Program to Check if Two Numbers are a Friendly Pair in C

Friendly Pair

A friendly pair (also called an amicable pair) is a pair of numbers where the sum of their proper divisors divided by the number itself results in the same value for both numbers. For example, (220, 284) is a friendly pair.

We will explore a method to check if a given pair of numbers is a friendly pair using C programming.

Method: Using a Function

We calculate the sum of proper divisors for both numbers and check if their ratios match.

#include <stdio.h>

int sumOfDivisors(int num) {
    int sum = 0;
    for (int i = 1; i <= num / 2; i++) {
        if (num % i == 0) {
            sum += i;
        }
    }
    return sum;
}

int main() {
    int num1, num2;
    printf("Enter two numbers: ");
    scanf("%d %d", &num1, &num2);
    
    int sum1 = sumOfDivisors(num1);
    int sum2 = sumOfDivisors(num2);
    
    if ((float)sum1 / num1 == (float)sum2 / num2)
        printf("%d and %d are a Friendly Pair", num1, num2);
    else
        printf("%d and %d are not a Friendly Pair", num1, num2);
    
    return 0;
}
            

Output:

Enter two numbers: 220 284
220 and 284 are a Friendly Pair