CHAPTER 4 : Part 2INTRODUCTION TO SOFTWARE DEVELOPMENT:PROGRAMMING & LANGUAGES

Module Objectives

• At the end of the module, students should be able to:

– List and describe the levels of programming languages:

machine, assembly, high level, very high level, and natural

– Describe the major programming languages that are in

use today

– Explain the concepts of object-oriented programming

What is Programming ?

• Computer program – a series of instructions that directs a computer to

perform task.

• Programming language – a set of words, symbols, and codes that enables a

programmer to communicate instructions to a computer.– a set of rules that provides a way of telling the computer

what operations to perform

Levels of Programming Languages

• Lower-level languages – more like the 0s and 1s the computer itself uses

• Higher-level languages – more like the languages people use

• Divided into five generations1. Machine language

2. Assembly languages

3. High-level languages

4. Very high-level languages

5. Natural languages

1. Machine Language

• Programs and memory locations are written in strings of 0s and 1s

• Problems with machine languages– Programs are difficult to write and debug– Each computer has its own machine language

• Only option available to early programmers

2. Assembly Languages

• Substitute mnemonic codes for 0s and 1s – For example, A for add, C for compare, etc.– Use names rather than binary addresses for memory

locations

• Require an assembler to translate the program into machine language

• Still used for programming chips and writing utility programs

• Example: MOV AL, 61h ; Load AL with 97 decimal (61 hex)

3. High-Level Languages

• Transformed programming– Programmers could focus on solving problems

rather than manipulating hardware– Programs could be written and debugged much

more quickly

• Requires a compiler to convert the statements into machine language– Each computer has its own version of a

compiler for each language

4. Very High-Level Languages

• Also called fourth-generation languages (4GLs)

• Considered nonprocedural languages– The programmer specifies the desired results,

and the language develops the solution– Programmers can be about 10 times more

productive using a fourth-generation language than a third-generation language

5. Natural Languages

• Resemble written or spoken English– Programs can be written in

a natural syntax, rather than in the syntax rules of a programming language

• The language translates the instructions into code the computer can execute

Major Programming Languages

• FORTRAN• COBOL• BASIC• RPG

• Visual Basic• C

• Java

FORTRAN

• The first high-level language• Stands for FORmula

TRANslator• Used primarily for

engineering, mathematical, and scientific tasks

COBOL

• Stands for COmmon Business-Oriented Language

• Used primarily for business requirements– Processes large data files– Produces well-formatted

reports

BASIC

• Stands for Beginners’ All-Purpose Symbolic Instruction Code

• Developed to teach programming to college students

• Became very popular with the introduction of the microcomputer

RPG

• Stands for Report Program Generator• Designed to allow rapid creation of

reports– Programmer simply describes the source

data and desired report format

Visual Basic

• Allows programmer to create Windows-like user interfaces– Programmer drags a control

(button, text box, etc.) onto the form

– VB creates the code associated with that control

• VB is event-driven– The user controls the program

C

• Originally designed to write systems software– Offers the ease of use of a

high-level language with the efficiency of an assembly language

• Very portable – can be used with virtually every combination of computer and operating system

#include <stdio.h> main(){ int number; printf("Enter an integer\n"); scanf("%d",&number); printf("Integer entered by you is %d\n", number); return 0;}

Java• A network-friendly programming language that

permits a piece of software to run directly on many different platforms– Allows programmers to write one version of the

program, rather than a separate version of each platform

• Very useful for Internet development– Java applets can run in the user’s Web browser

public class HelloWorld { // method main(): ALWAYS the APPLICATION entry

point public static void main (String[] args) {

System.out.println ("Hello World!"); }

}

Object-Oriented Programming

• Object – a self-contained unit that contains both data and its related functions

• Key terms in object-oriented programming– Encapsulation – an object isolates both its data and its

related instructions– Attributes – facts that describe the object

• Also called properties

– Methods – instructions that tell the object to do something

– Messages – an outside stimulus that results in the change of the state of an object

Using Objects

• Programmers define classes of objects

– The class contains all attributes that are unique to objects of that class

– An object is an instance (occurrence) of a class

• Objects are arranged hierarchically in classes and subclasses

– Subclasses are derived from classes– Inheritance – a subclass possesses all

attributes of the class from which it is derived

– Additional attributes can be coded in the subclasses

Activating the Object

• A message is sent to the object, telling it to do something– The object’s methods tell it how to do it

• Polymorphism – each object has its own way to process the message– For example, the class may have a Move

method, but each subclass implements that method differently

Object-Oriented Languages

• C++• Java• C#• Visual Basic

C++

• An enhancement of the C language– Includes all features of C – Adds support for object-oriented programming

• Can be used as simply an improvement of C, without the object-oriented features

Java

• A pure object-oriented program• Used to create small programs called

applets– Applets can be delivered over the Web and run

on any platform

C#

• Microsoft’s answer to Java• Has the same advantages over C++ that Java

has• Designed to work within Microsoft’s .NET

environment– .NET is designed for building, deploying, and

running Web-based applications

Visual Basic

• Previous versions supported some object technology

• The current version, VB.NET, is the first to support inheritance and polymorphism– These two traits are required for a true object-

oriented language