = 1 TO 100

30 PRINT # 1, I

40 NEXT I

50 FOR I= 1 TO 100

60 INPUT # 1, I

130

70 PRINT # 2, I

80 NEXT I

90 CLOSE # 1

100 END

4. Write a program in BASIC to create a file called "STUDENT' containing the following data:

(a) Name of the student

(b) Roll Number

(c) Marks in LOTUS

(d) Marks in dBASE

(e) Marks in BASIC

5. Write a program to retrieve data from the "STUDENT' file created in question 4 above and copy

the same in a file named "STUDENT"1.


In this lesson, we have discussed about processing of both sequential and random files. Although,

now-a-days advance programming languages are used to process files, file handling through BASIC is

quite simple and useful. Even today, BASIC files are quite popular in business data processing. It is

hoped that the fundamentals and the examples presents in this lesson will be helpful in understanding

the various steps involved in file processing and also to develop your own programs.


IN-TEXT QUESTIONS 1

1. (a) True

(b) False

(c) False

(d) True

2 (a) 10 OPEN "FILE1" FOR OUTPUT AS # 2

(b) 20 WRITE # 2, A, B, C, D

(c) 30 KILL "FILE 2"

3. CHANGE: 10 OPEN "FILE1" FOR OUTPUT AS # 1

70 PRINT I

INSERT: 45 CLOSE # 1

47 OPEN "FILE1" FOR INPUT AS # 1

4. 10 REM PROGRAM TO CREATE " STUDEN" FILE

131

20 OPEN "STUDENT" FOR OUTPUT AS # 1

30 PRINT "NAME, ROLLNO, LOTUS-MARKS, DBASE-MARKS, BASIC- MARKS"

40 PRINT "Type AAA, 0,0,0,0 TO MAKE AN END"

50 INPUT N$, R, L, D, B

60 IF N = "AAA" THEN 90

70 WRITE # 1, N$, R, L, D, B

80 GO TO 50

90 CLOSE # A

100 END

5. 10 REM PROGRAM TO COPY "STUDENT" FILE

20 OPEN "STUDENT" FOR INPUT AS # 1

30 OPEN "STUDENT1 FOR OUTPUT AS # 2

40 IF EOF (1) THEN 80

50 INPUT # 1, N$, R, L, D, B

60 WRITE # 2, N$, R, L, D, B

70 GO TO 40

80 CLOSE # 1

90 CLOSE # 2

100 END


1. Find the syntax errors in the following statements:

10 OPEN "FILES" AS #5 FOR OUTPUT

20 PRINT #6 A; ","; B$; ";"; PAY

30 INPUT #2, A: B: C

40 OPEN #2 LEN = 128

50 FIELD #1, A$ AS 10

2. The following program segment is supposed to create and display a file of numbers. Correct the

errors in it.

10 OPEN "NUMFL" FOR INPUT AS #1

20 FOR I = 1 TO 10

30 READ N

40 PRINT #3, N

50 NEXT K

60 FOR K = 1 TO 10

70 WRITE #1, N

132

80 PRINT N

90 NEXT I

100 CLOSE #1

110 DATA 5, 7, 9, 10, 12, 15, 17, 19, 20, 22

120 END

3. Suppose that a file named COMPUTE.DTA exists with 20 records of the form:

NM$ COST$

Correct the following program so that it displays the fifth record in this file on the screen:

10 OPEN "COMPUTER.DTA" A$ #1 LEN = 24

20 FIELD #1, 4 AS COST $, 20 AS NM$

30 GET #2, 5

40 LET NM$ = N$

50 LET COST$ = COST

60 PRINT #1, NM$, COST

4. Write a program segment that performs the following operations:

(a) Display the number of record of records in EMPLOYEE.DAT.

(b) Delete the fourth record from the file.

(c) Change the pay in the sixth record from Rs. 1500 to Rs. 2500.

5. Assume that a file PAYROLL exists with records with form Employee number (NUM), Name

(NM$), Rate of pay (RATE), and a sentinel record of 0, "AAA", 0. Write a program segment that

(a) Renames this file as PAY.

(b) Deletes a record with employee number 50.

(c) Adds the records 135, "SANJU", 12

(d) Change the rate of pay of employee number 140 from 15 to 20.

LESSON 20

INTRODUCTION TO DATABASE

20.1 INTRODUCTION

All of us are familiar with the term data. In fact, unknowingly we come across data in our day to day

life everyday. The age of a person, price of potato, number of students in a school, pin code of a city,

etc. are some examples of data. In our life we have to remember so much of data. But it is easier for

us to remember all information for a few individuals. For example, you may be in a position to tell

133

20 bytes 4 bytes

accurately the age, height, complexion, income, educational qualification, residential address, etc. of

your close friends. But it is too difficult for you to memorise all these information for a large number

of individuals. Let us consider the example of National Open School (NOS). Every year about one

lakh students take admission in NOS. If you are asked to memorise records of date of birth, subjects

offered and postal address of all these students, it will not be possible for you.

To deal with such problems we construct a database. We arrange all information about students in a

tabular form. We keep all the records so that if I am asked, ‘How many students are there in

Economics?’ I am in a position to answer.

20.2 OBJECTIVES

After going through this lesson you will be in a position to

explain the concept of database

appreciate the features of database management system (DBMS)

learn about the software packages available in the market to deal with database

Invoke the dBASE III + programmes

explain the advantages of dBASE III +

work in dBASE III +.

20.3 WHAT IS A DATABASE?

Let us begin with the concept ‘database’ and its management. Database is a collection of information

in a structured way. We can say that it is a collection of a group of facts. Your personal address book

is a database of names you like to keep track of, such as personal friends and members of your family.

Let us look into our earlier example of information on students in NOS. A sample of 5 students is

presented in the table below (see, Fig. 20.1). We have given 6 items of information on every student,

namely, Roll No, Name, Date of birth, Sex, Postal address and Subjects offered by the student.

Fig. 20.1 contains required details about each student. There are six pieces of information on each

student. They are Roll No, Name, Date of birth, Sex, Address and Subjects. Each piece of information

in database is called a Field. We can define field as the smallest unit in a database. Each field

represents one and only one characteristic of an event or item. Thus there are six fields in this

database.

ROLL NO NAME DATE OF

BIRTH

SEX ADDRESS SUBJECTS

134

9721001 Subrat Das 21.05.1980 M C36, Sector 2,

Bhubaneswar

Orissa

Pol Sc, Eco,

History, Eng,

Hindi

9721002 Aditya Bhoi 12.06.1981 M At/Po. Burla,

Sambal Pur

Phy, Chem,

Biology, Eng,

Hindi

9732012 Madhu Jain 03.01.1979 F A31, Pilani,

Rajasthan

Pol Sc, Eco,

History, Eng,

Hindi

9724004 Ahmad Ali 23.11.1979 M 12A, Sheikh

Sarai-I, New Delhi

Phy, Chem,

Biology, Eng,

Hindi

9715023 C. Suresh 07.09.1980 M 96, Malviya

Nagar, Bhopal

Pol Sc, Eco,

History, Eng,

Hindi

Fig. 20.1

If you take a close look at all these fields, they are not of the same type. Date of birth is date type

whereas Name is character type. In database there can be five categories of fields. They are:

Numeric

Character

Logic

Memo

Date

We will discuss about each type of field in detail later on in this lesson. First let us be familiar with

another concept that we will use frequently.

All the related fields for a particular event is called a Record. In the example above, all six fields

taken together for a particular student is called a record of that student. Hence, since there are six

students there are six records. Thus, we can define record as a collection of logically related fields.

Now we are in a position to define database in a formal manner. We can say that it is a collection of

logically related records. In other words a database is a collection of database files, and each database

file is a collection of records.

135

The task before us is creation of a database and its management. Data management involves creating,

modifying, deleting and adding data in files, and using this data to generate reports or answer queries.

The software that allows us to perform these functions easily is called a Data Base Management

System (DBMS). Using a DBMS files can be retrieved easily and effectively. There are many DBMS

packages available in the market. Some of them are:

dBASE III Plus

FoxBASE Plus

SoftBASE

Clipper

Paradox

There are some WINDOWS based database packages available in the market such as MS ACCESS

(part of MS OFFICE). In this lesson we will discuss about the package dBASE III + which is a DOS

based package. It provides many choices to work with the program. This means you can work through

both assist screen and dot prompt. It allows you to work with both financial figures and text.

20.4 HOW TO START dBASE III PLUS?

You can invoke dBASE III + either from Hard disk or from floppy drives. In these days more and

more people are using the Hard disk to run the program. The computer systems with two floppy

drives and no Hard disk are obsolete now. However, we will discuss the procedures to invoke dBASE

III + in both Hard disk and floppy drives systems.

Let us begin with the procedure of loading dBASE III + into systems with Hard disk. The steps that

you should follow are

1. Start the computer in the DOS mode. The C prompt will appear on the screen. It will look

like C:\>.

2. You have to change the directory to come into dBASE III +. Type CD\DBASE and press

ENTER key. You can type either lower case or upper case alphabets. The computer does

not distinguish between the two.

3. On the screen you will see C:\DBASE>.

4. Type DBASE and press ENTER key. The computer will take a few seconds to show the

copyright and logo of dBASE III + on the screen.

5. Press ENTER key again. The dBASE III + logo will disappear from the screen and main

menu of dBASE III Plus will appear. Now you are inside the dBASE III + program.

136

Now let us discuss how to load dBASE III + from floppy drives. Suppose your system does not have a

hard disk and there are two floppy drives. Note that dBASE III + comes in two diskettes: system disk

# 1 and system disk # 2. You have to obtain both the diskettes before loading the dBASE III + in your

computer. The steps that you have to follow are:

1. As you start the computer on the DOS mode you see C:\> on the top left corner of the

monitor. Insert system disk # 1 in drive A.

2. Type A: The prompt will change to A:\>

3. Type dBASE and press ENTER key.

4. After a few seconds the screen will display details of the dBASE III + package like name,

version, etc. The bottom of the screen will contain the message,

‘INSERT SYSTEM DISK # 2 AND PRESS ENTER KEY’.

5. Remove the system disk # 1 from drive A and insert system disk # 2.

6. Press ENTER key. After a few seconds main menu of dBASE will appear on screen.

As the computer displays the main menu of dBASE III + your monitor will look somewhat like Fig.

20.2.

Fig. 20.2

(given at the end)

IN-TEXT QUESTIONS 1

1. Define field, record, file, and database briefly.

2. Name three DBMS packages.


(a) In database there can be six categories of fields.

(b) A database is a collection of logically related records.

(c) Date of birth is character type field.

(d) You can invoke dBASE III + either from Hard disk or from floppy drives.

(e) Paradox is a DBMS package.

20.5 HOW TO CREATE A DATABASE?

137

20.5.1 Creating a Database

When you want to create a database you have to take care of the following steps: You have to specify

the database file structure such as

File name

Field names

Field types

Field widths

Decimal places (for numeric fields only)

1. Saving the database structure

2. Entering data into the file as records

20.5.2 File Name

File name can be up to eight characters with additional three characters extension. For

example, you can give a file name NAMELIST.DBF to your database file.

It must begin with an alphabet

Can include numbers, and the underscore character ( _)

It cannot contain blank space.

20.5.3 Field names

Can be up to 10 characters long

Can start only with an alphabet

Can contain digits in between

Cannot contain any special character except the underscore ( _ ).

20.5.3 Field Types and Widths

In the beginning we had mentioned that there are five types of fields. Let us discuss them in detail.

1. Character: This type of field contains textual matter. For example, name, address, special

symbols, numbers and blank spaces. Character field can contain up to 256 characters or bytes. In

Fig. 20.1 the fields Name, Address, Sex and Subjects are character types.

2. Numeric: This type of field contains integers or decimal numbers, either positive or negative. The

maximum length of numeric field is up to 19 digits long.

3. Date: Date fields are 8 characters long. It is in the form of MM/DD/YY where MM is the month,

DD is the day of the month and YY is the year. In Fig. 20.1 the field Date of Birth is of date type.

4. Logical: It contains either a 'true' or 'false' (YES or NO) value. Its length is one character or one

byte.

138

5. Memo: Memo fields are used to store large block of text or tabular information. During data entry

it is activated by pressing CTRL+HOME and completed by pressing CTRL+END. The field

width of memo field is upto 5000 characters or bytes.

In order to create a new database you have to give the CREATE command at the dot prompt (see, Fig.

20.2). Let us create a new database file NOS. You have to type

. CREATE

and press ENTER.

On the screen you will find the following message:

Enter the name of the new file:

You have to type a file name, say, NOS and press ENTER. Remember that file name should not be

more than eight characters in length. When you enter the file name you will see a screen as in Fig.

20.3. Here you have to specify the structure of your database. Remember you can type commands

either in lower case or in upper case; dBASE III Plus does not distinguish between the two. Another

point to remember is that in dBASE III Plus you can write the first four alphabets of a command

instead of writing the whole command. For example, in place of CREATE if you can write CREA.

Bytes remaining: 4000

CURSOR

Char:

Word: Home End

Pan: ^ ^

INSERT

Char: Ins

Field: ^N

Help: F1

DELETE

Char: Del

Word: ^Y

Field: Û

Up a Field:

Down a Field:

Exit/Save: Ênd

Abort: Esc

Filed Name Type Width Dec Filed Name Type Width Dec

1. . . Character . . . .

CREATE <C:> NOS Field: 1/1 |

Enter the Field Name.

139

Field names begin with a letter and may contain letters, digits and under scores

Fig. 20.3

Suppose the name of the first field is ROLLNO. Hence you have to type in ROLLNO against the

highlighted space below field name and press ENTER. The cursor will jump automatically to the

column Type. Here by default the Field type is 'Character'. You can change it to other field types by

typing the first alphabet of the field type you want. For example:

C for character, N for numeric, D for date, L for logic and M for memo. For ROLLNO the field type

is Numeric. Hence you type in N. The cursor automatically moves in to the column Width. Here you

have to specify the number of digits the field ROLLNO has and press the RIGHT ARROW key.

Cursor will move to the last column Dec asking you to specify the number of decimal places the field

contains. Since ROLLNO does not contain any decimal number you have to press ENTER only. The

cursor will move automatically to the second record. Your screen will look like Fig. 20.4.

Here you have to give specifications for the second record and go on till all records are specified.


CURSOR

Char:

Word: Home End

Pan: ^ ^

INSERT

Char: Ins

Field: ^N

Help: F1

DELETE

Char: Del

Word: ^Y

Field: Û

Up a Field:

Down a Field:

Exit/Save:

Ênd

Abort:

Esc


1. .ROLLNO . Numeric .5 . . .

2. . . Character . . . .

CREATE <C:> NOS Field: 2/2

140

Enter the Field Name.

Field names begin with a letter and may contain letters, digits and under scores

Fig. 20.4

Once you have created a structure you want to use, you can save it in your disk.

Then you have to save the structure by pressing CTRL+W or CTRL+END

At this point the computer will prompt you

Press ENTER to confirm. Any other key to resume.

Once you press the ENTER key you will find another message:

Input data records now? (Y/N)

If you want to type in data then press Y. The computer screen will look like Fig. 20.5.


