C Programs

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Functions in C

Function to add two numbers

Introduction

In C programming, functions are used to divide a large program into smaller, manageable parts.
This program demonstrates how to add two numbers using a user-defined function.
The addition logic is placed inside a separate function named add(), which improves modularity and code reusability.

C Program: Function to add two numbers

Method 1: The function with int return type (With Arguments, With Return)

#include <stdio.h>
 
// Function declaration
int add(int a, int b);
 
int main() {
    int num1, num2, sum;
 
    // Taking input from user
    printf("Enter first number: ");
    scanf("%d", &num1);
    printf("Enter second number: ");
    scanf("%d", &num2);
 
    // Function call
    sum = add(num1, num2);
 
    // Display result
    printf("Sum of %d and %d is: %d\n", num1, num2, sum);
 
    return 0;
}
 
// Function definition
int add(int a, int b) {
    return a + b;
}

 
OUTPUT :
Enter first number: 10
Enter second number: 20
Sum of 10 and 20 is: 30

Description

1. Function Declaration:
   int add(int a, int b); tells the compiler that there is a function named add which takes two integers and returns an integer.
2. Function Definition:
   The function add(int a, int b) performs the addition of two integers and returns the result.
3. Function Call:
   The main() function calls add(num1, num2) and stores the result in sum.
4. Output Display:
   The result is printed on the screen using printf().

C Program: Function to add two numbers

Method 2: The function with void return type (With Arguments, No Return)

In this program, we will create a void function that takes two numbers as arguments, adds them, and directly prints the result.

#include <stdio.h>
 
// Function declaration
void addNumbers(int a, int b);
 
int main() {
    int num1, num2;
 
    // Taking input from user
    printf("Enter first number: ");
    scanf("%d", &num1);
    printf("Enter second number: ");
    scanf("%d", &num2);
 
    // Function call
    addNumbers(num1, num2);
 
    return 0;
}
 
// Function definition
void addNumbers(int a, int b) {
    int sum = a + b;
    printf("Sum of %d and %d is: %d\n", a, b, sum);
}

 
OUTPUT :
Enter first number: 15
Enter second number: 25
Sum of 10 and 20 is: 40

Description

1. Function Declaration:
   void addNumbers(int a, int b); tells the compiler that the function does not return a value.
2. Function Definition:
   The function calculates the sum and prints it directly inside the function body.
3. Function Call:
   The main() function calls addNumbers(num1, num2) after reading user input.
4. No Return Value:
   The function performs the task (printing) without returning any result to the caller.