Introduction-3

C is a general-purpose high level language that was originally developed by Dennis Ritchie for the Unix operating system. It was first implemented on the Digital Eqquipment Corporation PDP-11 computer in 1972.
The Unix operating system and virtually all Unix applications are written in the C language.


C has now become a widely used professional language for various reasons.
Easy to learn
Structured language
It produces efficient programs.
It can handle low-level activities.
It can be compiled on a variety of computers.


Facts about C
C was invented to write an operating system called UNIX.
C is a successor of B language which was introduced around 1970
The language was formalized in 1988 by the American National Standard Institue (ANSI).
By 1973 UNIX OS almost totally written in C.
Today C is the most widely used System Programming Language.
Most of the state of the art software have been implemented using C


Why to use C ?
C was initially used for system development work, in particular the programs that make-up the operating system. C was adoped as a system development language because it produces code that runs nearly as fast as code written in assembly language. Some examples of the use of C might be:
Operating Systems
Language Compilers
Assemblers
Text Editors
Print Spoolers
Network Drivers
Modern Programs
Data Bases
Language Interpreters
Utilities

Points to be remembered while writing a "C" Program

1.Every C-Program must have atleast one function called main( ). It indicates the starting of the program.


2.All the C statements should be enclosed between a pair of braces left brace ( { ) & right brace( } ).


3.All the C statements should be in lower case letters only.


4.Every statement should be ended with a semicolon.


5.Blank spaces are provided between two words however no blank spaces are allowed within a word. 

Introduction-2

The original PDP-11 version of the Unix system was developed in assembly language. In 1973, C language had become powerful enough that most of the Unix kernel was rewritten in C. This was one of the first operating system kernels implemented in a language other than assembly.


During the rest of the 1970's, C spread throughout many colleges and universities because of its close ties to UNIX and the availability of C compilers. Soon, many different organizations began using their own versions of C Language. This was causing great compatibility problems. In 1983, the American National Standards Institute (ANSI) formed a committee to establish a standard definition of C Language. That is known as ANSI Standard C. Today C is the most widely used System Programming Language.

Introduction

C was developed by Dennis Ritchie at Bell Laboratories in 1972. 
Most of its principles and ideas were taken from the earlier language B, BCPL and CPL. CPL was developed jointly between the Mathematical Laboratory at the University of Cambridge and the University of London Computer Unit in 1960s. 
CPL (Combined Programming Language) was developed with the purpose of creating a language that was capable of both machine independent programming and would allow the programmer to control the behavior of individual bits of information.

But the CPL was too large for use in many applications. 
In 1967, BCPL (Basic Combined Programming Language) was created as a scaled down version of CPL while still retaining its basic features. This process was continued by Ken Thompson. 
Ken Thompson made B Language during working at Bell Labs. B Language was a scaled down version of BCPL. B Language was written for the systems programming.
In 1972, a co-worker of Ken Thompson, Dennis Ritchie developed C Language by taking some of the generality found in BCPL to the B language.