CURSOR

Char:

Word: Home End

Pan: ^ ^

INSERT

Char: Ins

Field: ^N

Help: F1

DELETE

Char: Del

Word: ^Y

Field: Û

Up a Field:

Down a Field:

Exit/Save: Ênd

Abort: Esc

ROLLNO: . .

NAME: . .

BIRTH DATE: . .

SUBJECTS: . .

CREATE <C:> NOS REC:NONE

141

Fig. 20.5

Now you can enter data on the screen. As you know, data on a particular student is a record. Thus you

have to enter as many records as you want. After completion of data entry you have to save it by

pressing CTRL and END keys together (CTRL+END). Another method of saving a database is by

pressing CTRL and W keys together (CTRL+W). If you want to quit dBASE without saving then you

have to press ESC or CTRL+Q. At this point dBASE asks you if you really want to “Abort Editing?

(Y/N)”. You have to type Y for yes and N for no. If you type Y you will return to dBASE dot prompt

and if you type N you can continue editing of your file.

20.6 OPENING AN EXISTING FILE

Just as you open a book in order to read it, a database file, existing on a floppy or a hard disk, also has

to be opened. The USE command opens an existing database file so that it can be used for querying,

reporting or editing.

Suppose you want to open the earlier created file BIODATA for further modification. You give the

command:

.USE NOS

Note that when you save a database file in dBASE the computer gives an extension .DBF along with

the file name. While opening a file, dBASEIII+ assumes it to be a .DBF file.

The USE command assumes that the file is to be loaded from the default or active drive, i.e. the drive

from which dBASE was invoked. If the file is on a floppy, you have to instruct dBASE III+ to make

the A drive as the active work drive, rather than the C drive. This can be done by the following

command:

. SET DEFAULT TO A:

On selecting a work drive, all subsequent commands will apply to that drive.

20.6.1 Viewing the Contents of the File

After opening the file BIODATA you may like to see its content. This you can do by the LIST

command.

.List

The screen will look like Fig. 20.6.

. list

142

No database is in USE. Enter file name: biodata

Record# NAME SEX AGE

1 Anant m 25

2 Babloo m 13

3 Manju f 30

4 Sibu m 12

5 Soma f 8

.

Command Line <C:>BIODATA Rec: EOF/5

Type a command (or ASSIST) and press the ENTER key.

Enter a dBASE III PLUS command.

Fig. 20.6

Since there are 5 records only in the database we are dealing with all the records are visible on a

single screen. When all the records cannot come on a single screen the records scroll down and you

cannot see the records in the beginning. In order to overcome this problem you have to use the

DISPLAY ALL command.

The .Display All command displays a screen full of records and pauses, until the user presses a key to

continue.

Press the F1 key for HELP.

. use biodata

. display


1 Anant m 25

.

Command Line |<C:>|BIODATA |Rec: 1/5 | |



Fig. 20.7

143

20.7 ADDING RECORDS

Suppose some new students have taken admission in National Open School. You want to add these

student records to the existing file BIODATA. In order to do so you have to use the APPEND

command. The APPEND command displays a blank record for data entry. Once the data has been

entered, it presents another blank record. This process continues till the user presses CTRL+END

CURSOR

Char:

Word: Home End

Pan: ^ ^

INSERT

Char: Ins

Field: ^N

Help: F1

DELETE

Char: Del

Word: ^Y

Field: Û

Up a Field:

Down a Field:

Exit/Save: Ênd

Abort: Esc

NAME . .

SEX . .

AGE . .

.

APPEND <C:> BIODATA Rec: EOF/5 |

Fig. 20.8

144

IN-TEXT QUESTIONS 2

1. What are the different types of fields in dBASEIII+.

2. What is the usefulness of the following commands: APPEND, LIST, CREATE.


(a) The field name can be a maximum of 10 characters.

(b) The maximum width for a character type field is 250.

(c) The width of a logical field is 2 digits.

(d) Character field is used for mathematical calculation.

(e) A field name should always start with an alphabet.


In this lesson we discussed the concept of database and the software available to manage it. The

different methods to invoke dBASE III Plus are discussed. We have also explained the different types

of fields in a database. Now you should be in a position to create a new database, add records to an

existing database and see the contents of a database.


1. What are the different methods to start dBASEIII+ ?

1. Explain in brief the following field types:

Character field, Date field, Numeric field and Memo field.

2. What are the advantages of dBASEIII+?

3. How do you add records a database?


IN-TEXT QUESTIONS 1

1. Each piece of information in database is called a Field. Field is the smallest unit in a database. All

the related fields for a particular event is called a Record.

2. FoxBASE, dBASE, Clipper

3. (a) False (b) True (c) False (d) True (e) True

IN-TEXT QUESTIONS 2

1. There are five types of fields in database. They are Character, Numeric, Date, Logic and Memo.

2. Create command creates a new database. List command displays all the records in a database. The

Append command displays a blank record for data entry.

4. (a) True (b) False (c) False (d) False (e) True

145

146

dBASE III + version 1.0 IBM/MSDOS

Copyright © Ashton-Tate 1984, 1985, 1986. All Rights Reserved.

dBASE, dBASE III, dBASE III +, and Ashton-Tate

are trademarks of Ashton-Tate

You may use the dBASE III + software and printed materials in the dBASE III

+ software package under the terms of the dBASE III + Software License

Agreement. In summary, Ashton-Tate grants you a paid-up, non-transferable,

personal license to use dBASE III + on one microcomputer or workstation. You

do not become the owner of the package, nor do you have the right to copy or

alter the software or printed materials. You are legally accountable for any

violation of the License Agreement or of copyright, trademark, or trade secret

laws.

Press the F1 key for HELP

Command Line |<C:>|


Enter a dBASE III + command.

Fig. 20.2

147

Dot prompt

LESSON 20

INTRODUCTION TO DATABASE

1.1 INTRODUCTION

20.1 OBJECTIVES

20.2 HOW TO START dBASE III PLUS?

LESSON 21

ARRANGING RECORDS OF A DATABASE

21. 1 INTRODUCTION

Organizing a database means arranging individual records so that they appear in a sequence that

makes a proper sense and helps you to work with database efficiently. The concept can be appreciated

by taking an example of telephone directory. Imagine a situation where names in the directory are not

arranged alphabetically. This will create a mess and take much longer time to find a particular name

in the directory.

21. 2 OBJECTIVES

At the end of this lesson you would be able to

use the SORT and INDEX commands to organise records of a database

differentiate between FIND and SEEK commands

count the number of records in a database

modify a database

DELETE records in a database

RECALL and REPLACE records in a database

21. 3 DATABASE ORGANISATION

Information must be organized before you can make much sense of it. The elements of a database

structure - field name, type, and size are all intended to organise within each record. There are two

ways to organize records in database. One is INDEXING and the other is SORTING. Before sorting

a database you make sure that the database you want to sort is current:

21. 3. 1 SORT Command

The SORT command gives us the ability to copy the record and structure of a database to another

database. Files can be arranged in either ascending order or descending order by using SORT

command. Sort command can be used in multiple fields for data arrangement.

148

This SORT command creates a new database file. But the new file contains records of the original

database file only the order is different. The following examples show the forms of the SORT

command. Let us consider a database file BIODATA, whose structure is shown in Fig. 21. 1

RECORD

NO.

NAME SEX AGE

1 Anant M 25

2 Babloo M 13

3 Manju F 30

4 Sibu M 12

5 Soma F 28

Fig. 21.1

Suppose you want to sort the records in this file in increasing order of the AGE field. You have to

give the command at the dot prompt:

.USE BIODATA and press ENTER

. SORT ON fieldname TO new filename. Thus you have to give the command

. SORT ON AGE TO BIO and press ENTER

Here field name is AGE and the sorted file name is BIO.DBF

To see the contents of the sorted file give the following commands:

. USE BIO.DBF

. LIST

The sorted file BIO. DBF looks like as shown in Fig. 21.2.

149

. use biodata

. sort on age to bio

100% sorted 5 records sorted

. use bio

. list


4 Sibu m 12

2 Babloo m 13

1 Anant m 25

5 Soma f 28

3 Manju f 30

Fig. 21.2

Here you notice one thing that BIO.DBF is a new file. In this new file, the record numbers given by

database is in a new order. But Age field is in sequence, because you have sorted the BIODATA .DBF

to increasing order of the AGE field. Suppose you want to sort the file in descending order of the

AGE field. Then you have to give the command SORT ON AGE/D TO TEMP .DBF. The new file

TEMP looks like as shown in Fig. 21.3

. use biodata

. sort on age/d to temp

100% sorted 5 Records sorted

. use temp

. list


1 Manju f 30

2 Soma f 28

3 Anant m 25

4 Babloo m 13

5 Sibu m 12

Fig. 21.3

21. 3. 2 INDEX command

150

Index command can also be used to organise a data file. When you index a database, you ask dBASE

to create a separate and smaller file based upon designated fields in the database. The index command

does not create a new database file. It creates an index file for the database with a default extension

(.NDX). Unlike SORT command however INDEX does not permit the user to arrange the data in

descending order. It can also be used to arrange the records in multiple fields. The command structure

for index command is

.USE BIODATA

. INDEX ON field name TO file name

For example, if we index the file biodata.dbf according to field age to the file bioage then the records

in the file biodata.dbf are arranged in ascending order as given in Fig. 21.4

. use biodata

. index on age to bioage

100% indexed 5 Records indexed

. list


4 Sibu m 12

2 Babloo m 13

1 Anant m 25

5 Soma f 28

3 Manju f 30

Fig 21.4

DIFFERENCE BETWEEN SORT AND INDEX COMMAND

Sort Command Index command

Creates a new database file Does not create a new file

151

Arranges the records in ascending and

descending order

Arranges the records only in ascending order

File extension is .DBF File extension is .NDX

Slower than index command Faster than sort command

Renumbers records Does not renumber records

21.3.3 FIND and SEEK Commands

The FIND and SEEK commands both are used in indexed database. FIND operates with character

strings, while SEEK operates with either character string or numeric values. If SEEK operates with a

character string the string must be enclosed in a single or double quotes or square bracket Let us take

some examples

. USE BIODATA

. INDEX ON AGE TO BIOAGE

. USE BIODATA INDEX BIOAGE

. FIND 30

. DISPLAY

The screen will look like this

. use biodata


. use biodata index bioage

. find 30

. display


3 Manju f 30

Fig 21.5

The FIND command will move the record pointer to the first record which matches with find query

and the DISPLAY command will display it on the screen.

The SEEK command like FIND command also works only with an index file. When you SEEK

command with strings, you must use quotes. Consider the previous example, to SEEK the NAME

Manju, you must give the command

. USE BIODATA

. INDEX ON AGE TO BIOAGE

. USE BIODATA INDEX BIOAGE

. SEEK 30

152

. DISPLAY

The screen will look like this

.use biodata


. use biodata index bioage

. seek 30

. display


3 Manju f 30

Fig 21.6

The main difference between SEEK and FIND commands is that SEEK command will not work with

macros but FIND command is used in macros.

21.3.4 Counting Command

The COUNT command helps in finding the number of records in the active database that meet a

given condition.

. USE BIODATA

. COUNT FOR AGE> 13

The screen will appear as follows:

. use biodata

. count for age >13

3 records

. count

5 records

Fig 21.7

The COUNT command, without any condition, gives the total number of records in the active

database file.

. COUNT

153

The computer prompts

5 RECORDS

21.3.5 LOCATE Command

The LOCATE command is used to find the records in a database which satisfy certain conditions. The

general form of LOCATE command is

. LOCATE [scope] FOR [condition]

Suppose you give the command

. USE BIODATA

. LOCATE FOR AGE =25

The computer will prompt

RECORD =1

Your screen will appear like this

. use biodata

. locate for age=25

Record = 1

Fig 21.8

For displaying that particular record in a database give the command DISPLAY and if you want to

continue the search give the command CONTINUE along with LOCATE command. Your screen will

appear like this

. use biodata

. locate for age=30

Record = 3

. continue

End of LOCATE scope

154

Command Line ¦<C:>¦BIODATA ¦Rec: EOF/5 ¦ ¦


Fig. 21.9

IN-TEXT QUESTIONS 1

1. What is the difference between SORT and INDEX command?

2. What is the usefulness of FIND and SEEK commands?

3. Define the following command with a suitable example

(a) COUNT (b) LOCATE

21. 4 MODIFYING A DATABASE

Modifying a database is almost as easy as creating a database. You begin with an existing structure

and want to modify the database by

Inserting a new field

Deleting an existing field

Inserting a new record

Deleting a record permanently

Let us explain the steps by taking our previous file BIODATA. Begin with opening the file.

. USE BIODATA

. EDIT 5

CURSOR

Char:

Word: Home End

Pan: ^ ^

INSERT

Char: Ins

Field: ^N

Help: F1

DELETE

Char: Del

Word: ^Y

Field: Û

Up a Field:

Down a Field:

Exit/Save: Ênd

Abort: Esc

NAME Soma

SEX f

155

AGE 28

EDIT ¦<C:>¦BIODATA ¦Rec: 5/5

Fig. 21.10

After making the desired changes, pressing Ctrl+W saves the changes and exits to the prompt.

21 .4. 1 The Record Pointer

How did the EDIT command display only the 5th record? This can be explained by the concept of a

record pointer that is maintained for each file opened by dBASEIII+. When the file is open the

pointer points to the first record in the file and moves to the other records after a command has been

given. For example, with the LIST command, the record pointer moves to the end of the file, since it

moves successively from the first record to the last record. The current record (i.e., the record on

which the pointer is positioned currently) can be displayed by giving the command. DISPLAY. This

command is used to position a particular record, which is to be displayed.

. DISPLAY

DISPLAY [ALL!RECORD<recordno. >]

[<expr_list>] [FOR<expl.>] [TO PRINT]

where:

<expr_list> is a list fields or expressions.

<expl.> is a condition.

.USE BIODATA

.DISPLAY

dBASE will display only the first record along with header which we have discussed earlier.

Let us consider the following example

dBASE will display the 4th record in the file along with header.

. use biodata

. goto 4

. display


4 Sibu m 12

156

.

Fig 21.11

The GOTO command followed by the record number moves the record pointer to a specified record.

. GOTO 5

This command will position the pointer on the 5th record.

. GOTO<expN>

where <expN> is the record number.

. use biodata

. goto 5

. display


5 Soma f 28

.

Fig 21.12

21. 4. 2 EDIT Command

Similarly, on giving the command EDIT 5, the record pointer moves to the 5 th record and displays it

for modification.

To summarise, the steps involved in modifying a database, using the EDIT command are:

Open the file by the command USE File Name

Access the record(s) to be modified.

Make the required changes in the records.

Save the changes by pressing <Ctrl>+<W>.

This command positions the record pointer at the required record and displays it for modification

157

EDIT [ALL![RECORD]<record no. >]

[FIELDS<fieldlist>] [FOR<expl>]

Where:

<fieldlist> is a list of fields to be edited

<expL. > is a condition.

Now we open BIODATA by the command USE

.USE BIODATA

. EDIT

The screen looks like this

CURSOR

Char:

Word: Home End

Pan: ^ ^

INSERT

Char: Ins

Field: ^N

Help: F1

DELETE

Char: Del

Word: ^Y

Field: Û

Up a Field:

Down a Field:

Exit/Save: Ênd

Abort: Esc

NAME Soma

SEX f

AGE 28

EDIT ¦<C:>¦BIODATA ¦Rec: 5/5 ¦ ¦

Fig. 21.13

21. 4. 3 REPLACE command

The REPLACE command is used to REPLACE the contents of one or more specified field either the

current record or all record, depending on the form of the command.

