Number is a perfect number or not

Posted on Apr 8, 2020

C program to check whether a given number is a perfect number or not.

A perfect number is a positive integer that is equal to the sum of its positive divisors, excluding the number itself.

For example, num = 28
Divisors of 28: 1, 2, 4, 7, 14, 28
Sum of divisors (excluding 28): 1 + 2 + 4 + 7 + 14 = 28
Sum = Original number
So, 28 is a perfect number

Some of the perfect numbers are 6, 28, 496, 8128, and 33550336, etc.

Program 

#include<stdio.h>
#include<conio.h>
void main()
{
	int num, i, sum;

    printf("Enter the number\t:");
    scanf("%d",&num);
    sum = 0;
    printf("The positive divisors  are ");
    for(i=1;i<num;i++)
    {
        if(num%i==0)
        {
            sum=sum+i;
            printf("%d  ",i);
        }
    }
    printf("\nThe sum of the divisors is : %d",sum);
    if(sum==num)
        printf("\nSo, the number is perfect.");
    else
        printf("\nSo, the number is not perfect.");

    getch();
}

Output 

********** Run1 **********

Enter the number        :56
The positive divisors  are 1  2  4  7  8  14  28
The sum of the divisors is : 64
So, the number is not perfect.



********** Run2 **********

Enter the number        :496
The positive divisors  are 1  2  4  8  16  31  62  124  248
The sum of the divisors is : 496
So, the number is perfect.