Introduction to Computer Programming - CPU1141 · 2020. 6. 14. · Introduction to Computer Programming - CPU1141 Faculty of Natural Sciences Department of Mathematics & Computer

Introduction to Computer Programming - CPU1141 Faculty of Natural Sciences Department of Mathematics & Computer Science Bachelor of Science Degree Computer Science: Level 3

Course Details • Printed Materials: ▫ Introduction to Computer Programming Course

Material ▫ Introduction to Computer Programming Practical

Guide • Day Schools • Practical Sessions • Practical Test • Continuous Assessment Tests [NBT I & NBT II] • Final Exam

Course content • Computer Programming • Introduction to Pascal ▫ Data Types & Variables ▫ Operations & Expressions ▫ Control Structures ▫ Functions & Procedures ▫ Arrays & Pointers

• Introduction to C ▫ Data Types & Variables ▫ Operations & Expressions ▫ Control Structures ▫ Input output functions ▫ Arrays, Strings, Pointers and Functions ▫ File Handling

Today’s Sequence

• Computer Programming • Introduction to Pascal • Data Type & Variables • Operations & Expressions • Control Structures

Learning Outcome

• Aim: ▫ To provide a brief introduction to the computer

programming

• You will be able to: ▫ Get an idea about programming and the level of

languages

Introduction

• This chapter discuss the reasons for learning programming and level of languages

What is a program?

A program is a set of step by step instructions that directs the computer to do the tasks you want it to do and produce the result you want

Introduction

Why programming? • Programming helps you understand computers • Writing few simple programs increases your

confident level • Learning programming lets you find out how

you solve problems analytically.

Introduction

Terms: • Programming Language: A set of rules that provides a way of telling a

computer what operations to perform

Levels of Languages • Programming Language mainly divided into two

namely “Lower” and “Higher” • Lower:

How close it is to the language of the computer eg: 1’s and 0’s

• Higher: How close it is to the language of people use eg: similar to English language

Levels of Languages

• There are five levels of language: ▫ Machine Language ▫ Assembly Language ▫ High-Level Language ▫ Very High-Level Language ▫ Natural Language

Levels of Languages Machine Language: • The lowest level of programming language • Only understood by the computer and

IMPOSSIBLE for humans • Each type of computer has its own machine

language • Represent the data and program instructions as

1s and 0s • These 1s and 0s are corresponded to the ON and

OFF electrical states in the computer respectively.

Levels of Languages Assembly Language: • Used abbreviation which are easily remembered

by human to replace 1s and 0s ▫ Eg: ADD, MUL

• Each type of computer has its own assembly language

• Requires a translator called “Assembler” to convert the assembly language program into machine language

Assembly Language

Machine Language

Translator ( Assembler)

Levels of Languages High-Level Language: • Began using of High-Level language in early 1960 • Programs were written in similar to English

Language • Eg: COBOL, Fortran, Pascal, C, C++, C# • Runs on any machine • Benefits: ▫ Convenient ▫ More production with less effort ▫ Tend to focus on solving much complex problems

Levels of Languages High-Level Language: • A translator called “Compiler” is needed to translate

the symbolic statements into machine language

• Programmers write programs in a form called “Source Code”

• Compiler is used to translate source code to machine language

• The compiler produces an intermediary form called “object code”

• Object code is much similar to a computer’s machine language

Translator ( Compiler)

Source Code Object Code

Levels of Languages

Very High-Level Language: • These are known by their generation number;

fourth generation languages (4GLs) • 4GL languages are programming languages

closer to human languages than typical high level languages

• Mostly used to access databases

Levels of Languages

Natural Language: • These are used for artificial intelligence and

neural networks • Eg: Prolog • Prolog is used to develop Expert Systems

PART A: PASCAL LANGUAGE

Learning Outcomes

Aims: • To provide a brief introduction to the Pascal

Language You will be able to: • Identify the major segments of a Pascal program • Write a simple Pascal program