. REPLACE ALL

Syntax:

REPLACE [ALL] <field> WITH <expr>

[FOR<expl>]

Where:

158

<field> is the field to be replaced

<expr> is the expression to replace the field

<expl> is a condition.

21. 4. 4 BROWSE Command

BROWSE command gives an option of adding new records. The BROWSE command also provides

the option of displaying and modifying selective fields. Once you make changes through BROWSE

command you can save the changes and exit to the dot prompt by pressing Ctrl + W. Consider the

following example:

. USE BIODATA

. BROWSE

Immediately dBASE will display a screenful of records as shown in Fig. 21.14

The difference between BROWSE and EDIT Command is that several records are viewed

simultaneously using BROWSE, while one record is displayed at a time when EDIT is used.

CURSOR

Char:

Word: Home End

Pan: ^ ^

INSERT

Char: Ins

Field: ^N

Help: F1

DELETE

Char: Del

Word: ^Y

Field: Û

Up a Field:

Down a Field:

Exit/Save: Ênd

Abort: Esc

NAME SEX AGE

Anant m 25

Babloo m 13

Manju f 30

Sibu m 12

Soma f 28

BROWSE ¦<C:>¦BIODATA ¦Rec: 1/5 ¦ ¦

View and edit fields.

Fig. 21.14

21. 5 MODIFY STRUCTURE

The MODIFY STRUCTURE command helps to change the structure of an active database file. The

command:

159

. MODIFY STRUCTURE

displays the structure of the database file as shown in figure 21.15 . After adding the field to the file

save the modified structure by pressing <Ctrl>+<W>. The MODIFY STRUCTURE command also

allows deleting fields or changing the field types and widths. You should keep in mind that if the field

widths are reduced, the data in that field may be lost. Hence changes to existing fields must be made

with proper care.

Let us consider the following example.


CURSOR

Char:

Word: Home End

Pan: ^ ^

INSERT

Char: Ins

Field: ^N

Help: F1

DELETE

Char: Del

Word: ^Y

Field: Û

Up a Field:

Down a Field:

Exit/Save: Ênd

Abort: Esc


1 NAME Character 10

2 SEX Character 1

3 AGE Numeric 2 0

MODIFY STRUCTURE |<C:>|BIODATA |Field: 1/3 | |

Enter the field name.

Field names begin with a letter and may contain letters, digits and underscores

Fig. 21.15

21. 6 MORE ON QUERIES

Instead of giving the List to Print command with each and every query, the printer can be activated to

print the command as well as the output of the command. The command that can be given to activate

the printer is as follows:

. SET PRINT ON

. LIST

To deactivate the printer the command is:

160

. SET PRINT OFF

21.6.1 Deleting Records

The delete command marks the current record for deletion. When the records are marked for deletion

they are not transferred during copy and sort operation. Now we will discuss how delete command is

used in different ways.

. DELETE RECORD 5 <marks record 5 for deletion>.

1 records deleted

The DELETE command also provides the following options:

OPTION DESCRIPTION

DELETE ALL Mark all records for deletion

DELETE FOR Mark selective records for deletion

DELETE FILE ABC.FRM Delete file ABC.FRM on logged disk.

DELETE NEXT 4 Mark next 4 records for deletion.

Now delete all the records in the active database file BIODATA. You will find an asterisk (*) against

the records marked for deletion.

. use biodata

. delete all

5 records deleted

. list


1 *Anant m 25

2 *Babloo m 13

3 *Manju f 30

4 *Sibu m 12

5 *Soma f 28

.

161


Type a command (or ASSIST) and press the ENTER key (-+).


Fig. 21.16

In this example we delete the next four records from the active database file.

. use biodata

. delete next 4

4 records deleted

. list


1 *Anant m 25

2 *Babloo m 13

3 *Manju f 30

4 *Sibu m 12

5 Soma f 28




Fig. 21.17

21.6.2 PACK Command

This command removes records permanently from the database file. Once packed a record cannot be

recovered. Deleting records in dBASEIII+ is a two step process. The records are first marked for

deletion with the DELETE command, and then removed permanently from the file by PACK

command

Let us take the following example

. USE BIODATA

. DELETE 3

. PACK

Next if you give LIST command then you will not find record 3 in database.

162

21.6.3 RECALL Command

The RECALL command is used to unmark those records that were marked for deletion with DELETE

command. Like DELETE command, RECALL has several forms.

OPTION DESCRIPTION

. RECALL RECORD 4 Unmark record 4 for deletion

. RECALL NEXT 3 Unmark the next 3 records for deletion

. RECALL ALL Unmark all records within the database for deletion.

Now we recall all the records marked for deletion in the active database file BIODATA. Notice that

the RECALL command unmarks the records, which were marked for deletion earlier.

. use biodata

. recall all

5 records recalled

. list


1 Anant m 25

2 Babloo m 13

3 Manju f 30

4 Sibu m 12

5 Soma f 28

.




Fig. 21.18

21. 7 CLOSING AN OPEN DATABASE FILE

The USE commands without file name closes an open database file. Open database can also be closed

with the QUIT, CLEAR ALL, CLOSE DATABASE and CLOSE ALL commands.

163

IN -TEXT QUESTIONS 2

1. Differentiate between EDIT and BROWSE commands.

2. Bring out the uses of the following commands

DELETE

PACK

RECALL

REPLACE

USE

3. Choose the correct answer

(a) Delete command

(i) marks the record for deletion

(ii) append the record

(iii) change the number

(iv) none of the above

(b) To add record at the end of the database, you would use

(i) continue

(ii) list

(iii) append

(iv) use

(c) Which of the following command physically remove the records

(i) change

(ii) modify

(iii) pack


(d) Which of the following command is used to close a database file.

(i) stop

(ii) use

(iii) start


(e) The modify structure command helps

(i) to change the structure of an active database file.

(ii) to remove the structure

164

(iii) to name the structure



In this lesson we discussed the procedures of organising a database. In this process we distinguished

between SORT and INDEX commands, FIND and SEEK commands, DELETE and PACK

commands, BROWSE and EDIT commands. Now you should be in a position to count the number of

records in a database and modify structure of a database.


1. What are the different methods of data organisation.? Explain briefly.

2. Write short notes on SEEK, FIND, GOTO, EDIT, RECALL and PACK commands.

3. Define SORT and INDEX command with suitable example.

4. What are the different steps involved in modifying a database, while using EDIT command?

5. Define COUNT command with example.


IN-TEXT QUESTIONS 1

1. Files can be arranged in either ascending order or descending order by using SORT command.

But incase of INDEX command you can arrange the file only ascending order. Index command

does not create a new database file. But SORT command creates a new database file.

2. FIND operates with character strings, while SEEK operates with either character string or

numeric values.

3. (a) The COUNT command helps in finding the number of records in the active database that

meet a given condition. Example:

. USE NAME

. COUNT FOR AGE> 11

(b) The LOCATE command is used to find the records in a database which satisfy certain conditions.

Example:

. USE BIODATA

. LOCATE FOR AGE=18

IN-TEXT QUESTIONS 2

1. EDIT command displays one a particular record that is the record at the cursor position. But

BROWSE command displays all the records in the database file.

165

2. DELETE: marks the record for deletion.

PACK: Permanently deletes the records from the database file, which were earlier marked for

deletion by DELETE command.

RECALL: Unmarks the record marked earlier.

REPLACE: used to REPLACE the contents of one or more specified field

USE: Closes the active database file.

3. (a) i

(b) iii

(c) iii

(d) ii

(e) i

LESSON 22

HANDLING MULTIPLE FILES

22.1 INTRODUCTION

Many times we have to combine data from more than one file. In such situations we have to handle

multiple databases. Another point is that the data contained in a database file is not suitable for

presentation. It has to be put in a presentable format. This aspect of dBASE III Plus is possible

through the report form facilities of a database.

22.2 OBJECTIVES

After going through this lesson you should be in a position to

explain the concept of multiple database

understand work area

relate more than two databases

create a report file from a database

print a report file

22.3 MULTIPLE FILE HANDLING

In the previous two lessons we have discussed about the commands to manipulate and retrieve data

from a single database file. But at times we may need to combine data from different database files for

purpose of manipulation and reporting. dBASE provides scope for handling up to 10 database files

open at the same time and access data from them. This is called Multiple File Handling.

22.3.1 Characteristics of Multiple Files

166

Before we discuss the procedure of handling more than one-database files let us look into the

characteristics of multiple database files. Let us start with two files (dB1 and dB2). We may come

across the following situations.

Situation 1: The number of records in both database files dB1 and dB2 is the same. The number of

fields and the type of fields are the same.

Situation 2: The number of records in both dB1 and dB2 is same. The number of fields is same but

type of fields is different.

Situation 3: The number of records is different. But number of fields and type of fields is the same.

Situation 4: The number of records and number of fields are different. But there is at least one field

which is common to both dB1 and dB2. This common field is called the Key Field.

22.3.2 Types of Operations in Multiple File Handling

Let us look in to the type of work that we may require while handling two database files:

We want to access data from both dB1 and dB2 at the same time.

We want to create a database file dB3 by combining i) all the fields in the records of dB1 and

dB2, ii) selected fields from the records of dB1 and dB2.

We may require updating of one or more fields in a file called the master file taking the data from

another file called the transaction file. Let us take dB1 as the master file and dB2 as the

transaction file. So we take data from dB2 to update dB1.

22.3.3 Selecting Work Areas for Different Files

When a database file is opened by the USE command, dBASE allots a work area for that file. When

we use only one file, we do not need to give any reference to the work area. But when we use multiple

files (up to 10 files), we have to specify the areas in which the different files will work. The SELECT

command is used to allot work areas for different files in dBASE. dBASE assigns numbers 1 to 10 or

characters A to J to these work areas. The general form of the SELECT command is

.SELECT workarea

.USE filename

Suppose we have two database files, dB1 and dB2. For allotting the work areas A and B for the two

files, we give the commands as follows:

. SELECT A

. USE dB1

. SELECT B

. USE dB2

167

On the other hand we may allot numbers to the work areas. For allotting the work areas 1 and 2 to the

files dB1 and dB2, we give the commands as follows:

. SELECT 1

. USE dB1

. SELECT 2

. USE dB2

In the example we have taken two database files but you can take any number (up to 10) of database

files. In place of dB1 and dB2 you can give any other file name.

22.4 ACTIVE AND NON-ACTIVE FILES

When several files are in use by the SELECT command, the file that is selected last is called the

active file and other files are called non-active files. When we allot work area to multiple files the file

selected last becomes the active file. In the last example, the file dB2 is selected last and so it is the

active file. Suppose you have a field by name AGE in dB2. This can be referenced simply as AGE

(note that AGE is a field in the active file.). Suppose you have a field by name STDNAME in the file

dB1. Then this field is referenced by writing as A-> STDNAME (note that when we refer to a field in

the non-active file we prefix it with the work area allotted to the no-active file). The symbol (->) 'a

minus sign followed by a greater than symbol' is used to establish the relation between the non-active

database file name and its field name.

22.4.1 How to Switch the File Status from Active to Non-Active?

You can make any non-active file, active by giving the command

.SELECT non-active-file-name.

Suppose in the example considered earlier if we give the command

.SELECT A

The file dB1 in the work area 1 becomes active and the file dB2 becomes non-active.

In this case the file in the work area 1 is made active currently. One must not give the USE command

for making a file active. The USE command opens a file and a file that is once opened must not be

again opened, since it is a syntax error. The SELECT Command does not open a file but simply

switches between the work areas. Thus we see that the SELECT command enables us to access fields

or data from as many as 10 database files.

22.4.2 ALIAS Names for Database Files

168

dBASE has got a facility to give an alternate or an ALIAS name to a database file dB1. The SELECT

command is written as follows:

.SELECT A

.USE dB1 ALIAS biofile

If at any time you want to make the file dB1 active you can give the command

.SELECT biofile

The above command automatically puts the file dB1 in the work area A and makes it active. Without

making a file active, you can display any particular field from a non-active database can by giving

command as follows:

. DISPLAY alias name ->field-name (if you have given an alias name)

or

. DISPLAY work area name -> field-name (if you have not given an alias name)

You already know that the symbol (->) is used to establish the relation between the database name (or

its alias name) and its field names. For the field STDNAME in the active file dB1, we can display the

field by the command

. DISPLAY stdname

If no alias names are given by the user, dBASE will assume the filename itself as the alias name.

Suppose you give the following commands:

. CLOSE ALL (This command closes all files)

. SELECT B (This will select work area B)

. USE dB2 (This will assign work area B to file dB2)

. SELECT A (This will select work area A)

. USE dB1 (This will assign work area A to file dB1)

. DISPLAY STATUS

On the monitor you will see the status as follows:

Currently Selected Database

Select Area : A, Database in Use: A : dB1.dbf alias : dB1

Select Area : B, Database in Use: A : dB2.dbf alias : dB2

Fig 22.1

22.4.3 The SET RELATION TO Command

This command is used to link two database files with or without a common field between them.

Suppose you have to link two database files dB1 and dB2. The contents of these two are as shown in

the Fig. 22.2 and Fig. 22.3 respectively.

169

. USE dB1

. LIST

Record# CITY STATE SALARY

1 Cuttack Orissa 2500

2 Delhi Delhi 1350

3 Madras Tamilnadu 3000

4 Bombay Maharastra 1280

5 Chandigarh Punjab 8000

.

Command Line ||<C:>|| dB1 || Rec: EOF/5 || ||

Type a command (or ASSIST) and press the ENTER key ().


Fig. 22.2

. USE dB2

. LIST

Record# NAME AGE

1 Anant 25

2 Babloo 23

3 Manju 30

4 Sibu 22

5 Soma 28

.

Command Line <C:>dB2 Rec: EOF/5



Fig. 22.3

In this example the two files have the same number of records but completely different field types.

The only relation which we see between these two files is that there is one to one correspondence

between the record number of the two files. We will now link the two files using this common feature

between them. The commands are given as follows:

170

.SELECT B

. USE dB2

. SELECT A

. USE dB1

. SET RELATION TO RECNO( ) INTO dB2

. LIST CITY, STATE, SALARY, B->NAME, B->AGE

The listing of the combined file looks as shown in the Fig. 22.4. In the above case all the fields and all

the records are listed.

Record# CITY STATE SALARY NAME AGE

1 Cuttack Orissa 2500 Anant 25

2 Delhi Delhi 1350 Babloo 23

3 Madras Tamilnadu 3000 Manju 30

4 Bombay Maharastra 280 Sibu 22

5 Chandigarh Punjab 8000 Soma 28

.

Command Line <C:>dB1 Rec: EOF/5



Fig. 22.4

IN-TEXT QUESTIONS 1

1. How many databases can be used simultaneously in dBASE III+?

2. Give the name of the first work area used in dBASE III+.

3. Which command is used to select a work area in dBASE III+?

4. Differentiate between active and non-active files.

5. Choose the correct answer:

(a) What is the maximum number of work areas that can be used in dBASE

(i) 20 (ii) 10 (iii) 5 (iv) 9

(b) The first work area in dBASE is referred as

(i) W -area (ii) ‘A’ (iii) ‘A-J’ (iv) none of the above

171

22.5 REPORT FORM

So far we have covered listing and modification of raw data. We also know how to link two files. But

in all the cases discussed so far the result we get is not formatted in a presentable manner. We cannot

take a print out and submit it straight away. The result we generate has to be presented in a suitable

form, as we will see below. Such a task is possible through the report form.

