Types of Functions in C Programming

C program has two types of functions:

1. Library Functions

2. User defined functions

Library Functions:

These are the functions which are already written, compiled and placed in C Library and they are not required to be written by a programmer. The function’s name, its return type, their argument number and types have been already defined. We can use these functions as required. For example: printf(), scanf(), sqrt(), getch(), etc.

User defined Functions:

These are the functions which are defined by user at the time of writing a program. The user has choice to choose its name, return type, arguments and their types. The job of each user defined function is as defined by the user. A complex C program can be divided into a number of user defined functions.

For example:

#inlcude<stdio.h>

double convert (int) ; /* function proto type */

main()

{ int c ;

/* double d ; */

printf (“Enter temperature in Celsius: ”) ;

scanf (“%d”, &c) ;

/* d = convert(c) ; */ /*Function call*/

printf (“The Fahrenheit temperature of %d C = $lf F”;c, convert (c) ;

/* d inplace of convert */

}

double convert (int C) /* function definition */

{

double f ;

f = 9.0*c/5.0+32.0 ;

return f ;

}

What is about main( ) function?

The function main() is an user defined function except that the name of function is defined or fixed by the language. The return type, argument and body of the function are defined by the programmer as required. This function is executed first, when the program starts execution.