Introduction

Major segments of a Pascal Program: • A Pascal program has three major segments: ▫ The program identification and description

segment ▫ The declaration segment ▫ The main body of the program

Introduction Segment 1: Program Identification & Description: • The structure of the first line in the program

• Explanation:

PROGRAM example01 (INPUT, OUTPUT);

Code Description

PROGRAM First word of any Pascal program

example01 Program Name

(INPUT, OUTPUT) To indicate whether program has any input or output

; Last character of any Pascal line

Introduction Segment 1: Program Identification & Description: • Every Pascal line should end with a semicolon

“;” • So, it is possible to spread one Pascal line over a

no. of horizontal lines • Pascal is not case sensitive language • Upper case characters were used to represent

keywords in examples

Introduction Segment 1: Program Identification & Description: Rules in Pascal for giving program name to a program: • Name has to start with a letter of the alphabet “a-z”

or an underscore “_” • Do not start a program name with a digit or special

characters “#, ?” • The other items in a name could contain any

keyboard character • There should be no blank space within a name

▫ Eg: if a name contain 2 components, it can be separated using an underscore

• Do not include keywords used in Pascal for naming a program

Introduction Segment 1: Program Identification & Description: Keywords in Pascal:

And Downto If Or Then Array Else In Packed

To Begin End Label Procedure

Type Case File Mod

Program

Until Const For Nil Record Var Div Function

Not Repeat While Do Goto Of Set with

Introduction Segment 2: Declaration: • Define variables, constants etc. in the program • All of the entities going to be used in the

program must be defined • For that, data types and variables will be deeply

discussed in chapter 2

Introduction Segment 3: Main body of the program: • Main body of the program is written within

BEGIN-END pair • This is equivalent to a set of brackets • It is possible to have any no. of BEGIN-END

pairs in a single program • However, no. of BEGIN statements should

match no. of END statements

Introduction

Segment 3: Main body of the program: • Example:

PROGRAM firstprogram (OUTPUT); BEGIN WRITELN (‘Hello my friend’); END

Introduction Displaying output : WRITELN, WRITE command • To display several lines of text you need a

WRITELN statement for each line • Example PROGRAM lineOftext (OUTPUT);

BEGIN WRITELN (‘Hi there’); WRITELN (‘How are you today?’); WRITELN (‘Are you ready for Pascal’) END

Introduction Displaying output : WRITELN, WRITE command • Explanation: ▫ Each statement must be separated from the next

one with semicolon • This is the only way the compiler can recognize

the end of the statement • But, you may skip the semicolon in the last

statement of the program block

Introduction Displaying output : WRITELN, WRITE command • Output:

• The WRITELN statement displays a line of text followed by a new line

• Use WRITE statement, if you want to display two string on the same line

Hi there How are you today? Are you ready for Pascal

Introduction Displaying output : WRITELN, WRITE command • Code:

• Output:

Hi there How are you today? Are you ready for Pascal

PROGRAM Twolines (OUTPUT); BEGIN WRITE (‘Hi there’); WRITELN (‘How are you today?’); WRITELN (‘Are you ready for Pascal’) END

Introduction Displaying output : WRITELN, WRITE command • To display the content of the variable you need a

WRITELN or WRITE statement without using quotes

• Also WRITELN or WRITE can be used to display text and content of variables in the same statement by separating them with a coma

WRITELN (‘The Result is =’, r);

Introduction

Comments: • Comments are enclosed with braces or bracket

and a star in cases

• Can be included in anywhere in the program • Compiler ignores the comment • Comments are useful to explain the program to a

human reader

(*This is a comment*)

Introduction

Indentations: • It is customary to a line each BEGIN-END pair

along the same vertical line • Eg: five horizontal spaces should be kept from

the previous block when starting a new

Learning Outcomes

Aims: • To provide an overview of some significant

features of the Pascal Language You will be able to: • Identify the data types in Pascal Language • Get an idea about declaring the variable and

constant • Learn how to format you numeric outputs

Data Types

• When writing program, it is necessary to store information in component form to manipulate them later