Report form files are created and modified with the CREATE or MODIFY REPORT command.

Before the command is used, a database file must be in use. The field characteristics within the

selected database file are used to help you design your report form.

Both .DBF and .VUE files are used with the CREATE or MODIFY REPORT command. Once

designed, the REPORT FORM filename command is used to reproduce the report on your screen. If

you add the TO PRINT clause to the REPORT FORM command, the report is printed as it is

displayed on your screen.

The default extension given a report form file is .FRM. However, you can assign a different extension

upon creation, or you can use the RENAME command rename the file extension.

22.6 HOW TO GENERATE THE REPORT FORM?

Open the file BIODATA and give the CREATE REPORT command. Instead of the word CREATE

you can use the word MODIFY also.

. USE BIODATA

. CREATE REPORT

dBASE responds to the above command by displaying the following message:

Enter Report File Name:

You have to type the filename BIO and press ENTER key. dBASE displays a menu screen with five

items in the main menu as follows (see, Fig. 22.5).

Options

Groups

Columns

Locate

Exit

By default the menu item OPTIONS is highlighted. In the menu item OPTIONS there are 9 sub-items

as shown in Fig 22.5. By default the sub-item PAGE TITLE is highlighted. We will discuss about

each of these in detail.

22.6.1 OPTIONS

There are nine sub-items under the menu item OPTIONS. They are discussed below.

172

Options Groups Columns Locate Exit 01:43:57 pm

Page title .

Page width (positions) 80

Left margin 8

Right margin 0

Lines per page 58

Double space report No

Page eject before printing Yes

Page eject after printing No

Plain page No

CURSOR

Char:

Word: Home End

Pan: ^ ^

INSERT

Char: Ins

Field: ^N

Help: F1

DELETE

Char: Del

Word: ^Y

Field: Û

Up a Field:

Down a Field:

Exit/Save:

Ênd

Abort:

Esc

CREATE REPORT |<C:> | BIO.FRM | Opt: 1/9 | |

Position selection bar - . Select - . Leave menu - .

Enter up to four lines of text to be displayed at the top of each report page.

Fig. 22.5

1. Page Title: By default the cursor is over the page title item. On pressing the control key CTRL a

window opens up by the side of the option menu box where you want to enter titles of further

report. The titles can be up to lines of text, each line can be up to 60 characters.

2. Page width: This is used to specify the number of characters to be printed on each line of the

report. The default is 80 characters.

173

3. Left margin: In this option you can specify the number of characters required as left margin. The

default is 8 characters.

4. Right margin: Used to specify the number of characters required for right margin. The default is

0.

5. Number of Lines/Page: Used to specify the number of lines on every page of the report. The

default is 58 lines.

6. Double Space Report (Y/N): Used to specify double spacing in the report. Default is single

space.

7. Page Eject before Printing (Y/N): Used to skip to a new page before printing. By default a page

is skipped before a report is printed.

8. Page Eject after Printing (Y/N): Used to skip a page after the report is printed. By default it

does not skip a page after a report is printed.

9. Plain page (Y/N): Used to suppress/display page number and date. The default is NO which

suggests that page number, page title and date are displayed on each page. By typing Y (for Yes)

you will get the page title only on the first page. But the page number and date will not be printed.

22.6.2 GROUPS

After setting the above options now let us take the cursor to the second menu item GROUPS by the

right arrow key. The contents of the screen will change as shown in Fig. 22.6. There are six sub-items

under the menu item GROUPS. Each of them is described below.

1. Group on expression: This sub-item is highlighted by default (see Fig. 22.6). This item groups

the records having a common value in a key field. New groups are started when a new value is

encountered. The key field is selected in the COLUMNS menu selection.

2. Group heading: This let you enter a report heading that is displayed as each new group is

encountered and displayed.

3. Summary report only: The default option under this item is NO. This includes all records in the

report. If you change it to YES detail information is not provided and only subtotals are provided.

4. Page Eject after group: YES, This causes a form feed after each group is printed. The option

NO prints the groups together.

5. Sub-group on expression: This selection lets you specify a secondary level of grouping for sub-

groups within groups. Like the main group, sub-groups should also be indexed or sorted.

6. Sub-group heading: Lets you enter a report heading that is displayed as each new sub-group is

encountered and displayed.


174

Group on expression .

Group heading

Summary report only No

Page eject after group Yes

Sub-group on expression

Sub-group heading

.

CREATE REPORT ¦<C:>¦ BIO.FRM ¦ Opt: 1/6 ¦ ¦


Enter a field or expression on which to break for the first level of subtotals.

Fig. 22.6

22.6.3 COLUMNS

Now let us discuss the menu item COLUMNS. You can select this item by the right arrow key. The

screen will be displayed like Fig. 22.7. There are five sub-items under COLUMNS. Each of them is

discussed below.

1. Contents: Enter the field name for each column. You can press ENTER or F10 key to display a

field list. Select and return to the Column menu with the Right or Left Arrow key.

2. Heading : Lets you enter up to four 59-character lines as column headings.

3. Width: The column widths default to the field width or heading width, whichever is larger. You

can modify the width by typing a new field.

4. Decimal places: Uses the file structure value. If you enter a smaller number, the displayed result

is rounded. Only applies to numeric fields.

5. Total this column: The default is to print the total at the bottom of the report. Type NO to

suppress printing.

Note that the column specifications must be given for each column. As you fill the items for the

column details, you will find that a REPORT FORMAT box is opened at the lower end in the position

of the cursor control menu. This shows the column heading and the column formats. The following

symbols are used to represent the structure of the report as you enter it.


175

Contents .

Heading

Width 0

Decimal places

Total this column

________Report Format_______________________________________________________

>>>>>>>

CREATE REPORT ¦<C:>¦ BIO.FRM ¦ Column: 1 ¦ ¦

Position selection bar - . Select - . Prev/Next column - Pg Up/Pg Dn.

Enter a field or expression to display in the indicated report column.

Fig. 22.7

22.6.4 LOCATE

The locate menu is provided to help with column definition. This menu item lists the selection that

you made using COLUMNS menu. If you do not define the columns earlier the screen will display

like Fig. 22.8.

Options GroupsColumns Locate Exit 06:25:04 pm

No columns defined

________Report Format_______________________________________________________

>>>>>>>

176

CREATE REPORT ¦<C:>¦ BIO.FRM | Opt: 1/1 ¦ ¦


Step to any column immediately by selecting the column expression.

Fig. 22.8

22.6.5 EXIT MENU

The Exit Menu box has two items as shown in the Fig. 22.9. When SAVE is highlighted, press the

CTRL key. The Report File BIO.FRM is now saved and can be used for printing the report. The

option ABANDON does not save the report file.


Save

Abandon

________Report Format_______________________________________________________

>>>>>>>

CREATE REPORT ¦<C:>¦ BIO.FRM ¦ Opt: 1/2 ¦ ¦

Position selection bar - . Select - . Leave menu -

Exit and save changes.

Fig. 22.9

22.7 PRINTING THE REPORT

To print the Report for selected records a FOR clause or a WHILE clause can be added to the

REPORT command. For saving the Report in a .TXT file, you give a TO filename clause to the

REPORT commands as shown below:

177

.REPORT FORM BIO TO REPO.TXT

The bio report is now stored in the REPO.TXT file. This is an ASCII file and you can see by giving

the TYPE command from DOS prompt.

IN-TEXT QUESTIONS 2

1. Which command is used for report creation?

2. What are the sub-menus of COLUMNS menu?

3. Choose the correct answer

(a) The extension name for Report file is

(i) .NDX (ii) .DBF (iii) .FRM (iv) .PRG

(b) How many items dBASE displays in the main menu of Report generation?

(i) 2 (ii) 7 (iii) 5 (iv) none of the above


In this lesson we covered the basic commands and techniques for displaying data in a formatted

report. The first part of this lesson discusses the multiple database concepts like file handling, work

areas and the commands related to multiple database. The second part covers report generation from a

database file.


1. What are the characteristics of multiple files?

2 How do you switch the File Status from Active to Non-Active form?

3 What is the usefulness of SET RELATION TO command? Explain with example.

4 What are five items or menus while creating a report? Explain in brief.


IN-TEXT QUESTIONS 1

1. 10 databases

178

2. The first work area in database is A.

3. SELECT command

4. The file that is selected last is called the active file and other files are called non-active files.

5. (a) ii (b) ii

IN-TEXT QUESTIONS 2

1. CREATE or MODIFY commands are used in report creation.

2. Contents, Heading, Width, Decimal places, Total This Column are five sub menus of COLUMNS

menu.

3. (a) iii (b) iii

LESSON 23

PROGRAMMING CONCEPT

23.1 INTRODUCTION

By now we are familiar with various dBASE commands and how they are used. Let us consider

another use of dBASE namely in the area of programming. In this lesson we will discuss some

programming constructions in general sense. We will also point out the situations in which they are

used.

We had given a brief idea about the concept of programming while dealing with the lesson on

'Software' in the module 'Computer Fundamentals'. Here we will discuss programming in the context

of dBASE III Plus.

23.2 OBJECTIVES

After going through this lesson you should be in a position to

understand the need of writing programs

identify the important programming commands in dBASE III +

write programs in dBASE III +

identify the types of files created by dBASE III +

23.3 WHAT IS THE NEED OF PROGRAMS?

In the previous three lessons you have learnt so many commands in dBASE. These commands are

given to the computer step by step. We give a second command only after the first command is

executed. But many times the user has to give a set of instructions repeatedly to solve a particular

problem. In such situations writing the same set of instructions every time is time consuming. Another

factor is the chance of committing mistakes while keying in the commands. Hence we need to develop

computer programs and store it in a file.

179

As you know program is a set of instructions given by the user to the computer for solving a problem.

In the programming mode it is possible to write any number of commands together in single file.

When we give a single dBASE command to execute the file all the dBASE commands contained in

the file are executed.

Now let us discuss some of the important commands that are used in programming. They can be

broadly categorised into three areas: Control Commands, Input Commands and Output Commands.

Within these categories we see a number of commands. We will discuss the important ones only in

this lesson.

23.4 CONTROL COMMANDS

The important commands under this heading are

Do While

Exit

If … Else…Endif

Loop

EOF( )

Do case, Endcase, Otherwise

We will now consider the general forms of these commands.

23.4.1 DO WHILE COMMAND

This command is used when a particular segment of commands have to be executed repeatedly. Thus

it is a looping command that sustains operation while some condition is true. The loop command is

used to return control directly back to the DO WHILE command. The first line of the DO WHILE

statements has the form:

DO WHILE logical expression

Continuous operation is sustained as long as the expression is true, or until an ENDDO or EXIT

command is encountered. The complete DO WHILE statement has the form:

DO WHILE expression

(Command lines)

ENDDO

180

Now let us consider an example using the do while command. Suppose you have to fine the sum of

natural numbers 1 to 100. (That is 1+2+3+4+………..+100). In order to do this we take two variables

S and N. S is the sum of the numbers. N stands for natural number which takes value from 1 to 100.

S=0

N=1

DO WHILE N<101

S=S+N

N=N+1

ENDDO

In the above example we assume that S=0 and N=1. Let us interpret the command line N=N+1. This

shows that natural numbers increase by 1 at a time. The command line S=S+N shows the sum of

numbers.

When N=1, obviously the sum of numbers will be S=S+N = 0+1= 1.

When N=2, S= 1+2=3.

When N=3, S=3+3=6

…………

and so on.

Here the role of the DO WHILE command is that, it repeats the summation process till N<101. Every

time a sum is obtained by the statement S=S+N, N takes the next value N=N+1. Thus a loop is

formed. The process is repeated till the expression N<101 is true. The process stops at the ENDDO

command.

23.4.2 EXIT COMMAND

The exit command transfers control from the DO WHILE loop to the command line following the

ENDDO statement, which is always the last line in a DO WHILE statement. Let us consider the

following example:

181

Do while N < 51

S = S + N

If N = 10

Exit

Endif

Enddo

The exit statement completely exits the control from the loop when the value of N = 10 and

immediately it stops execution following the ENDDO statement.

23.4.3 The IF…ELSE…ENDIF Commands

The IF…ELSE…ENDIF clauses allows a program to make decesions while it is running. The IF

command means the same thing that it does in English: IF this is the case THEN do this ELSE do not

instead.

IF <condition>

<commands…>

[ELSE]

<commands…>

ENDIF

Where <condition> is a valid dBASE logical expression, ELSE is an optional branch to alternative

commands, and ENDIF is the command required to close the IF clause. (If you forgot to include the

ENDIF command, dBASE will not give you any error message. Instead, your program will just

behave in a strange and unpredictable manner.)

23.4.4 LOOP COMMAND

When the loop command is executed the control passes back to the command line following the DO

WHILE command. Sometimes it may be required to stop executing some of the statements at the

lower end of the loop body and transfer the control to the beginning of the loop. In that case the loop

statement is used as shown below:

182

Do while logical-expression

………………. (command lines)

………………..

If condition

Loop

Endif

…………….. (command lines)

……………..

Enddo

23.4.5 EOF( ) Command

The EOF statement, which stands for end of file, is used with several commands including DO

WHILE, DO CASE, and IF (We will discuss these commands later). When an end-of-file condition

exists EOF( ) returns a true value. Otherwise it shows a false value. Going to the bottom of a file with

GO BOTTOM does not position the record pointer to the end of the file. Let us consider the following

example

.USE FILENAME

.GO BOTTOM

. ? EOF( )

.F

You can also go to the end of the file with the COUNT command.

23.4.6 DO CASE , ENDCASE, AND OTHERWISE COMMANDS

The DO CASE Command is used when only one option out of several alternatives (That is several

CASEs) is to be selected. The CASE statement is used to check for a specific condition. Each CASE

statement is followed by one or more command lines. If a CASE statement is true, dBASE performs

all commands between that CASE statement and the next CASE statement. If a CASE statement is

false the command lines are ignored and the control passes to the next CASE statement. This process

continues till a true CASE is found or the ENDCASE statement is reached.

DO CASE

CASE X = 1

183

………………

………………. (command lines)

CASE X = 2

………………..

……………….. (command lines)

CASE……….

ENDCASE

Let us consider the following example.

X = 5

DO CASE

CASE X < 10

? "X is less than ten"

CASE X = 5

? "X is equal to five"

ENDCASE

However, the output from this routine is simply X is less than ten. Although it is true that X is equal

to five, the second CASE statement is never evaluated. In a DO CASE clause, only the first

alternative that evaluates to true is processed; all remaining commands and CASE statements up to the

ENDCASE command are ignored completely. In other words, the alternatives in the DO CASE clause

are mutually exclusive.

OTHWERWISE: It is an alternative statement, which is used when none of the CASE statements are

true.

IN-TEXT QUESTIONS 1

1. Give three examples of control commands.

2. What is the usefulness of EXIT command?

3. When do you use the DO CASE command?

23.5 DATA INPUT COMMANDS IN dBASE

Now we will discuss some input commands, which are used to get data into a dBASE program.

