C Programming Tutorial
About Lesson

C Functions

In this tutorial, you will learn about the C Library functions and return statement with the help of examples.


  • Function is a block of code which is used to performs a specific task.
  • Functions are used to provide modularity & code reusability to a program.
  • The Function is also known as procedure or subroutine in other programming languages.
  • Every C program has at least one function, which is main().
  • Dividing a complex problem into smaller chunks makes our program easy to understand and reusable.

Why do we need Functions?

  • It divides the program into separate well-defined functions so that each function can be written and tested separately.
  • Understanding, coding and testing becomes very easy as they are separated.
  • Writing functions avoids rewriting the same code over and over.
  • As the functions are divided the workload can also be divided among the programmers.

Advantages of Functions

  • It makes the program clear and easy to understand.
  • Single Functions can be tested easily for errors.
  • It saves time from typing th same function again and again.
  • It helps to modify the program easily without changing the structure of a program.
  • Function can be called multiple times as per requirement.

Types of Function

There are two types of functions in C programming:

  1. Standard Library Functions : are the functions which are Predefined in C Language.
  2. User-defined Function : are the functions which are Created by users.

Standard library functions

  • Library functions are the built-in functions in C programming.
  • Library functions are those type of functions which are already defined, compiled and stored in different header files of standard C library.
  • Users can use library functions by calling the functions directly; they don’t need to write the functions themselves.

For example :

Some common library functions in C programming are printf()scanf(), etc.

In order to use mathematical functions such as sqrt() and abs(), we need to
include the header file <math.h>.

Example : Standard Library function

#include <stdio.h>
// declaring "cmath" header file to use mathematical functions
#include <math.h>
int main() {
  int number;
  double squareRoot;
  number = 9;
  // sqrt() is a library function to calculate the square root
  squareRoot = sqrt(number);
  printf("Square root of %d is %lf ",number,squareRoot);
  return 0;


Square root of 9 = 3.000000

In this program, the sqrt() library function is used to calculate the square root of a number.

The function declaration of sqrt() is defined in the math.h header file. That’s why we need to use the code #include <math.h> to use the sqrt() function.

Visit standard library functions in C programming to learn more.

Return Statement

The Return statement is used to terminate the execution of a function and transfer program control back to the calling function.

It can also specify a value to be returned by the function.

Syntax :

void Number() {
  // statement
  • This means the function is not returning any value.
  • It’s also possible to return a value from a function.
  • For this, we need to specify the returnType of the function during function declaration.
  • Then, the return statement can be used to return a value from a function.

For example,

int add (int a, int b) {
  return (a + b);

Here, we have the data type int instead of void. This means that the function returns an int value.

The code return (a + b); returns the sum of the two parameters as the function value.

The return statement denotes that the function has ended. Any code after return inside the function is not executed.

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