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C Programming

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C - Basic Introduction

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 Equipment 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 Institute (ANSI).
 By 1973 UNIX OS was 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 adopted 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


C Compilers
When you write any program in C language then to run that program you need to compile that program using a C Compiler which converts your program into a language understandable by a computer. This is called machine language (i.e. binary format). So before proceeding, make sure you have C Compiler available at your computer. Some examples of C compilers are Turbo C and Borland C.

C - Program Structure
A C program basically has the following form:
Preprocessor Commands
Functions
Variables
Statements & Expressions
Comments

Preprocessor Commands: This command tells the compiler to do preprocessing before doing actual compilation. Like;
    #include stdio.h
is a preprocessor command which tells a C compiler to include stdio.h file before going to actual compilation. You will learn more about C Preprocessors in C Preprocessors session. Functions: are main building blocks of any C Program. Every C Program will have one or more functions and there is one mandatory function which is called main() function. This function is prefixed with keyword int which means this function returns an integer value when it exits. This integer value is retured using return statement.
The C Programming language provides a set of built-in functions. printf() is a C built-in function which is used to print anything on the screen.

Variables: Variables are used to hold numbers, strings and complex data for manipulation. Statements & Expressions: Expressions combine variables and constants to create new values. Statements are expressions, assignments, function calls, or control flow statements which make up C programs.

Comments: are used to give additional useful information inside a C Program. All the comments will be put inside /*...*/ as given in the example above. A comment can span through multiple lines.
Note the followings

 C is a case sensitive programming language. It means in C printf and Printf will have different meanings.
 C has a free-form line structure. End of each C statement must be marked with a semicolon.
 Multiple statements can be one the same line.
 White Spaces (ie tab space and space bar ) are ignored.
 Statements can continue over multiple lines.

Data Types in C
A C language programmer has to tell the system before-hand, the type of numbers or characters he is using in his program. These are data types. There are many data types in C language. A C programmer has to use appropriate data type as per his requirement in the program he is going to do.

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