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23.5.1 ACCEPT Command

The ACCEPT command presents a prompt on the screen and waits for the user to respond by typing

some text and pressing ENTER key. Whatever you type is stored in a memory variable.

The syntax for the ACCEPT command is:

ACCEPT [<prompt>] TO <memory variable>

Where <prompt> is optional and <memory variable> is the name of the character memory variable

that will store the user's entry.

The data stored in the memory variable can be from 1 to 254 characters in length. If the user presses

the ENTER key without typing any character, the stored memory variable has an ASCII value of zero

and a length of zero.

PROGRAMMING THE PROMPT

The optional prompt can be surrounded by quotation marks, apostrophes, or brackets. The examples

below are equivalent:

ACCEPT "Enter your name" TO Name

ACCEPT 'Enter your name' TO Name

ACCEPT [Enter your name] TO Name

To embed an apostrophe or other character in the prompt, just use different characters for the outside

delimiters:

ACCEPT "What's your name" TO Name

The prompt itself can be stored in a memory variable.

Characteristics of ACCEPT Command

1. Any data entered via the ACCEPT command can be used for macro substitution.

2. ACCEPT will work with character strings of any length up to 254 characters.

3. To restrict the size of the memory variable character string, use the @….READ command.

4. To convert the character data entered via the ACCEPT command to numeric or date data, use the

VAL or CTOD functions.

23.5.2 INPUT COMMANDS

INPUT command is usually used to enter numeric data from the user. The optional prompt can be

enclosed in double quotation marks, apostrophes, or brackets.

The syntax for the INPUT command is:

INPUT [< prompt >] TO < memory variable >

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Where <prompt> is an optional character string enclosed in double or single quotation marks or

brackets and <memory variable> is any valid memory variable name.

INPUT “Enter your age” TO Age

INPUT ‘Enter your age’ TO Age

INPUT [Enter your age] TO Age

INPUT [Enter your age] TO Age

Let us consider another example to get data into the program through INPUT command.

INPUT “Enter value for the principal” TO principal

The computer will display the prompt on the screen and will wait until you enter the value for the

principal variable.

23.5.3 WAIT COMMAND

The WAIT command suspends processing of a program and waits for the user to press any key. It

accepts only a single keystroke and does not require the ENTER key to be pressed.

23. 5.4 @ ROW, COLUMN COMMAND

The symbol @ followed by row and column position used to position text at a specific row and

column location on the screen. The row-column notation starts at 0,0 which is the first row and first

column on the screen. Therefore, rows are 0-24 for a 25 line screen and columns are 0-79 for a 80

column screen. You can think of @ row,col as ‘at row number, column number’. The SAY and GET

statements are used individually or in combination with @ row,col. Let us consider the following

example:

1 @ 7,10 SAY “What is your name?”

2 @ 7,40 GET name

3 @11,10 SAY “PIN number?”

4 @11,40 GET PIN number

5 READ

In this example, line 1 displays the question “What is your name?’ at row 7, column 10 on the screen.

Line 2 allows data entry from the keyboard into name field of the database in use. Line 3 and line 4

are similar to lines 1 and 2. Line 5 contains READ command which reads your typed response to the

GET statement into the specified field of the database in use.

23.6 OUTPUT COMMANDS

These are some of the important commands used in dBASE in the programming mode in addition to

all dot prompt commands we have used earlier. Examples are APPEND, BROWSE, EDIT, LIST, etc.

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23.7 dBASE COMMANDS AND FUNCTIONS

Several different types of files are created and used by dBASE III Plus. Let us discuss some important

files and their extensions. They are:

Backup files .BAK

Catalog files .CAT

dBASE configuration file CONFIG.DB

System configuration file CONFIG.SYS

Database files .DBF

Database memo field file .FRM

Report form files .FRM

Label form files .LBL

Memory variable files .MEM

Database index files .NDX

Command files .PRG

Query files .QRY

Screen files .SCR

Standard data (or text) files .TXT

View files .VUE

When the files are created by dBASE, they are assigned different three-character extensions, like

CUSTOMER.DBF. Other files, like text files and report form files are created by dBASE. We give a

description for each file type listed above.

1. Backup (.BAK): Backup files are automatically created as a safety measure when an edited

version of a text file is saved. For example, if you use the MODIFY COMMAND FILENAME

statement to change a file, the previous version of the modified file is kept with a .BAK extension.

This happens when you press CTRL-W to save (write) your modified version.

2. Catalog (.CAT): A catalog of filenames, including databases, index Files, etc. is created as files

are created or put into use. The catalog file is established with SET CATALOG TO filename

before file creation activity is started.

3. dBASE Config (CONFIG.DB): This file is used by dBASE when it is started. It contains one or

more commands that control dBASE operation. Normal defaults, including function key values

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and SET functions, are controlled by this file. It can also contain a command line that causes

automatic execution of a command file.

4. System Config (CONFIG.SYS): This file is used by DOS when you turn on your computer. It lets

you have 20 files open at the same time, including 15 within dBASE III applications. It also

creates 15 buffers, which speeds up dBASE III operation by letting it work in memory buffers

rather than having to read and write information to your disk during sorting and listing.

5. Database (.DBF): A standard database file is created and saved using te CREATE command.

6. Memo file (.DBT): When a database file contains memo (text) fields, an auxiliary file having the

extension .DBT is created to contain the memo fields . Databases can contain as many as 128

memo fields. Each memo field can contain up to 5,000 characters. Although memo fields use a

minimum of 512 bytes in the .DBT file, they only occupy 10 bytes in a database file. Memo files

are accessed when a database is being edited with APPEND, BROWSE, CHANGE, or EDIT by

pressing Ctrl-Home at the begining typing text into a memo field, press Ctrl-End to return to the

data entry mask.

7. Report form (.FRM): The CREATE/MODIFY REPORT command helps you to create and save

report format files that control the display and printing of data. The REPORT commands are

described in lesson 22.

8. Label from (.LBL): The CREATE/MODIFY LABEL command helps you create and save label

formats files that control the display and printing of data.

9. Memory Varible (.MEM ) Memory files are created when memory variables are written to disk

using the SAVE command. The resulting file has the extension .MEM which allows you to save

memory variables to disk, and then clear memory to make room for more memory variables.

10. Index (.NDX) An index file is created from an existing database file. The records within an index

file are sorted (rearranged alphabetically or numerically) on one or more specified fields, which

are refereed to as "key" fields. Records retain their original record number. Changes to the

contents of index files change the database file.

11. Procedure (or command file) (.PRG) A procedure or command file is created and saved using

the dBASE full-screen editor or some other text editor; These are pure ASCII files and are

transferable (transportable) between different computer and operating systems. Command files

are created by the dBASE MODIFY COMMAND.

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12. Query (.QRY): A query file establishes a filter that restricts display to specific records that meet

some established condition. The CREATE/MODIFY QUERY command is used.

13. Screen (.SCR): A screen file is used to create or edit screen format files. The CREATE/MODIFY

SCREEN command is used.

14. Standard Data (.TXT): A standard data or text file is created by copying a database file with

COPY TO filename SDF or DELIMITED. .TXT file is created when information is displayed

when the SET ALTERNATE TO filename and SET ALTERNATE ON commands are in effect.

The resulting file may be used by other programs, such as WordStar’s Mail Merge.

15. View (.VUE): Contains the name of related database files and related index and format files,

which list selected field names and relations. Used to call all related files with a single command.

The CREATE/MODIFY VIEW command is used for this purpose.

IN-TEXT QUESTIONS 2

1. What is the difference between INPUT and ACCEPT commands.

2. Give the extension of the following database files:

Program File

Memo File

View File

Back up File


In this lesson we discussed the need for programming in dBASE. In this context we discussed three

types of programming commands. These are control commands, input commands and output

commands. The important commands available and their syntax for use in practice are discussed. We

have provided examples so that you can develop programs in dBASE yourself.


1. Write a program for simple and compound interest using DO-WHILE command.

2. Write a program for finding the sum of natural numbers between 1 to 10.

3. Write a program for printing Pay -slips using INPUT and ACCEPT commands.

4. Write a program for finding prime numbers between 1 to 100.

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IN-TEXT QUESTIONS 1

1. Do While, Exit, If … Else…Endif

2. The exit command transfers control from the DO WHILE loop to the command line.

3. The DO CASE Command is used when only one option out of several alternatives (That is several

CASEs) is to be selected.

.

IN-TEXT QUESTIONS 2

1. INPUT command is usually used to enter numeric string whereas ACCEPT command is used in

character string.

2. .PRG

.MEM

.VUE

.BAK

Disk Operating System (DOS)

5.1 INTRODUCTION

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When the computer starts, it starts the operating system that takes the control of the machine. An

Operating System is a set of programs that help in controlling and managing the Hardware and the

Software resources of a computer system. A good operating system should have the following

features;

1. Help in the loading of programs and data from external sources into the internal memory before

they are executed.

2. Help programs to perform input/output operations, such as;

Print or display the result of a program on the printer or the screen.

Store the output data or programs written on the computer in storage device.

Communicate the message from the system to the user through the VDU.

Accept input from the user through the keyboard or mouse.

5.2 OBJECTIVES

At the end of this lesson, you would be able to;

explain the concept operating system

discuss the functions of operating system

understand the procedures of loading operating system into the memory

use file management features of operating system

create separate locations for logically related files

copy files from one computer to another

use Windows for File Management

5.3 DISK OPERATING SYSTEM

As the name suggests, the operating System is used for operating the system or the computer. It is a

set of computer programs and also known as DOS (Disk Operating System). The main functions of

DOS are to manage disk files, allocate system resources according to the requirement. DOS provides

features essential to control hardware devices such as Keyboard, Screen, Disk Devices, Printers,

Modems and programs.

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Basically, DOS is the medium through which the user and external devices attached to the system

communicate with the system. DOS translate the command issued by the user in the format that is

understandable by the computer and instruct computer to work accordingly. It also translates the result

and any error message in the format for the user to understand.

(a) Loading of DOS

The BOOT Record into the computer memory loads DOS. BOOT Record in turn is triggered by ROM

program already there in the computer.

The system start-up routine of ROM runs a reliability test called Power On Self Test (POST) which

initializes the chips and the standard equipment attached to the PC, and check whether peripherals

connected to the computer are working or not. Then it tests the RAM memory. Once this process is

over, the ROM bootstrap loader attempts to read the Boot record and if successful, passes the control

on to it. The instructions/programs in the boot record then load the rest of the program. After the

ROM boot strap loader turns the control over to boot record, the boot tries to load the DOS into

the memory by reading the two hidden files IBMBIO.COM and IBMDOS.COM. If these two are

found, they are loaded along with the DOS command interpreter COMMAND.COM.

COMMAND.COM contains routines that interpret what is typed in through the keyboard in the DOS

command mode. By comparing the input with the list of command, it acts by executing the required

routines/commands or by searching for the required routine utility and loads it into the memory.

5.4 COMPUTER FILES IN DOS

A file may contain a program or any other kind of information. Generally, a file must be given a

name that can be used to identify it. DOS permits the user to assign a name consisting of two parts

to a file - primary and secondary names. Primary name can be of a maximum of eight characters

consisting of Characters, Alphabets, Number and Hyphen), and the Secondary name should

consist of three characters, which is optional. The primary name and the secondary (or extension)

name, if any, are to be separated by a dot (.).

Primary name can be linked to proper name, whereas extensions are like surnames of people. Using

an extension with the file name is preferable, though optional. However, once the extension is

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specified, using the complete name (primary name and extension, with the period separating them can

only refer the file). Using extensions can be an excellent way of naming a file so that it can be

identified easily.

Examples:

Filename Primary Name Separator Secondary Name

Employee Employee

Employee.Exe Employee . Exe

Employee.Dbf Employee . Dbf

DOS has a way of showing which disk drive is currently active. The floppy disk drives are assigned

alphabets A and B, whereas the hard disk drive is assigned the alphabet C. If your PC has a single

floppy drive, the drive would be A and if it has two, they would be termed as A and B. If your PC

includes a hard disk, besides a FDD (Floppy Disk Drive), the drive names would be A and C. If

the prompt is A, then it implies that the first floppy disk drive is active. Where as the DOS prompt

would be C, if the hard disk is active. Data as well as instructions reside in a file stored in a disk.

5.5 DIRECTORY STRUCTURE IN DOS

The files in the computer come from various sources. Some files come with DOS, while other come

with publications such as a word processor. These files contain codes and other information that is

necessary to make the computer application operational. Before long, there will be hundreds or

even thousands of files in the computer, which can make it difficult to locate specific files.

The names of all the files created in a disk are stored in its directory. Directory is just like a file

folder, which contain all the logically related files. DOS files are organized in a hierarchical or an

inverted tree-like structure. The general analogy is with a file cabinet containing a number of drawers,

which in turn may contain folders. The content of these folders is the needed information.

The file cabinet here is the ROOT DIRECTORY, the drawer is INDIVIDUAL DIRECTORY, the

folders are SUBDIRECTORY and the information in these folders may in turn be classified as

FILES.

Otherwise, the large number of files that get created for various purposes in a disk can make the

directory huge and difficult to view and manage. Therefore, DOS enables the user to organize the

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files in a disk into directories and sub-directories in a hierarchical structure. Directories can contain

other directories. A directory within another directory is called a sub-directory.

Of course, there may be sub-directories of sub-directories, but a file name is the furthest you may

descend down the (inverted) tree of directories and files. Thus, a file name corresponds to a tree

leaf, a sub-directory to a branch, the directory to the trunk, and the root directory to the root of the

tree, hence the name ROOT DIRECTORY.

Sample of Directory Structure

ROOT

Command.com (Personal) Autoexec.bat (Accounts) Pk.bat

LEAVE INSURANCE GPF PENSION LOAN

The directory/sub-directory is represented in bold letters.

5.6 DIRECTORY COMMAND

The content of each of the sub-directory cannot be viewed unless it is made active, or a sub-directory

is specified as part of the DIR command. Doing either of these requires an understanding of the

concepts of navigating around the disk.

The directory, the user is in at any point of time, is called the

WORKING/PRESENT/CURRENT directory. DOS indicates which directory you are in by displaying

the directory's name in the command prompt. For example, the following command prompt indicate

that you are in the DOS directory: C:\DOS>. Knowing which directory is current helps you find

files, and to move from one directory to another more easily. Typically, the ROOT DIRECTORY

(\) is the initial working directory. The entire specification of directory from root is called a PATH.

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By itself, the DIR command is applicable to the working/present directory. The names of the sub-

directories at adjacent levels are separated by backslash (\), while specifying the path to be followed

while traveling to a sub-directory.

5.7 USING PATH TO SPECIFY THE LOCATION OF FILES

A path is the route that leads from the root directory of a drive to the file you want to use.

For example, to access the NOS.LET file in the LETTER subdirectory of NOS directory, DOS must

go from the ROOT (\) directory through the NOS directory to the LETTER directory, as shown in

the following figure:

C:\

NOS

ACCOUNT

SALARY

LETTER

NOS.LET

PROJECT

To specify the same path at the command prompt, you would type it as shown in the following

illustration:

C:\NOS\LETTER\NOS.LET

This is the path or route to the file NOS.LET. The first letter and the colon (C:) represent the drive the

file is on. The first back slash (\) represents the root directory. The second backslash separates the

NOS directory from the LETTER sub-directory. The third backslash separates the LETTER sub-

directories from the file name, NOS.LET.

