C Programs

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Functions in C

Function to multiply two numbers

Introduction

Functions in C help organize programs into smaller, reusable modules.
This program demonstrates how to multiply two numbers using a user-defined function.
The multiplication logic is written inside a function that takes two arguments and returns the product to the main function.

C Program: Function to multiply two numbers

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

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

 
OUTPUT :
Enter first number: 8
Enter second number: 6
Product of 8 and 6 is: 48

Description

1. Function Declaration:
   int multiply(int a, int b); declares a function that accepts two integers and returns an integer.
2. Function Definition:
   Performs multiplication and returns the product.
3. Function Call:
   The function is called from main() with two arguments, and the returned value is stored in product.
4. Output Display:
   The result is printed using printf().

C Program: Function to multiply two numbers

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

#include <stdio.h>
 
// Function declaration
void multiplyNumbers(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
    multiplyNumbers(num1, num2);
 
    return 0;
}
 
// Function definition
void multiplyNumbers(int a, int b) {
    int product = a * b;
    printf("Product of %d and %d is: %d\n", a, b, product);
}

 
OUTPUT :
Enter first number: 9
Enter second number: 7
Product of 9 and 7 is: 63

Description

1. Function Declaration:
   void multiplyNumbers(int a, int b); — defines a function that accepts two integers and has no return type (void).
2. Function Definition:
   • The multiplication is done inside the function.
   • The product is displayed directly using printf().
3. Function Call:
   The function is called from main() with two integer values as arguments.
4. No Return Value:
   The result is printed directly; no value is returned to the main function.