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Function in C

A set of statements written to perform any task is known as function.

Syntax –


In above example function, printNaturalNumber has

— set of statements to perform the printing of natural number.

— void input i.e no input parameter.

— void output i.e no output return.

Advantages of Function use

— Function’s use increases the program readability.

— Function’s use decreases the complexity.


A Program without use of function
A Program with use of function

So we can see in above example program is more readable and less complex with the use of functions.

Types of a function

In C language there are two types of function –

— Library defined functions

— User-defined function

Library defined functions

library defined functions are standard functions defined in the standard C library. We only need to include the header file prior to use of any standard function because header file contains the prototype of stnadard C functions.


the main function is defined in the standard library and its prototype declared in stdio.h header file.

printf() ,scanf(), getch(), gets() etc. all functions are standard and defined in a standard library.

User-defined function

User-defined function as the name appears –“A function defined by a user/programmer”. these functions are not standard and these are the project-specific functions written by a programmer to make program modular and less complex.

Above function is an user-defined function written by a programmer to print natural number.