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Note: MS-DOS recognizes path up to 67 characters long (including the

Drive letter, colon, and backslash).

5.8 DIR COMMAND

The DIR command gives the list of is there on the disk that is mounted on the active drive.

Syntax : C:\> DIR A:\> DIR

Example

A:\> DIR

Volume in drive A has no label

Directory of A:\

COMMAND COM 23612 10-20-88 11.30a

DISKCOPY COM 4235 10-20-88 12.00p

FORMAT COM 15780 03-12-89 12.00p

3 file(s) 325013 bytes free

A:\>

As can be seen, on typing DIR followed by <Enter> key at DOS prompt, five columns of data

followed by the number of files and bytes that are free in the disk are displayed. The first column

contains the primary name of each file resident on the disk. However, most files are named with an

extension, which appear in the second column. Whereas, the third column contains the size of the file

in bytes, and the fourth and fifth columns show the date and time on which the files was created or

last modified. The last line displays the number of file(s) and remaining disk space free in bytes. It

is important to note that the DIR command only displays the names of the files and not their

contents.

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5.9 CHANGING A DIRECTORY

All the names displayed using DIR command that have <DIR> besides them are directories. You

can see the list of files in another directory by changing to that directory and then using the DIR

command again.

The Change Directory (CHDIR) or CD command enables the user to travel around the directories

in a disk. Type the CD command at the command prompt.

Syntax:

A:\> CHDIR {path} or a:\> CD {path}

Examples : (Refer to the figure)

# 1. A:\>CD \NOS

This command makes the NOS sub-directory under the root directory (\) active.

# 2. A:\>CD \NOS\LETTERS

The backslash indicates the root, and LETTERS, which is a sub-directory under the NOS directory,

becomes the working directory.

# 3. A:\> CD \

The root directory becomes the working directory; i.e. you will change back to the root or main

directory. The slash typed in this command is a backslash (\). No matter which directory you are in,

this command always returns you to the root directory of a drive. The root directory does not have a

name, it is simply referred to by a backslash (\).

5.10 MAKING OR CREATING DIRECTORY

As the number of files increases in a disk, a need is felt to organize them in a meaningful way by

creating sub-directories to store a group of logically related/similar files.

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To create a directory, DOS provides the MKDIR (Make Directory) or MD command.

Syntax:

A:\>MKDIR [drive:] {pathname} or A:\>MD [drive:] {pathname}

Square brackets indicate that [drive:] entry is optional.

The MD or MKDIR command creates a new empty directory whose name is the last item specified

in the pathname, in the specified drive. If active, the drive need not be specified. If the directory is

to be created as a sub-directory of the working directory on the active drive, typing MD {directory

name} at the DOS prompt or command prompt is sufficient.

Examples:

# 1. A:\> MD \ACCT\SALARY

makes a SALARY directory in the: drive, under ACCT directory.

# 2. A:\> MD C:\> SALARY

Makes a salary directory in the C: drive, under root directory.

5.11 DELETING A DIRECTORY

You may want to delete or remove a directory to simplify your directory structure. DOS provides

RD (Remove Directory) to delete a directory.

Example:

# 1. A:\> RD \ACCT\SALARY

removes the SALARY sub-directory in ACCT directory.

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NOTE: You cannot delete a directory if you are in it. Before you can delete a directory, you must

type cd.. at the command prompt. At the same point of time, the directory to be deleted should be

empty.

5.12 COPYING FILES

To copy a file, DOS provides `COPY' command. When you use `copy' command, you must use the

following two parameters; the location and the name of the file you want to copy, or the source;

and the location and the file name to which you want to copy the file or the target (destination).

You separate the source and the destination or target with a space. The syntax of the `COPY'

command is

COPY {source} {destination} or,

COPY [drive:] [path] [filename] [drive:] [path] [filename]

i.e. the first set of drive, path and filename refers to the source file, and the second set of drive,

path and filename

refers to the destination file.

(a) Copying Single File

To copy the DEBUG.EXE file from the DOS directory to the NOS

directory

1. Return to the root directory by typing the following command prompt: CD\

2. Change to the DOS directory by typing the following commands at the DOS prompt: CD DOS

3. To copy the file DEBUG.EXE file from the DOS directory to the

NOS, directory type the following at the command prompt:

Copy c:\dos\debug.exe c:\nos

and the following message appears: 1 file (s) copied

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Examples:

# 1. A:\> copy a:\letter\office.doc \letter\office.bak

makes a copy of the office.doc file in the current or working directory with a new name office.bak

# 2. A:\> copy office.doc a:\letters\nos.mem

copy the file office.doc from the root directory to the sub-directory LETTER under root directory with

a new name nos.mem.

If the target drive is not specified, the copied file will reside in the disk mounted on the active drive.

5.13 USE OF WILDCARD CHARACTERS

If you want to carry out a task for a group of files whose names have something in common, you can

use wildcard characters to specify groups of files. DOS recognize two wildcard characters: asterisk

(*) represents one or more characters that a group of files has in common; and the question mark

(?) represents a single character that a group of files has in common. You can use wildcards to

replace all or part of a file's name or its extension. The following table shows examples of wildcards:

Wildcard What it Represents Example

*.TXT All files with a .TXT extension JULY.TXT

LETTER.TXT

REPORT.* All files named REPORT with any REPORT.TXT

extension REPORT.LET

REPORT.WRI

M*.* All files beginning with letter M MEMO.TXT

regardless of their extension MARCH.XLI

???.* All files having 3 letter names, SUN.BMP

with any or no extension WIN.LET

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You can include the wildcard in the command.

Use of wildcard characters in COPY command

# 1. A:\>COPY \letters\*.COB B:

It means, copy all files with extension *.COB from the directory LETTERS under the ROOT

directory to the working or ROOT directory of the `B' drive.

# 2. A:\> COPY B:\COMPANY\OPEL.*

The command is to copy all files with primary name OPEL (irrespective extension) in the directory

COMPANY under ROOT of the drive `B' into the current working directory of the disk mounted in

À' drive. Incase of one drive, the system will ask for the source and

target drive.

The command,

#3.A:\>COPY C:\*.*

copies all files of the ROOT directory of the 'C' drive into the working directory of the 'A' drive.

# 4. A:\> COPY LETTE?.* B:

copies all files with primary name consisting of 6 characters in total and LETTE as the first five

characters (irrespective of extension name) into drive `B'.

# 5. A:\> COPY B:\?.DOC

copies all files having a primary name of one character with an extension .DOC from ROOT

directory of 'B' to the ROOT directory of À' drive.

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5.14 RENAMING FILES

To rename a file, DOS provides REN command. The REN command stands for "Rename".

When you use the REN command, you must include two parameters. The first is the file you want to

rename, and the second is the new name for the file. You separate the two names with a space. The

REN command follows this pattern:

REN oldname newname

Example: REN NOS.DOC NOS.MEM

Rename the old filename NOS.DOC to a new filename NOS.MEM.

5.15 DELETING FILES

This section explains how to delete or remove a file that is no longer required in the disk. DOS

provides DEL command, which means to delete.

Syntax : DEL {drive:} {path} {filename}

Example:

# 1. DEL \DOS\EDIT.HLP

delete the EDIT.HLP from the DOS directory under ROOT directory.

5.16 PRINTING A FILE

The `PRINT' command of DOS works more or less like `TYPE' com

mand, but at the same time, it enables the content of a text file

to be printed on a paper.

Syntax:

A:\> PRINT [drive:] {path} {filename}

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Example:

A:\> PRINT \AIAET\LETTER\AIAET.LET

IN-TEXT QUESTIONS 5.1

1. The startup routine runs, when machine boots up is known as

a) POST

b) BOOT up

c) Operating Routine

d) I/O operation

2. Operating system is also known as:

(a) database

(b) system software

(c) hardware

(d) printer

3. What is the maximum length allowed for primary name of a computer file under DOS?

(a) 8

(b) 12

(c) 3

(d) None of the above

4. Which of the following could be a valid DOS file specification?

(a) NOSFILE.POST

(b) NOSFILE.P.OST

(c) NOSFILE.DOC

(d) NOST.FILEDOC

5. How many characters form a secondary name for a file?

(a) 8

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(b) 12

(c) 3


6. What is the name given to something that the computer will automatically use unless you tell it

otherwise?

(a) a specification

(b) a wildcard

(c) a default

(d) a rule

7. As per symbolic notation of DOS, which of the following indicates the ROOT directory

(a)*

(b) >

(c) /


8. In wildcard specification `?' is used as replacement for

(a) one character

(b) two character

(c) three character

(d) none of the above

9. With DOS, you may use the `*' and `?':

(a) when changing the default settings

(b) to represent unspecified characters in a filename

(c) instead of wildcard characters

(d) in the extension but not in the drive name or the file name

10. DOS system file consists of

(a) IBMBIO.COM, IBMDOS.COM, COMMAND.COM

(b) COMMAND.COM, IBMBIO.COM, FORMAT.COM

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(c) SYS.COM,IBMBIO.COM,IBMDOS.COM


11. The batch file uses the extension

a) .BAT

b) .DOC

c) .PRG

d) .DOS

12. To display the list of all the file of the disk you would type

(a) DIR

(b) COPY

(c) DIR FILES

(d) DIR AUTOEXEC.BAT

13. State whether the following questions are True(T) or False(F).

(a) Command.Com is hidden file.

(b) Primary name of a file can be of 10 characters.

(c) The command MKDIR and MD performs the same task.

(d) Under DOS .EXE is not an executable file.

(e) DIR command is used to see the content of a specific file.


In this lesson you were introduced to one of the most popular desktop operating system and its

working environment. It explained the directory structure, file naming conventions. It also talked in

great length about the file management in terms of COPY, DEL, and MOVE. Here you learned the

steps involved in loading of operating systems into computer.


1. Explain in brief what do you understand by Operating system.

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2. Explain the process involved in loading of Operating System.


1. 2.b3.a,4.b,5.b,6.c,7.d,8.a,9.b,10.a,11.a,12.a,13. F,F,T,F,F

INTRODUCTION TO WINDOWS 3.1

6.1 INTRODUCTION

If somebody buys a new computer today, it will probably come loaded with Windows. It is a

Graphical User Interface (GUI) program meant for IBM compatible PCs. It provides the flexibility of

using graphical icons and work interactively with the computer. One doesn't need to remember

operating system commands and type them. He just has to move the small mouse arrow key, known

as mouse pointer around the screen (better known as window) and select the require command by

pressing the click button. Each window, which represents programs, can be resized and moved around

the screen. Multiple windows can appear on the screen at the same time giving user the flexibility of

operating more than one

Program.

6.2 OBJECTIVES


understand the concept of windows working environment

differentiate between confessional character display interface and graphical user interface.

explain about various features of Windows

understand various Icons and their functions.

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6.3 TYPES OF WINDOWS AND ICONS

Before using Windows effectively, it is very essential to understand the concept of window type and

Icons used in Windows. The entire screen is termed as Windows Desktop, on which all windows are

displayed. It is same as that of laying all your work on the surface of your working table. Here the

working table is the Windows Desktop and all your work is individual windows on the desktop.

In general, there are two types of windows and three types of Icons which window uses. The window

types are

1. Application windows, which displays the executable windows program in GUI mode. These

windows can be, opened, closed, resized and moved around the screen or the desktop.

2. The other type of windows is a document window, which are generated by the executable or

application program. These document windows cannot be sized or moved outside the limit of its

parent application windows.

Windows uses three types of icons, namely application, document and program icons.

1. Application icons are the minimized version of the currently running application program. This

icon appears at the bottom of the desktop and can be maximized.

2. Document icons are the reduced document windows. When maximized, it appears within an

application window's workspace.

3. Program icons that appear within Program Manager and clicking on these icons activate the

associated applications and also load the related documents or files.

6.4 PARTS OF WINDOWS

All most all windows have common components. The components are;

1. Title Bar

2. Buttons for Minimize, Maximize and Restore

3. Borders for Resizing

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Minimise and Maximise Button

4. Menu bar and Pull-down menus

5. The scroll bar

(a) Title bar

Title bar is displayed in color at the top of the windows. It contains the name, or the title of the current

windows. The windows can be moved around the window desktop using this title bar.

(b) Buttons for Minimise, Maximise and Restore

These buttons are displayed at the top-right corner of the screen. As the name suggests, minimise

button is used to reduce the current windows into an applications icon, which will appear at the

bottom of the windows desktop.

Similarly, maximise button is used to expand the current windows to take up the entire desktop.

Restore button is used to restore the state of the windows, where it was before maximization.

(c) Borders for Resizing

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Title Bar

ControlButton

Menu Bar

Status Bar

Scroll BarResizing Bar

A thin border appears around the windows, which can be used to resize the current windows. To

resize the current windows, just place the pointer on the border (this will become two-headed arrow

) of the windows, click the mouse button, hold and drag to the desired location. The windows will

change its size. Vertical and Horizontal borders can be used to change the width and height of the

windows respectively, while corner border can be used to change width and height simultaneously.

(d) Menu bar and Pull-down menus

Menu bar is located under the Title bar and contains the related Pull-down menus for the currently

active windows. Clicking on a menu name will activate a pull-down menu with various options to

select.

(e) The scroll bar

When the active windows cannot accommodate the data to be displayed then it provides a scroll bar

that helps to move through the data. Vertical scroll bar allows to view data by moving up or down

through a document, whereas horizontal bar allows the movement from left to right. The vertical

scroll bar appears on the right side of the active windows and horizontal scroll bar at the bottom.

6.5 WINDOWS DIALOG BOXES

While using application program in window, sometimes it is require to change the settings within a

program for example default margin the a word processing document, default printer, font type and

size etc. All these are accomplish by window's dialog box, which appear when the menu with an

ellipsis (..) beside it is activated. It is basically serve two purposes one that it allows to change/rest

the parameters related to currently running application and displays information such as warnings,

error message etc. The displayed dialog box may contain the followings;

(a) Command Button

This button activates an action. The most commonly used command buttons are OK and CANCEL.

Command buttons with an ellipse (..) indicate a link to another dialog box.

(b) Check Box

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Check box allows selecting one or more option from a list of options. When selected an X appears

besides the option selected and the corresponding option becomes active.

(c) List Box

List box displays a series of options available in a column. To select an item, move the mouse pointer

to the item and click on it. If the number of items is more than the height of the list box, then it

provides a scroll bar to move through the entire range of items in the list box.

(d) Option Buttons

It has the same features as that of check box. It allows selecting an option in a list of choices. When

selected, the small hollow circle gets filled. Once an option gets selected from the available set of

options, other options automatically get deselected.

6.6 DISK SPACE REQUIRED

Ms-Windows along with MS-DOS version 6.0 requires a minimum of 15.8 MB and maximum of 18.3

MB of free disk space. Minimum disk space assumes no optional components, network or printer

settings. However maximum disk space includes all installable components, network and printer.

6.7 WINDOWS VS. MS-DOS

Windows provides tools to accomplish all the tasks in case of file and directory management as in

MS-DOS. The main difference is how the work is done. Rather than remembering all the commands

and typing them at the DOS prompt, in Windows one can move the mouse pointer to the required

command, and windows will execute the command. Windows supports all the File and Directory

management commands of MS-DOS and it also supports Ms-DOS conventions in working with files

such as wild card characters.