• For that, variables are used • Every variable should have a name and a type • Type mean the values that the variable can take • It helps to determine the amount of memory

space to store a variable

Data Types

• Variable should be declared in the declaration section

• There are no. of standard data types ▫ Integer ▫ Real ▫ Boolean ▫ Char

Data Types Integer: • This type allows to represent, store and process integer

numbers • Contains all the integer values in the range of;

-maxint,…., -1, 0,+1,….,+maxint

• The value of maxint is 32767 on minicomputer • 2147483647 in large computers • So, outcome of any arithmetic on integer values will be

correct only of they are in ± maxint • Or else, the answers will be unpredictable (overflow)

Data Types

Real: • Real numbers are numbers with decimal values ▫ eg: 14.65 meters, 9.2 seconds

• The limit of the real numbers which can be stored in a computer is very large compared to integers

Data Types

BOOLEAN: • Can only have two values ▫ True ▫ False

• Normal arithmetic operations cannot be performed on a boolean variable

Data Types Char: • Can hold any single given character at a time ▫ Eg: if x is char variable, it can hold only one

character at a time • Blank space also considered as a character • When assigning char variable, enclosed the

character with single quotes ▫ Eg: ‘A’

• Each char requires a one byte of memory

Variables

• Variable is a location in memory referenced by a variable name (identifier) where a data can be stored

• Can hold only one value at a time during the program execution

• Values can be changed during several executions

Variables

Variable Names: • A variable must be declared before using the

program • Variables are the identifiers • When declaring a variable, it consists with ▫ Sequence of letters and digits ▫ First character should be either a letter or

underscore ▫ Keywords cannot be used

Variables Variable Declaration: • The type and the name of a variable should be

initiate before using a program • It should be declared in the declaration part in

the program • Declaration part starts with the keyword VAR • Eg:

VAR gross_salary : REAL; n, i : INTEGER name : CHAR;

Variables Variable Declaration: • Eg1:

Following equation gives the total resistance R of three resisters r1, r2 and r3 connected in parallel

• The programmer should consider before writing the program for the above problem, ▫ Read the values for r1, r2 and r3 ▫ Calculate R ▫ Print the result

Variables Variable Declaration: • Eg1:

PROGRAM calc_of_resistance (INPUT, OUTPUT); VAR r1,r2,r3,R : REAL; BEGIN WRITE (‘Enter three resisters:’); READLN (‘r1,r2,r3’); R :=1/r1+1/r2+1/r3; R := 1/R; WRITELN (‘Total Resistance is’, R); END.

Line 1

Line 2 Line 3 Line 4 Line 5 Line 6 Line 7 Line 8 Line 9 Line 10

Variables Variable Declaration : • Explanation:

Line 1: Program naming Line 2: variable naming and declaration Line 4 - 10 : solving the given problem Line 6: Reading the user inputs for r1, r2, and r3 Line 7: calculating the R with given r1, r2 and r3 Line 8: replacing the R with value of 1/R Line 9: printing the calculated value for R

Variables Variable Declaration : how practically run a program for Eg1 • Enter the given program • Save and compile it • Compiler show if any syntax errors available • Fix them until the program is free from syntax errors • When the compilation is successful you are ready to run

the program • The computer waits until you put three values for r1, r2

and r3 when the program runs • Once entered values, the total resistance will be

displayed Enter three resisters: 2 3 4

Total Resistance is : 9.2307692308E-01

Variables

Reading from the keyboard: READLN, READ: • READLN and READ commands in Pascal program

are used to read values given by user to produce results

• READ: is used to read a value of one variable at a time ▫ Eg: READ (variable) / READ (r1);

• READLN: is used to read the value of one or more variables ▫ Eg: READLN (variable_list) / READLN (r1,r2,r3);

Variables

Formatting Output: • You can format your output in a fixed notation • Eg1:

• The format 8:2 determines a field width of 8

positions including 2 decimal places

WRITELN (‘Total Resistance is’, R:8:2);

