C Foundation

What is C? C Compiler Installation C Extensions C Compiler C Interpreter C Program Structure

C Basics

C Keywords C Data Types C Identifiers C Variables C Constant C Escape Sequences C Constant and Volatile C Typecast


What is Operator C Comma Operator C Arithmetic Operators C Relational Operators C Logical Operators C Bitwise Operators C Conditional Operators C : : Operator C Operator Priority

Basic IO's

Basic IO's C Formatted Functions C Unformatted Functions C Common Functions

Control Statements

What is Control Statement C if Statement C if else Statement C Nested if Statement C Else if Statement C Break Statement C Continue Statement C Switch Statement C Goto Statement


What is Control Loop C for Loop C Nested for Loop C while Loop C Nested while Loop C do while Loop C Nested do while loop


What is Function C User Defined Functions C Recursion C Passing Parameters


Scope C Local Scope C Global Scope

Storage Classes

What is Storage Class C Auto C Extern C Static C Register


What is Array C One Dimensional Array C Two Dimensional Array C Multi Dimensional Array C Arrays Of Strings


What is String C String Functions


What is Pointer C Pointers Arithmetic C Pointer to Pointer C Pointers and Arrays C Pointers and Strings C Pointer to Functions Void Pointers Null Pointers C Null and Void Pointer


What is Structure C Struct within Struct C Array within Structure C Pointer to Structure C Structure and Function C Enum C Bitfield Structure C Type def


What is Union


What is File C read a file C write a file C File Handling C Error Handling C Low Level Disk I/O C Other file functions

Memory Allocation

What is Memory Allocation C Malloc() C Calloc() C Free() C Realloc() C Coreleft()

C Reference

All ASCII Code Basic C Questions

C Interview

C Interview Sets All Star Patterns All Number Patterns All Alphabet Patterns All Series Patterns
The ones who are crazy enough to think they can change the world are the ones who do.
- Steve Jobs

C Functions

What Is a Function?

In general terms, a function is also called a subroutine in some other languages like php, python and so on. Function is a self contained block of code that performs a specific task. A programmer define a function using its predefined syntax, a programmer can then call that function from elsewhere in your program.

C Functions

Why Function?

  • They avoid duplicating codes.
  • They make it easier to eliminate errors.
  • Function help you break down a big project.

Function and Arguments

A function often accepts none, one or more arguments, which are values passed to the function by the code that calls it. The function is capable of read and work on those arguments. A function may also optionally return a value(non void type) that can then be read by the calling code. in this way, the calling code will communicate with the function.

How Program thinks?

Program think of a function as a black box. The code that calls a function doesn't need to know what's inside the function, it just uses the function to get the job done.


return-type function-name (arguments); 
statements within main function; 
printf("%d", function-name (arguments));    //function call
return-type function-name (arguments)      //function definition
statements within user-defined function;
return variablename;

Types Of Function

There are two types of functions they are,

  • Library Functions
  • User Defined functions

Library Functions

C provides many pre-defined functions to perform a task, those functions are defined in an appropriate header files.

  • printf()
  • scanf()
  • strlen()
  • sqrt() and so on

User Defined Functions

C allows users or programmers to define a function according to their requirement. The main() function is also a user-defined function because the statements inside the main function is defined by the user, only the function name is defined in a library.

Function Declaration

  • The function declaration statement informs the compiler about a function return type, function name and parameters or arguments type.
  • Syntax : return-type function-name (arguments);
  • Return type : return type is the data type of the value which is given back to the calling function.
  • function name : function name is the name of a function. A function is called by using the function name. The naming rules are same as variable naming.
  • parameters or arguments type : C allows programmers to pass information to the called function from the calling function by using parameters. These parameters are variables of data type.

C program - Functions

The following example program will clearly explain the concept of functions

#include <stdio.h>
int main()
//main function definition
int a = 5, b = 10;
int sum;
printf("The value of a and b : %d %d ", a, b);
sum = add(a, b);    //function call
printf("\nsum = %d ", sum);
//function definition
int add(int a, int b)
int c;
c = a + b;
return c;    //returns a integer value to the calling function
  • The value of a and b : 5 10
  • sum = 15


The above C program illustrates that a function declaration, function definition and function call in a program.

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