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  2. 2. INTRODUCTION  C was introduced by “Dennis M ritche” in 1978.  C is a structured programming language.  C is portable language this means that C programs written for one computer can be run on another computer with little modification or no modification.  Another important feature of C is its ability to extend.
  3. 3.  C program is basically collection of functions that are supported by C library. We can continuously add our own functions to C library.  The C compiler combines the capabilities of an assembly language with the features of a high-level language.  Programs written in c are efficient and fast. This is due to its variety of data types and powerful operators.
  4. 4.  Sample C program: main() { /*…………….. printing begins………………*/ printf (“Hello how r u?”); /* ……………………printing ends……………….*/ }  Output of the program is : Hello how r u?  Main() is a special function used by C to tell the compiler where the program starts.  Every program must have exactly one main function.
  5. 5.  If we use morethan one main function, compiler cannot understand which one marks beginning of the program.  The empty pair of parentheses followed by main function indicates that the function has no arguments.  The opening brace “ { ” marks the beginning of the main function and closing brace “}” indicates end of the function.  All statements between “{ ” and “}” these braces form function body.  Function body contains set of instructions to perform the given tasks.
  6. 6.  The function body contains 3 statements out of which only the printf line is an executable statement.  The lines beginning with /* and ending with */are known as comment lines.  Comment lines are not executable statements.  A C program can be viewed as a group of building blocks called functions.  A function is a subroutine that may include one or more statements designed to perform a specific tasks.
  7. 7. AN OVERVIEW OF C PROGRAM A C program consists of following sections: a) Documentation section b) Link section c) Definition section d) Global declaration section e) main function section e) subprogram section  2) Main function consists of 2 parts namely: Declaration part and Executable part  Subprogram section contains all the user defined functions.  1)
  8. 8. Documentation section Link section Definition section Global declaration section main() function section { Declaration part Executable part } Sub program section Function 1 Function 2 user defined function …. Function n
  9. 9.  Documentation section consists of a set of comment lines giving the name of the program, the author and other details which programmer would like to use later.  Link section provides instructions to the compiler to link function from the system library.  Definition section defines all symbolic constants.  Every C program must have one main() function section.  The section contains 2 parts declaration part and executable part.
  10. 10.  Declaration part declares all variables used in executable part.  The 2 parts must appear between opening and closing braces.  All statements in declaration and executable parts end with semicolon (;).  The subprogram section contains all the user-defined functions that are called in main function.  User-defined functions are generally placed immediately after main function, although they may appear in any order.
  11. 11. EXECUTING A C PROGRAM  Executing a program written in C involves a series of steps.  These are 4 steps involved in executing a C program: Creating the program. Compiling the program. Linking the program with functions that are needed from the C library. Executing the program. 1) 2) 3) 4)