Total Resistance is : *******0.92

Variables Constants : • A constant remains unchanged throughout the

execution of the program • It is often useful to give a symbolic name

(identifier) to a constant • This can then be used throughout the program

whenever the value of the constant is required ▫ Eg: if the program replace 3.14159 with pi, it

would be much easier to read

Variables

Constants : • Keyword CONST is used to declare constants in

the declaration segment of the program ▫ Syntax:

▫ Example:

CONST identifier = constant;

CONST pi = 22/7;

Learning Outcomes

Aims: • To provide an overview of some important

features of the Pascal Language You will be able to: • Learn various operators and their precedence in

Pascal

Types of Operators

• The operators define how the variables and constants in and expression will be manipulated

• Three operators allowed in Pascal; ▫ Arithmetic Operators ▫ Relational Operators ▫ Logical Operators

Types of Operators

Expression: • An Expression is a combination of variables,

constants and operators written according to the syntax of the language

• Eg: ▫ a + b ▫ a + 200*w ▫ total + x/3

Types of Operators Arithmetic Operators: • Basic arithmetic operations

• + : addition • - : subtraction • * : multiplication • / : division

• These operators act as usual operators • The entities on which the operators are applied are

called as Operands • Eg: o 5+3 o Here, 5 and 3 are operands and + is the operator

Types of Operators

Arithmetic Operators: • Additionally, ▫ DIV and MOD are used as operators

• Eg: ▫ For integer division, DIV is used [a DIV b] Divide a by b and give the divisor 10 DIV 5 = 2

▫ MOD is used to get the remainder of integer division [a MOD b] Divide a by b and give the remainder 10 MOD 5 = 0

Types of Operators Relational Operators: • A relational operator is used to make

comparisons between two expressions • Allowed relational operators in Pascal;

Operator Usage

= Equal to

< Less than

> Grater than

Not equal to

= Grater than or equal to

Types of Operators Relational Operators: • Each one of the operator compares its left hand

side operand with its right hand side operand • Operands can be variables or expressions • The whole expression involving the relational

operator then evaluates to an integer

Types of Operators

Logical Operators: • Logical operators let you combine two or more

relational expressions into a single expression which evaluates to either true or false

• Eg for Pascal logical operators; ▫ NOT ▫ AND ▫ OR

Types of Operators

Logical Operators: AND Operator

Expression 1 Expression 2 Result

True True True

True False False

False True False

False False False

Types of Operators Logical Operators: OR Operator

Logical Operators: NOT Operator

Expression 1 Expression 2 Result

True True True

True False True

False True True

False False False

Expression Result

True False

False True

Operator Precedence

• Operators are used in a program according to their priority order (precedence) as follows;

Operation Symbol Precedence

Multiplication *, /, DIV, MOD 1

Addition +, - 2

Relation =, , , =

3

Logical NOT 4

AND 5

OR 6

Operator Precedence

• Brackets always have higher precedence than all the above operators

• If bracket used; ▫ The content inside the innermost pair of brackets

will be evaluated first • When several operations having same

precedence; ▫ Evaluation will be done in left to right

Character operations

• In addition to the comparison statements, following are used as operators ▫ ORD ▫ SUCC ▫ PRED ▫ CHR


ORD: • ORD function has one argument which should

be a character or a character variable • It will return an integer number corresponding

to the internal representation • If ASCII is used, then the ORD function will

return the corresponding ASCII value


CHR: • CHR function takes an integer as an input

argument and returns the corresponding character

• Opposite of the ORD function SUCC: • SUCC function takes a single character or a

character variable as an argument • Returns the next character


PRED: • PRED function takes a single character or a

character variable as the input argument • Returns the previous character

Learning Outcomes

Aims: • To provide an overview of control structures in

Pascal Language You will be able to: • Use the major control structures such as

repetition loops conditional statements in Pascal Language

Control Structures

• For practical use of computers, selective and repetitive expressions are necessary