6.8 WINDOWS PROGRAMS

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In this section, programs provided in windows such as program Manager, File manager etc. are

discussed. These are vital part of windows operating environment and one must know how to work

and use these programs.

(a) Program Manager

When window program starts Program manager is the first windows displayed on the window

desktop. The only way to leave windows is to closing or exiting this program manager. Within

Program Manager there is some secondary window known as group windows, which appears as fully

opened window such one with title 'Main' or as group icons, which appears at the bottom of 'Main'

windows. A group icon is a group window, which can be minimized. Group windows contains

logically related programs, such as one group windows can contain all programs associated with

database while another may be for word processing.

There are five default groups in Windows. They are;

Main group of windows contain all the system applications: File manager, Print Manager, MS-DOS

prompt, Windows Setup and PIF Editor.

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Applications group consists of all the application found on your hard disk, while installing the

windows. How ever if, during installation process if you chose the Custom Setup option and chose not

to have Windows set up applications from your hard disk, the program manager will not contain an

Application group.

Accessories group is made of windows based applications for word processing (Write), drawing

(Paint), communications (Terminal), plus several other useful applications.

Games group contains windows based games.

StartUp group has application that loaded when windows system starts initially. Any applications

can be added to this group. This group remains empty until, an application is added to it.

Windows provide the flexibility to install other group windows also.

Group windows can be resized, moved and it contains the icons for the program, which can be

executed. Program items can be added deleted in-group windows and they can be copied between

group windows also.

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However neither the group windows can be moved outside the program manager nor the group icons.

By selecting the icons, one can run the associated program files. All the program items can be moved

between groups copied or renamed.

(b) File Manager

As the name suggests, File manager is used to manage or manipulate both disk and the disk files. It

provides visual representations of all disks and disk files in the system.

As displayed in the above figure, the directory structure for the hard disk of the system and all the

files in the current directory, appear in a document windows, known as directory window. The

attributes of one or more file can be changed, by selecting them from the directory window. They can

also be moved between directories, or opened, renamed, printed, deleted or copied.

(i) Selecting File(s) and directories

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Window TitleWindow Menu

Directory Icons

File and subdirectory icons of currentdirectory

Drive Icons

Drive label Or Network Drive

File Manager allows you to select one or more than one files at a time for copying, moving or

deleting or to perform other related task.

To select a file or directory clicks the desired icon. Or press the TAB button to move to the list of

files, and then use the direction keys or arrow keys to select.

To select consecutive files, select the first file, press and hold down the SHIFT key, and then click

the last file on the desired file list or group. Alternatively, select the first file, press and hold down

the SHIFT key and then use arrow keys to extend the selection to the last item in the group.

To select or cancel selection of the non-consecutive files, press and hold CTRL key and click on

each file. Alternatively, press SHIFT and F8 key, use arrow keys to move to each file, use

SPACEBAR to select the file or to cancel already the selected file, then press SHIFT and F8

again.

To select similar type of file, activate the Select Files option from the File menu bar. In the text

box of the dialog box specify the type of files to be selected. For example *.DOC to select all files

in the current directory that has .DOC as extension or secondary name.

IN-TEXT QUESTION 6.1

1. State True or False.

a. File Manager is used to start Windows.

b. Group windows and group icon can be moved out of Program Manager

c. File maintenance is done using File manager in windows.

d. To activate a program when windows starts, you need to add it to File manager.

e. Print manager and File Manager are available in Games windows.


In this lesson you were introduced to the concept of windows working environment and graphical user

interface. It also discussed various features and components of windows. It explained with examples

the icons and their functions. This also discussed how to select files and directories.

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1. Briefly discuss why Windows is popular.

2. Briefly explain about different components of windows and how to start windows.

3. How a group icon is different from individual program icon?

4. Which group programs are loaded when windows starts-up?

5. Can a DOS based application be used in Windows?


1. (a) False (b) False (c) True (d) False (e) False

FILE HANDLING IN WINDOWS 3.1

7.1 INTRODUCTION

Windows being a GUI, gives better flexibility and easier to use for file management. Using the File

Manager feature of Windows, one can easily copies, move, delete, rename files and also create and

remove directory. This avoids the painful task of remembering all the file management DOS

commands.

Windows can run two types of applications, standard DOS based applications and Windows based

applications. DOS based applications are standard DOS programs such as WordStar, dBase etc.

developed to run in DOS environment, and not specifically meant for windows. Whereas a windows

application is specifically developed to run under Windows environment which support GUI.

7.2 OBJECTIVES


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appreciate the GUI feature of windows

understand the file and directory handling in windows

use file manager for file handling in windows

sort file using file size, name, type

search and locate file(s)

do file copy, move from floppy disk to hard disk drive and vice versa.

7.3 DIRECTORY AND FILE MANAGEMENT IN WINDOWS

Windows provides File manager for manipulating Directory and Files of a system. It is an essential

part of Windows and run like any other windows program. Main program consists the icon for File

Manager. Double clicking on the File Manger icon activates it from the Main program group. Other

way of activating it is to highlight the File Manager icon and hit the Return key

File Manager can be closed like any other windows program. File Manager can be minimized while

running some other application and expanded once the execution is over. The total amount of

diskspace, free diskspace available, the size of the selected file is shown for the currently open

directory on the status bar, which appears at the bottom of the File Manager.

(a) Drive Window

Currently selected drive is displayed as another windows within the File Manager window. The

command to resize, move or minimize is same as that of any other window. The only difference is

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that it is divided in two parts; right one displays the directory structure of the currently selected drive

and the left part displays the contents (such as files, sub-directory etc.) of the currently selected

directory.

(b) Directory Operations

File Manager provides the features to manage all the drives in your system and/or

connected to your system through network. It allows to copy, move or delete files

within a drive, between drives of the system and systems connected

through network. Once the drive is changed, directory and files under the

newly selected drive will be displayed in the current directory window.

(c) Changing Disk Drives

To change drive, click on the desired drive icon or press <CTRL> and the designated drive letter such

as C, D E etc. Other way of selecting a drive is to click on the Disk option of the File Manager menu

bar, and select the desired drive letter.

(d) Creating a New Directory

A new directory or sub-directory under an already existing directory can be created using File

Manager. First click on the File menu option of the File Manager. This will bring up the pull down

menu having Create Directory. Selecting this option will activate the Create

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Drive window

Left Pane of window drive

Right Pane of window drive

Directory dialog box with current directory path. To create a sub

directory under the current directory, type down the new sub-directory name in the text box. To create

a sub-directory under some other directory, type the entire path in the name text box. To finish the

entry and create the new sub-directory, click on the OK button.

(e) Changing Directory

To go to the desired directory under the currently selected drive, double click on the directory name.

This will make the selected directory as the currently active directory and all the sub-directory and

files under this directory will be displayed at the right pane of the document window.

File manager has the flexibility of displaying different groups of files in the currently selected

directory. Click on the View option of the File Manager menu bar, which will activate the pull-down

menu with option 'By File Type'. Selecting this will bring up the 'By File Type' dialog box. Use the

wild card characters to enter inn the name text box, the desired file type you want to see.

In File Manager, it can also be specified what all information for files can be displayed. In addition to

the File name, File path one can display file size, date and time it was created/or last modified etc. To

display all file information, select the VIEW option on the File Manager menu bar and activate the

option 'All File Details'.

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In File Manager, sub-directory and file under the currently selected directory are displayed in

alphabetical order. However they can also be displayed in order of file type, date or file size. To

change the displays option, select the VIEW option on the menu bar and selected the desired option.

Available options are;

Sort by Name: Displays all files in alphabetical order of File name.

Sort by Type: Displays all files in alphabetical order of extension

Name

Sort by Date: Displays File in order of creation/last modification

Date.

Sort by Size: Display all files in order of File Size.

7.4 FILE OPERATIONS

File Manager provides tools such as copy, rename, move, rename for management of files within

directory, between directories and also between drives.

(a) Copying a Diskette

Like Diskcopy of DOS, windows also have the tool in File Manager for making copies of disk. The

source disk replaces the content of the target. However the target disk type and size should same as

that of source disk. If an unformatted disk is used in target drive, the target disk is formatted as that of

source disk type and size while copying the files. This copy option is very useful for making back-up

copy.

Insert the source disk into the drive and select the DISK option of the

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File Manager menu bar, and activate the 'Copy Disk'. This will copy the files from the source disk into

the memory. Now select the target drive from the copy dialog box and click on OK button. This will

start the coping process from the source to target disk.

(b) Copying/Moving Directory or Files

In file Manager, one or more files or Directory can be copied or moved into different location using

two different methods; Drag-and-Drop method and Keyboard method.

(i) Drag-and-Drop Method

File Manager has the capabilities of copying or moving files and directories in more interactive and

visual ways as compared to MS-DOS. Open the source directory select the files to be copied and then

drag them in to the desired target directory, another drive icon, another directory window or to a file

list in a different directory window and drop them.

Confirm the copying operation, by clicking on the OK button of the dialog box. This will copy the

selected files in to the target drive. If the file(s) to be copied is/are already presents on the destination

directory or drive, confirm replace message by clicking on the YES button of the dialog box.

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(ii) Using Keyboard

Instead of using mouse for the above operation, one can alternatively use the keyboard to select

COPY and MOVE command. As in the case of drag-and-drop method, the destination can be a

directory window, directory icon or drive icon. Click on the desired file name to be copied or use the

direction key to highlight it. Select the COPY or MOVE option from the File menu bar of File

Manager as per the requirement.

Alternatively press F8 for copy or F7 for MOVE operation to start. As in the case of drag-and-drop

method, COPY or MOVE dialog box appears on the screen. Enter the destination path or drive. If the

destination directory does not exist, it will ask whether to create a new one. To start the operation,

click on the OK button or press Enter key ().

7.5 DELETING FILES AND DIRECTORIES

File Manager provides greater flexibility in deleting files and directories. However in the case of

network drive, one cannot delete files or directories if he has not the privilege or permission of doing

so. File Manager allows to delete an entire directory including all its files and subdirectory in a single

command. However, in DOS, one first need to delete all the files and sub-directory of the desired

directory to be deleted.

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Select the file(s) or directory to be deleted (alternatively use tab to move the cursor to the desired

location and use direction keys to select the files). Activate the Delete option from the File menu bar

of File Manager and the delete dialog box appears on the window desktop. To delete the already

select files or directory, click on the OK button. To delete other files or directory, enter the file name

or path and click on the OK button.

This will activate directory delete dialog box. Click on YES button to confirm the deletion. Click on

Yes to All to delete all selected files or click on Cancel button to cancel the delete operation.

7.6 FILE RENAMING

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File Manager allows changing the name of a file with a restriction that the new file name should

follow the DOS file naming conventions. The new file name should not be more than eight characters

long with an optional three characters extension or secondary name with permissible set of characters.

First select the file to be renamed, and then chose the Rename option from the File menu bar of File

manger. The Rename dialog box appears with name of the currently selected file in the From text box.

Now enter the new name for the file in the To text box and click OK button or press Enter key. This

completes the renaming process.

Note: One can use wild card characters for renaming files.

7.7 SEARCHING FOR FILES AND DIRECTORIES

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File Manager provides the tool to search a file, a group of files or subdirectories. This is particularly

helpful, if you know a particular file is on your disk, but you don't remember where the file exists.

Here you can conduct a search on your disk, directory to locate the file. The result is displayed in

Search Result window, which can be resized, minimized or maximized, closed the same way as other

window.

Click or select the directory to be searched and then choose Search option from the File menu.

Specify the filename, or use wildcard character (such and * or?) in the Search For text box to search

for a group of files or directories that have related file names or extensions. The Search Result

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windows will contain all the files that meet the search criteria. To cancel the search operation, press

ESC key.

7.8 WORKING WITH FLOPPY DISKS

At times one need to copy files onto a floppy as backup or copy file from floppy to hard disk for

further processing of files. File manager provides tools to work with floppy disks.

(a) Formatting a Floppy

Before using a new floppy to receive data, it has to be prepared for that. File Manager format

command allows you to prepare a new/old floppy to receive data. The format command has three

options, which are optional.

Label

As the name suggests, it is a name for the formatted disk to identify it. A label or volume label should

not more than 11 characters long.

System Disk

While formatting a disk, it can be opted to make the disk a system or startup disk. System disk is used

to boot the system from a floppy drive. When opted, all the system files are copied into the specified

area called system area or boot sector of the floppy drive. System disk comes handy, in case the hard

disk is not working or one needs to bypass booting from hard disk for any reason.

Quick Format

This option is available for disk that has already been formatted. When selected, file Manager just

removes all information about directory and files from disk, making it faster as compared to standard

format procedure. However Quick Format does not check the disk for bad sectors.

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To format a disk or floppy using File Manager, insert the disk into the drive and select Format Disk

option from Disk menu bar. From the list of drives, select the appropriate drive letter. All the required

parameters are adjusted according to the selected drive.

Choose the option such as Label, System Disk or Quick Format. In case of Label option, specify the

volume label name for the disk. Complete the other areas of the dialog box and click on OK button.

This completes the entry and File Manager starts formatting the disk according to the specification

given.

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Choose the best answer for each of the following questions.

1. Windows is a

(a) System Software

(b) Database Software

(c) GUI based Software

(d) None of the Above

2. Which are the following types of Icons used by Windows

(a) database, operating system

(b) program, document, application

(c)only program


3. Which of the following on a command button indicates a link to another dialog box

(a)/

(b)*

(c)..


4. File manager is a part of which group of Windows

Program Manager

Main

Application

None of the above

5. Which of the following groups of Windows contain all executable software found on your hard

disk.

(a) Main

(b) Print Manager

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(c)Application


6. Which of the following allows all types of file manipulation such a COPY, MOVE etc.

(a) Print Manager

(b) File Manager

(c) System setup

(e) None of the above


This lesson discussed windows's graphical user interface (GUI) in a great length. In the beginning it

discussed what is directory and file management. Then with examples it explained how to do

directory maintenance in-terms of create, delete and change directory. It also discussed how to sort

files by name, type, size and dates. Here you learned how to file operation in windows using File

manager and what is drag and drop method. At last it explained how to search for file and directory

and how to work using a floppy diskette in windows.



1. (c) 2. (b) 3. (c) 4. (b) 5. (c) 6. (b)

WINDOWS 95- AN INTRODUCTION

8.1 INTRODUCTION

Windows 95 is the upgraded version of Windows 3.x series with lots of new features embedded into

it. It is a complete paradigm shift from windows 3.x working environment.

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It is the entry point to a 32-bit operating/computing environment with less set of hardware

requirements. It has more compatibility with other software as compared to its previous version and

provides easy installation. It also runs most of the Windows 3.x and Ms-DOS programs. Windows 95

also provides flexibility to configure hardware, easy link to a network or setup a network, install and

uninstall programs automatically. It also has lots of other useful features like easy Internet access,

multitasking, and its most useful feature is long file names.

8.2 OBJECTIVES:


understand the difference between Windows 3.11 and Windows95.

able to work on Windows95

appreciate the uses of Long file name

appreciate the new look and feel of Windows95.

