User defined Function in C programming

A function is a self-contained block of statements which we can use whenever we want. A user-defined function is a type of function which is defined by the user.

Types of user-defined function in C

• Function with no arguments and no return value.
• Function with arguments and no return value.
• Function with no arguments and a return value.
• Function with arguments and a return value.

Type 1: Function with no arguments and no return value.

// example of a void function with no arguments.

#include <stdio.h>

void Add()
{
    int a, b;               // declaring variables.
    scanf("%d %d",&a, &b);  // taking input from user.
    
    int sum = a + b;        // storing the summation of given two numbers.
    printf("Summation of given two numbers = %d \n", sum);
}


int main()
{
    Add(); // calling function from the main.
    return 0;
}

Note

• Above Function has no arguments and no return value. So it is a void function.
• After calling this function from the main, this function will take input from the user and print the sum of two numbers.

Type 2: Function with arguments and no return value.

// This is an example of a void function with arguments.

#include <stdio.h>

void Add(int a, int b)
{
    int sum = a + b;        // storing the summation of given two numbers.
    printf("Summation of given two numbers = %d \n", sum);
}


int main()
{
    int x, y;               // declaring variables.
    scanf("%d %d",&x, &y);  // taking input from user.

    Add(x, y); // calling function from the main.

    return 0;
}

Note

• Above Function has arguments but no return value. So it is also a void function.
• Above function is passing parameters from the main after that, Add function will print the summation of these two numbers.

Type 3: Function with no arguments and a return value.

// This is an example of a no argument function which has a return value.

#include <stdio.h>

int Add()
{
    int a, b;               // declaring variables.
    scanf("%d %d",&a, &b);  // taking input from user.

    int sum = a + b;        // storing the summation of given two numbers.
    return sum;             // return the sum value
}


int main()
{
    int result = Add();  // calling function from the main and receiving the return value.

    printf("Summation of given two numbers = %d \n", result);
    return 0;
}

Note

• When we call the function from the main it will return a value.
• For receiving the return value we used result variable and assigned the Add() function into that variable so that the return data can be stored into the variable called result.
• We can use different names for the variable but the datatype of the must be same as the function return data type.

Type 4: Function with arguments and a return value.

// This is an example of a function which has arguments and a return value also.

#include <stdio.h>

int Add(int a, int b)
{
    int sum = a + b;        // storing the summation of given two numbers.
    return sum;             // return the sum value
}


int main()
{
    int x, y;                // declaring variables.
    scanf("%d %d",&x, &y);   // taking input from user.

    int result = Add(x, y);  // calling function from the main.

    printf("Summation of given two numbers = %d \n", result);
    return 0;
}

Note

• In this case we take input into the main function and passed it through the Add() function which is the only difference from the previous example.

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Structure of a Function in C programming

At that point we should have a good idea on C programming so it is time to move on a topic like Function. What is function? It is little bit difficult to explain in a sentence. We know what is loop and what it does, right? We used loop to execute any block of code several times but what if I want to repeat any block of code at any time/part of our program! Exactly, we can do this using function.

Function is a self contained block of statements which we can use whenever we want. Every Program has at least one function in C programming called ‘main()’.

Structure of a function

return_type  function_name ( parameter_list )
{
     // Function body
}

return_type : return_type is the date type which any function returns in C. Function in C must have a return type.

Functions may or may not return any value. If it does not returns any value then the return_type will be void. void function indicates it returns nothing.

function_name : function_name is simply the name of the function.

parameter_list : Parameters are like placeholder. Any function may have zero or more parameters. Any types of parameters can be used in a function. If there are more than one parameters then every parameter will be separated by a comma.

Types of Function in C

• Standard Library Functions ( ex. scanf(), printf(), etc )
• User Defined Functions

Look at the following example for better understanding

#include <stdio.h>

int add ( int a, int b )
{
    int result = a + b;
    return result; 
}

int main()
{
    int a, b;
    scanf("%d %d",&a, &b);
    
    int sum = add(a, b);   // calling function from main.
    printf("Summation of given two number is %d \n", sum);

    return 0;
}

Note

• Above function has a return value of integer.
• return keyword is used in C to return value from function.
• To use any function in C programming, it must be called from the main function otherwise it won't work.

Advantages of using Function in C

• We can reuse our code at anywhere in our program.
• It makes debugging and editing more easier.
• It makes program more readable.
• It makes code more optimized.

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