PROGRAMMING LANGUAGES

PROGRAMMING LANGUAGES

Programming languages fall in three broad categories:

1.    Machine Language

2.    Assembly Language

3.    High Level Language

1.      Machine Language

The first-generation programming language, or 1GL, is machine code. It is sometimes referred to as machine code or object code, machine language.It is a collection of binary digits or bits that the computer reads and interprets. Machine language can be directly understood and obeyed by a machine (computer) without conversion (translation). Hence, Machine languages are the only languages understood by computers.

Each type of computer has its own machine language which consists of zeros and ones. Program written in machine language for one computer will not work on another because of design difference. While easily understood by computers, machine languages are almost impossible for humans to use because they consist entirely of numbers. Programmers, therefore, use either a high-level programming language or an assembly language.

For a machine language, each unique combination of 1's and 0's in an instruction has a unique interpretation, including such operations as arithmetical operations, incrementing a counter, saving data to memory, testing if data has a certain value, and so on.

2.    Assembly Language

The second-generation programming language, or 2GL, is assembly language. An assembly language allows the programmer to use all the computer features through symbolic codes and locations rather than machine codes and binary. Before an assembly language program can be run on a computer, it must be converted to machine language using a special program called assembler.

A program prepared in assembly language will require less storage and less running time than one prepared in a high level language; an equivalent program in a high-level language will be more heavyweight. Low-level languages are simple, but are considered difficult to use, due to the numerous technical details which must be remembered. Assembly language is much harder to program than high level languages.

Machine languages are one to one correspondence between language mnemonics and executable machine instructions. In assembly language, one symbolic instruction must be written for each machine langue instruction, however several lines of assembly language are needed to encode one line of a high-level language program.

3.    High Level Language(HLL)

A HLL is much more powerful programming tool than an assembly language. High level languages are English oriented language. In assembly language, one symbolic instruction must be written for each machine langue instruction, but in a high level language, one statement will produce a multitude of machine language instruction.

A special program known as compiler is used for translating a high level language program in to its machine language equivalent program.

Another difference between assembly language and high level language is that it is impossible to use the assembly language of one computer on any other computer. This is not the case with high level languages which are considered problem oriented rather than machine oriented.

One of the first HLLs was FORTRAN which stands for FORmula TRANslation. It was developed for the IBM 704 by John Backus and a team of thirteen other programmers at IBM over a three year period (1954-1957). It was designed to write programs for solving scientific and engineering problems.

COBOL stands for Common Business Oriented Language. It was developed in 1959 for solving business computing. It has been used very successfully for writing programs such as accounting, payroll and inventory control.

The major advantages of high-level languages are that they are easy to read and are machine independent. The instructions are written in a combination of English and ordinary mathematical notation.

Programmers commonly use more English-like languages (called high level languages) such as Basic, C, Java, etc., to write programs which are then translated into machine language (called a low level language) by an assembler, compiler, or interpreter.

BASIC STRUCTURE OF A C PROGRAM

To introduce the structure of a C program, consider the following simple program that will print the message:

I love pakistan

The program may be written as follows:

#include<stdio.h>

#include<conio.h>

void main()

{

printf(“I Love Pakistan”);

getch();

}

The # sign indicates that this is an instruction for a compiler. <stdio.h> stands for Standard input output header. One item included in this header is a declaration of the function printf(). A C program consists of one or more functions. A function is a set of statements that performs a single well defined task. A C program cannot run without a main function. Every C program must have the function main () which is the first section to be executed when the program runs. The word void before the function main () means that this function does not return any value and the empty parentheses means it does not have any arguments.

The body of the function is surrounded by curly brackets {and}. The left brace indicates the start of the function and the matching right braces indicates the end of the body of the function.

The body of the function in our program consists of a single statement printf( ) which ends with a semicolon. printf( ) is the standard output function. The text to be printed is enclosed in double quotes. A statement in C is terminated with a semicolon (;).

When the program runs, the string “I Love Pakistan” is printed on the screen.