8.3 IMPROVED FEATURES OF WINDOWS 95

Graphical User Interface :

As compared to Windows 3.x, Windows 95 provides user-friendlier interface to work on. Its

improved graphical user interface makes learning and using Windows 95 more natural and easier for

all types of users. It is more powerful, customizable and efficient.

Start Button

Introduction of START button in Windows 95 made life much simpler while there is a need to access

multiple programs. It is the gateway of accessing most of the functionality available in the computer

loaded with Windows 95. Just Click on the Start button anytime to start any programs, open or find

documents, change windows settings, get Help, manage Files, maintain system, and much more.

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Taskbar

As the name suggests, the Task bar provides information and access to the entire task that has been

currently activated by Windows 95. Using this one can keep a track of what all programs have been

activated and switched between them.

Windows Explorer

Windows Explorer is more or less acts as a File Manager for Windows 95, but with lots of new

features. It is more efficient, faster and user friendly as compared to File Manager of Windows 3.x.

Using Explorer one can easily browse through all the drives and network resources available and

manage files.

Right Mouse Button

Clicking on the right mouse button activates a pop-up menu in any programs so as to help in

completing a task efficiently.

Long File Names

As the Ms-DOS convention follows, non-of the file used in DOS environment should be more than 8

characters of primary name and optional secondary name (extension) of three characters. However

Windows 95 has broken this barrier. Windows 95 supports long file names, maximum of 255

characters. It also allowed space to be used in between file name. This helps to make files and folders

(directory/subdirectory) easier to organize and find.

Shortcuts

As the name suggests, SHORTCUTS are the shortest way to access programs, files and other

resources in Windows 95. Instead of going through the structural process of accessing a program, one

can create "shortcuts" to access them. It creates links for easy access to files, programs, folders, and

more.

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Multitasking

Multitasking allows the user to activate and accomplish more than one task at a time. For example,

work on a document file in WORD programs, while copying file from other computer available in the

network. With Windows 95, 32-bit computing environment, the user can do more than one task a

time.

Easy Internet Access

One of the most useful and entirely new features is Windows 95 easy access to Internet. It provides

built-in Internet functionality to setup link and access Internet with less amount of Hardware and

Software requirement. It also provides connectivity software from Microsoft Network (MSN),

CompuServe, and America Online.

It also improves the efficiency of working on Internet with applications that support the latest Internet

technologies, such as ActiveX, Java, and streaming audio and video.

Software Compatibility

Windows 95 provides complete backward compatibility. It is easily compatible with applications

developed for MS-DOS and Windows 3.x environment. It also supports the latest 32-bit technology.

Most of the latest software packages are now built on Windows 95 operating environment.

Great Gaming Platform

Windows 95 support rich graphics, high quality audio and video. It also requires all most no editing of

Config.sys files so as to support these technologies. All this is possible because of Windows 95

compatibility with latest and hottest technologies like Plug and Play, AutoPlay, and built-in support

for MIDI and digital and surrounds video.

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Hardware Compatibility

Windows 95 provides greater Hardware compatibility as compare to any other operating environment.

It has flexibility of supporting hardware from different vendors. Its Plug and Play functionality allows

to insert the hardware card into the computer and when the computer is turned on Windows 95

automatically recognizes and sets up the hardware.

Find Utility

Find Utility of Windows 95 allows you to do searches by partial name, last modified date, or full text.

In addition, you can save, rename, or view files from within the result pane, just like you can from

Windows Explorer.

Help

Windows 95 provides online help to accomplish a task. If the user is not sure how to perform a task,

Windows 95 Help will provide structured process how to accomplish the task. Simply right-click on

any object in the user interface (icons) and you'll get relevant descriptions about that object.

(a) System Requirements

CPU Recommended 486/25 MHz-based system or

more

Memory Recommended a minimum of 8-MB memory

(RAM).

Hard Disk SpaceAvailable free hard disk space of 40-45 MB.

Display VGA or higher-resolution display

Operating System MS-DOS

Peripheral/ Miscellaneous Compatible pointing device

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(b) Windows Desktop Icons

Icon Purpose

My Computer Provides direct access to local drives, printers,

Control panel, and the Dial-up Network utility.

Network Neighborhood Access to shared resources on the machine and

computers on local and wide area network.

Recycle Bin Provides drag and drop facilities, deletion of file from

folders in the machine and provides a second chance

to recover files deleted from the hard disk.

Inbox or Microsoft Outlook Universal in-box for all mail sources including faxes,

mail, exchange, and others.

Fig. 8.1

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8.4 START BUTTON AND TASK BAR

Windows now features the Start button and Taskbar at the bottom of the screen. This bar contains the

Start button. Using this button, a program can be quickly started or file can be searched for. Quick

help on how to use windows can also be obtained from this task bar.

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Fig. 8.2

Click on the Start to activate the Pop-up menu so as to open a program, find a file or folders

(directory or sub-directory), and change the settings for Windows95, Run a program or shut down the

computer and also to get help on windows.

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If you have opened more than one program or windows, you can switch between them. All the opened

windows or program appears on the Start or the Task bar as a minimized icons. Click on the desired

icon to open the designated program. Similarly if you don't need a windows too frequently, click on

the minimized button of the windows. This will send the activated window as small icon to the task

bar.

(a) Steps to start a program

1. Click on the Start button, and then point to Programs option.

2. Select the program you want to run. If the program you want is not on the menu, point to the

folder that contains the program.

3. Click on the program icon or menu.

Once the selected program starts, a small icon appears on the taskbar. If you have opened more than

one program, click on the required program icon on the taskbar to make it currently activated

program.

If the desired program is not available on the program menu or one of its submenus, point to Find on

the Start menu, and then click Files Or Folders where the program resides. You can also use the Find

dialog box to locate the program file.

(b) Steps to open a recently used document

1 Click on the Start button

2 Select/point to Documents option.

3. Select the document you want to open, by clicking on it

Note:

All programs are not capable of adding files to Document menu. So if the desired document to be

opened is not listed or available in Document Menu, click on the Start button, and then select the Find

option. Select/Click "Files Or Folders" option, and then use the Find dialog box to locate the file.

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8.5 MY COMPUTER

It allows looking at a glance to all the resource available on the machine such as floppy drive, CD-

ROM drive, Hard Disk etc. If you have network drives mapped as local drives they will also show up

here. Double clicking on a drive in the top level of my computer will open another window containing

the main folders on the select drive. Double clicking on any of the folders in the drive window will

open another window showing the contents of the folder.

Double clicking on either the Control Panel folder or the Printers folders in My Computer windows

will activate the respective windows for Control panel or Printers. Using this you can manipulate the

settings for your Computer or Printer the same way that you were accessing them from the Start

menu.

Fig.8.3

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My Computer is the quickest way of accessing all the resources available on the computer. Even this

can be used to copy, move, delete files among or between floppy and Hard Disk or network drives.

Fig 8.4

My Computer also provides the tools to change the settings of the available resources. Select the

media such as floppy disk, hard disk drive you want to change the settings and right click on it. This

will activate a Pop-Up menu. Now select the Properties option from the pop-up menu. This action will

display the property windows with three options: General, Tools and Sharing. Using these three

options you can change the properties of the selected media.

8.6 WINDOWS EXPLORER

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As the name suggests, Windows Explorer let you explore the contents of your computer and do file

management. It is the improved version of File Manager in Windows 3.1 or 3.11.

Fig. 8. 5

To activate Windows Explorer, Click on the Start Button on the Task Bar and select Programs option.

This will activate another Pop-Up menu. Now select Windows Explorer

Option.

Windows Explorer displays on the left-hand side of the screen, all the folders on your computer in a

hierarchical order. On the right hand side of the screen, it displays all the files and folders in each

selected folder.

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Fig 8.6

Windows Explorer is especially useful for copying and moving files. You can open the folder that

contains the file you want to move or copy, and then drag it to the folder you want to put it in.

(a) Steps to copy a file or folder

1. Go to My Computer or Windows Explorer

2. Select the file you want to copy by clicking on it.

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3. Go to Edit Menu and Select/Click Copy option.

4. Open the folder or disk drive where you want to copy.

5. Again go to Edit Menu and Select/Click Paste option.

(b) Steps to move a file or folder


2. Select the file you want to move by clicking on it.

3. Go to Edit Menu and Select/Click Cut option.

4. Open the folder or disk drive where you want to move.

5. Again go to Edit Menu and Select/Click Paste option.

(c) Steps to delete a file or folder


2. Select the file or folder you want to delete by clicking on it.

3. Go to File Menu and Select/Click Delete option.

Note:

Files or folder deleted are stored in the Recycle Bin until the Recycle Bin is emptied. Files or

folders can also be deleted by dragging file or folder icons onto the Recycle Bin icon. If SHIFT

key is pressed while dragging, the item will be deleted permanently from the computer without

being stored in the Recycle Bin.

To select more than one file or folder to copy, while pressing the CTRL key, click the items you

want to select.

(d) Steps to copy a file to a floppy disk

1. Insert the disk in the floppy disk drive.


3. Select the File you want to Copy, by clicking on the file.

4. Go to File menu, point to "Send To" option, and then select the drive you want to copy the file to.

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(e) Steps to create a new folder

1. Go to My Computer or Windows Explorer; open the folder in which you want to create a new

folder by double clicking on it.

2. Go to the File menu, point to New, and then click on the "Folder" option.

3. The new folder appears with a temporary name.

4. Type a name for the new folder, and then press ENTER.

Steps to change the name of a file or folder

1 Go to My Computer or Windows Explorer

2 Click on the file or folder you want to rename.

3. Go to the File menu, and Select/Click "Rename" option.

4. Type a new name for the file or Folder, and then press ENTER.

Note :

As Windows 95 supports long file name, a filename can be up to 255 characters, including spaces.

However, it cannot contain any of the following characters:

\ / : * ? " < > |

8.7 NETWORK NEIGHBORHOOD

A Network is a group of Computers connected to each other to share available resources such as

storage and printers. Network neighborhood takes the ability of My Computer and extends them one

step further, by giving you with the ability to view all of the Computers connected in workgroup or

network, and see what drives or Printers may be available for use. If you double click on one of the

Computers, any resources that Computer shares with others in the workgroup like- drives, directories

or printers will be listed

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Fig.8.7

When connected to a network, the Network Neighborhood icon appears on the desktop. To browse

through the computers in the workgroup and the computers on the entire network, double click on the

icon Network Neighborhood.

Fig 8. 8

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1.8 RECYCLE BIN

The files deleted by you are put in the Recycle Bin, a holding place for files that are no longer needed.

There you can also drag and drop files for quick deleting. They are, however, not actually removed

from the hard disk until the user "empty" the Recycle Bin.

It is a safety feature, built in to protect you against the possibility of deleting something you should

not have.

Fig. 8.9

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8.9 FIND

Using Windows 95 it is easy to locate files and folders on the computer. One way is to browse

through folders in My Computer. But if you want to find something quickly, you can use the Find

command on the Start menu.

Fig. 8.10

Click on the Start button and select "Find" option. Now select the Option " Files or Folders". This will

activate the Find Dialog box. In the Find dialog box, type the name of the file or folder you are

looking for, and then click Find Now. You can also use wildcard character to Find files

Fig. 11

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8.10 WORK WITH PROGRAMS

Windows 95 provides higher level of flexibility in terms of installing and removing programs.

To install a program from a floppy disk or CD-ROM

1. Select Control Panel from the Settings option of Start Menu

2. Double Click on the Add/Remove Programs icon.

3. Follow the instructions on your screen.

To install a program from a network

1. Click here to open the Add/Remove Programs dialog box.

2. if the Install/Uninstall tab is selected, and your computer is already connected to a network,

click Install button, and then click Next. Follow the instructions on your screen.

Note

If you do not have a Network Install tab in the Add/Remove Programs dialog box, this feature has not

been enabled on your computer, your network, or both. See your system administrator.

If you are not already connected to the shared folder you want to install from, you must connect to it

by using My Computer or Windows Explorer, or type the path to it in the text box.

To remove a program from your computer

1. Select Control Panel from the Settings option of Start Menu

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2. Double Click on the Add/Remove Programs icon.

3. Follow the instructions on your screen.

Note

Only programs that were designed for Windows 95 can be removed by using Add/Remove Programs.

For all other programs, check the program's documentation to determine which files should be

removed.

8.11 MS-DOS WINDOW

Windows 95 provides the flexibility of executing most of the DOS commands or DOS based program

without going out of Windows 95 GUI. To use DOS prompt;

1. Click the Start button, and then point to Programs.

2. Click/Select MS-DOS Prompt.

Fig 8.12

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Tips

To view the toolbar, click the MS-DOS icon in the title bar, and then click Toolbar.

To switch between a full screen and a window, press ALT+ENTER.

To quit MS-DOS, click or type Exit at the command prompt.

8.12 CHANGE WINDOWS SETTINGS

Windows 95 provides tools to change the look and feel of the desktop window. Using these tools you

can change the desktop background, wallpaper and lots of other settings according to your choice.

To activate these tools, right click on the windows. This will display a menu now select the Properties

option.

You can also activate these tools from Control panel by selecting the Display icon.

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Fig 8.13

Desktop Background

To change the background of the desktop

Right Click on the Desktop to view the Display properties.

In the Pattern or Wallpaper list, click the pattern or wallpaper you want to use.

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Fig. 8.14

Tips

To cover the entire screen with wallpaper image, click Tile.

To center a wallpaper image, click Center.

Patterns and wallpaper can be used simultaneously. However, you will not be able to see the

pattern, if Title is selected.

Similarly all other option such as Appearance, Screen Saver and Settings can be used. Using the

Settings option, one can select the number of colors, pixel type and display adapter for the system.

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8.13 SHUT DOWN THE COMPUTER

Click the Start button, Click the Shut Down button, and then select the option Shut down the

Computer and click on the Yes button.

Fig. 8.15

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Important

Do not turn off your computer until the "You can now safely turn off your computer" message

appears.

Choose the best answer for the following questions.


1. Which of the following is introduced exclusively in Windows95?

(a) Control panel

(b) File manager

(c) Start button


2. What is the Windows 3.x series equivalent to Windows Explorer in Windows95?

(a) Program manager

(b) File manager

(c) Print manager


3. Answer whether the following statement is True (T) or False (F).

(a) Windows 95 supports file name of 255 characters including space in between.

(b) Windows 95 does not support Ms-DOS based application.

(c) Windows 95 is a application software.

(d) In Windows 95 desktop icons can be created, but can not be deleted.

4. Fill in the blanks

(a) Inbox in Windows 95 is used for ______________________.

(b) GUI stands for ________________________.

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This lesson introduced you to one of the most popular and widely used GUI operating system in

desktop environment. In the beginning it discussed what is GUI and its usefulness. It explained the

new features of Windows95 and hardware requirement for installation. You also learned about

various Windows 95 icons and their usability. Here we discussed how to do file management in

Windows 95, and also we learned how to change look and feel of Windows 95 desktop according to

user requirement.


(c) Briefly explain, how Windows95 is different from Windows 3.x series.

(d) Explain what do you understand by multitasking?

(e) What is the minimum hardware requirement for installing Windows95 software?

(f) What is the purpose of recycle bin?

(g) Explain the steps involved to shut down Windows95.



1. (c) 2. (b) 3.(a) True (b) False (c) False (d) False 4. (a) Getting e-mail, (b) Graphical User

Interface.

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