Conditional statements: • There are two main types of statements in Pascal

for selective operations ▫ IF-THEN ▫ CASE

Conditional Statements IF-THEN: • Use when we have to select a set of actions from

two sets depending on a condition

• However, the ELSE is optional • IF-THEN and IF-THEN-ELSE statements are

treated as one compound statement • So, a semicolon is used only at the end

IF condition THEN statement ELSE statement;

Conditional Statements IF-THEN: • The condition with IF must produce a boolean result • The boolean expression is evaluated ▫ If it is true, The statements following THEN will be executed

▫ Otherwise, The statements following ELSE will be executed

• If there are more than one statement with IF-THEN or ELSE statements, they are grouped with BEGIN-END

Conditional Statements IF-THEN: • Example:

• ELSE-IF statements are used to make multi-way decision based on several conditions

• This is done by cascading several comparisons • As soon as one of a else-if gives a true result,

corresponding statements will be executed and no further comparisons will be performed

IF A > B THEN max := A ELSE max := B;

Conditional Statements ELSE-IF: • Example:

IF (result >= 75) THEN WRITELN (‘Passed: Grade A’) ELSE IF (result >= 60) THEN WRITELN (‘Passed: Grade B’) ELSE IF (result >= 45) THEN WRITELN (‘Passed: Grade C’) ELSE WRITELN (‘Failed’);

Conditional Statements

Nested IF Statements: • IF statement inside the other IF statements are

known as Nested IF Statement • If there is a problem that involved with more

than two alternatives courses of action can be coded using nested if statement

• In the nested if, the else statement is always associated with the nearest if statement

Conditional Statements Nested IF Statements: • Example:

IF i > 10 THEN BEGIN WRITELN (‘i is more than 10’); IF j > 3 THEN WRITELN (‘j is more than 3’); ELSE WRITELN (‘j is less than or equal to 3’); END

ELSE WRITELN (‘i is less than equal to 10’);


IF Statements: Example: • Write a program in Pascal to read a set of

numbers and to find the maximum value. The program should be terminated when a-1 is read

• Refer page 22


CASE Statements: • CASE statement allows the choice of one out of

several sets of action • The selection is done by matching the value of

the selector with a case label attached to each statement


CASE Statements:

CASE selector OF case label1: statement case label2: statement . . case labeln: statement ELSE statement END;

Conditional Statements CASE Statements: • Depending on the selection value, the case

statement will pick the appropriate action • If the SELECTOR has a value for which no

action has been described, then the ELSE statement is executed

CASE month OF 1,3,5,7,8,10,12: no. of days := 31; 2 : no. of days := 28; 4,6,9,11 : no. of days := 30; END;


CASE Statements: • If there is value range then the CASE statement

are written as follow;

CASE mark OF 0..39 : grade := ‘F’; 40..59 : grade := ‘C’; 60..79 : grade := ‘B’; 80..100: grade := ‘A’; END;


CASE Statements: Example: • Write a program to read a number between 1-7.

if the number is 1 then print “Monday”. If it is 2 then print “Tuesday” and so on.

CASE Statements: Example: PROGRAM eg_case(INPUT, OUTPUT); VAR number : INTEGER; BEGIN WRITELN(‘Enter a number within 1-7:’); READLN(number); CASE number OF 1 : WRITELN(‘Monday’); 2 : WRITELN(‘Tuesday’); 3 : WRITELN(‘Wednesday’); 4 : WRITELN(‘Thursday’); 5 : WRITELN(‘Friday’); 6 : WRITELN(‘Saturday’); 7 : WRITELN(‘Sunday’); ELSE WRITELN(‘Invalid day of the week!!!’); END; END.

