Programming Languages: Telling the Computers What to Do Chapter 16.

Programming Languages: Telling the Computers

What to Do

Chapter 16

Objectives

• Describe what programmers do and do not do

• Explain how programmers define a problem, plan the solution and then code, test, and document the program

• List and describe the levels of programming languages – machine, assembly, high level, very high level, and natural

• Describe the major programming languages in use today

• Explain the concepts of object-oriented programming

Contents

• Program

• Programmers

• The Programming Process

• Choosing a Language

• Traditional Programming

• Object-Oriented Programming

• Learning to Program

Program

Set of instructions written in a programming language that tells the

computer what to do

Programmers• Prepare instructions that make up the program

• Run the instructions to see if they produce the correct results

• Make corrections

• Document the program

• Interact with– Users– Managers– Systems analysts

• Coordinate with other programmers to build a complete system

The Programming Process

• Defining the problem

• Planning the solution

• Coding the program

• Testing the program

• Documenting the program

The Programming ProcessDefining the Problem

• What is the input

• What output do you expect

• How do you get from the input to the output

The Programming ProcessPlanning the Solution

• Algorithm – detailed solution to a problem

• Design tools– Flowchart– Pseudocode

• Desk-checking

• Structured walkthrough

The Programming ProcessPlanning the Solution

Accept series of numbersand display the average

The Programming ProcessPlanning the Solution

Accept series of numbers and display the average

The Programming ProcessCoding the Program

• Translate algorithm into a formal programming language

• Syntax

• How to key in the statements?– Text editor– Programming environment – Interactive

Development Environment (IDE)

The Programming ProcessTesting the Program

• Translation – compiler– Translates from source module into object module– Detects syntax errors

• Link – linkage editor (linker)– Combines object module with libraries to create

load module– Finds undefined external references

• Debugging– Run using data that tests all statements– Logic errors

The Programming ProcessTesting the Program

The Programming ProcessDocumenting the Program

• Performed throughout the development

• Material generated during each step– Problem definitions– Program plan– Comments within source code– Testing procedures– Narrative– Layouts of input and output– Program listing

Choosing a Language

• Choice made for you– What is available?– Required interface

• What do you know best?

• Which language lends itself to the problem to be solved?

Language Generations

• Low levels closer to binary

• High levels closer to human code

• Five Generations:– Procedural Languages

• Machine language• Assembly language• High-level language – 3GL

– Nonprocedural Languages• Very high-level language – 4GL• Natural language – 5GL

Machine Language

• Written in strings of 0 and 1

• Only language the computer understands

• All other programming languages are translated to machine language

• Computer dependent

Assembly Language

• Mnemonic codes

• Names for memory locations

• Computer dependent

• Assembler translates from Assembly to machine language

3GLHigh-Level Languages

• 1960s

• Languages designed for specific types of problems and used syntax familiar to the people in that field– FORTRAN: math– COBOL: business

• Compile translates from high-level language to machine language

4GLVery High-Level Languages

• Programmer specifies the desired results; the language develops the solution

• Ten times more productive with a 4GL than a procedural language

• Query Languages– Retrieve information from databases– Easy to learn and use

5GLNatural Languages

• Resemble natural or spoken English

• Translates human instructions into code the computer can execute

• Commonly used by non-programmers to access databases

Third Generation LanguagesTraditional Programming

• Describe data

• Describe procedures or operations on that data

• Data and procedures are separate

Third Generation Languages

• FORTRAN– 1954– Represent complex mathematical formulas– C/C++ has replaced FORTRAN

• COBOL– 1959– Business– Large complex data files– Formatted business reports

Third Generation Languages

FORTRAN

Third Generation Languages

COBOL

Third Generation Languages

• BASIC– 1965– Popularity grew with PC popularity (1970s)– Easy to learn– Used little memory

• RPG– 1965– Report generation – quickly creates complex

reports

Third Generation Languages

BASIC

Third Generation Languages• Visual Basic

– 1987– Create complex user interfaces– Uses standard Windows features– Event-driven – user controls the program

• C– 1972– Efficient code– Portability

• C++– Enhancement of C

Third Generation Languages

C++

OOPObject-Oriented Programming• Object

– Self-contained unit of data and instructions– Includes

• Related facts (data)• Related functions (instructions to act on that data)

• Example– Object: cat– Data: feet, nose, fur, tail– Functions: eat, purr, scratch, walk– Cat: Kitty, Susan

OOPObject-Oriented Programming• Encapsulation – describes the objects self-

containment

• Attributes – the facts that describe the object

• Methods / operations – the instructions that tell the object what to do

• Instance – one occurrence of an object

• Messages – activate methodsExample: A walk message causes Kitty to move

OOPObject-Oriented Programming• Class – defines characteristics unique to all

objects of that class

• Inheritance – Objects of a class automatically posses all of the characteristics of the class from which it was derived

• Subclass – inherits characteristics from class and defines additional characteristics that are unique

OOPObject-Oriented Programming

ExampleClass: AnimalSubclass: CatSubclass: Persian catInstance: Kitty

Objects can be reused

OOPObject-Oriented Programming

Languages

• C++Can write both structured and object-oriented code

• Visual BasicRudimentary features of object-oriented language

Third Generation Languages

Java

• Cross-platform

• Java Virtual Machine (JVM)– Sits on top of computer’s regular platform– Translates compiled Java code into

instructions for the specific platform

• Applets

OOPObject-Oriented Programming

Using Objects in BusinessClass: CustomerSubclass: Retail or WholesaleInstance: John Smith

Retail and Wholesale customers automatically inherit customer address since it is part of the Customer class

Learning to Program

• Enroll in courses

• Read

• Use tutorials

• View Sample code

• Write code (start small)

• Use Help