C Functions

C function is a self-contained block of statements that can be executed repeatedly whenever we need it.

Benefits of using the function in C

  • The function provides modularity.
  • The function provides reusable code.
  • In large programs, debugging and editing tasks is easy with the use of functions.
  • The program can be modularized into smaller parts.
  • Separate function independently can be developed according to the needs.

There are two types of functions in C

  • Built-in(Library) Functions
    • The system provided these functions and stored in the library. Therefore it is also called Library Functions.
      e.g. scanf(), printf(), strcpy, strlwr, strcmp, strlen, strcat etc.
    • To use these functions, you just need to include the appropriate C header files.
  • User Defined Functions These functions are defined by the user at the time of writing the program.

Parts of Function

  1. Function Prototype (function declaration)
  2. Function Definition
  3. Function Call

1. Function Prototype

dataType functionName (Parameter List)
int addition();

2. Function Definition

returnType functionName(Function arguments){
  //body of the function 
int addition()


3. Calling a function in C

Program to illustrate the Addition of Two Numbers using User Defined Function


/* function declaration */int addition();

int main()
    //local variable definition
    int answer;
    answer = addition(); //calling a function to get addition value.
    printf("The addition of the two numbers is: %d\n",answer);
    return 0;

//function returning the addition of two numbers
int addition()
    int num1 = 10, num2 = 5; // local variable definition
    return num1+num2;
Program Output:

The addition of the two numbers is: 15

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