Repetition

• There are three main types of statements for repeating certain instructions ▫ REPEAT UNTIL Loop ▫ WHILE Loop ▫ FOR Loop

Repetition REPEAT-UNTIL Loop: • This will repeat everything that is inside this

loop, as the condition given with the until statement is false

• When the statement becomes true, the loop is completed

• Any statements after UNTIL are then executed • The expression supplied with the UNTIL

statement must give a boolean value

Repetition REPEAT-UNTIL Loop: • Example:

REPEAT statement(s) UNTIL boolean_expression;

x:=1; REPEAT WRITELN(x); x:= x +1; UNTIL x > 10;

Repetition

REPEAT-UNTIL Loop: Example: • Write a program to read a set of integer numbers

and to calculate the total and the average. The end of the list of numbers is denoted by -1.

REPEAT-UNTIL Loop: Example PROGRAM eg_repeatuntil(INPUT, OUTPUT); CONST endmark = -1; VAR value, total, count, avg : INTEGER; BEGIN total := 0; count := 0; avg := 0; REPEAT WRITELN(‘Enter a number:’); READLN(value); count := count + 1; total := total + value; avg := total DIV count; WRITELN(‘The total is: ’, total, ‘and the average is: ’, avg); UNTIL value = endmark; END.

Repetition REPEAT-UNTIL Loop: Example: • This program will add the endmark (-1) to the

output.

• So this should be corrected as follows

REPEAT-UNTIL Loop: Example PROGRAM eg_repeatuntil(INPUT, OUTPUT); CONST endmark = -1; VAR value, total, count, avg : INTEGER; BEGIN total := 0; count := 0; avg := 0; WRITELN(‘Enter a number:’); READLN(value); REPEAT count := count + 1; total := total + value; avg := total DIV count; WRITELN(‘The total is: ’, total, ‘and the average is: ’, avg); WRITELN(‘Enter a number:’); READLN(value); UNTIL value = endmark; END.

Repetition REPEAT-UNTIL Loop: Example: • This program will do the answers correctly as

follows;

Repetition

WHILE Loop: • WHILE loop checks the condition at the

beginning • So the constants within the loop may or may not

be executed • WHILE loop will be executed as long as the

condition is true • If there are more than one statement with the

WHILE statement, they can be grouped with BEGIN-END

Repetition WHILE Loop: • Example:

WHILE boolean_expression DO statement;

x:=1; WHILE x

REPEAT-UNTIL Loop: Example using WHILE PROGRAM eg_while(INPUT, OUTPUT); CONST endmark = -1; VAR value, total, count, avg : INTEGER; BEGIN total := 0; count := 0; avg := 0; WRITELN(‘Enter a number:’); READLN(value); WHILE value endmark DO BEGIN count := count + 1; total := total + value; avg := total DIV count; WRITELN(‘The total is: ’, total, ‘and the average is: ’, avg); WRITELN(‘Enter a number:’); READLN(value); END; END.

Repetition FOR Loop: • Used in repeating a loop for several times

• a, b and c could be any data type for which it is possible to go from b to c in a finite no. of increments ▫ a,b and c are real variables ▫ Most cases they will be integers

FOR a := b TO c DO

Repetition FOR Loop:

• In this loop, the values are decreased from b to c • If there are more than one statement with the

FOR statement, they are grouped with BEGIN-END

FOR a:=b DOWNTO c DO

Repetition FOR Loop:

• Example:

FOR control_variable:= initial TO/ DOWNTO DO statement;

FOR x:= 1 TO 10 DO WRITELN (x);

FOR x:= 10 DOWNTO 1 DO WRITELN (x);

REPEAT-UNTIL Loop: Example using FOR LOOP to find the total and average of

5 numbers PROGRAM eg_for(INPUT, OUTPUT); VAR value, total, count, avg : INTEGER; i : INTEGER; BEGIN total := 0; count := 0; avg := 0; FOR i := 1 TO 5 DO BEGIN WRITELN(‘Enter a number:’); READLN(value); count := count + 1; total := total + value; avg := total DIV count; WRITELN(‘The total is: ’, total, ‘and the average is: ’, avg); END; END.

Introduction to Computer Programming - CPU1141 · 2020. 6. 14. · Introduction to Computer Programming - CPU1141 Faculty of Natural Sciences Department of Mathematics & Computer

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