Program to find all perfect numbers upto n

 An integer is said to be perfect number if its factors (including 1 but not number itself ) is sum to the number

Example:
6 is a perfect number as
6 = 1+2+3

 Program:

/*                       cpp program to find perfect numbers upto n                         */

#include"iostream"

using namespace std;

int main()
{

    int num, i, j, sum = 0;
    do
    {
        cout<<"Enter a number: ";      //get a number upto which perfect number is to be found
        cin>>num;
   
        if(num<1)
        {
            cout<<"Enter a valid positive integer."<<endl;
       
        }
    }while(num<1);

    cout<<"Perfect numbers below "<<num<<" are:"<<endl;
    for(i=1; i<=num; i++)
    {
        sum = 0;
        for(j=1; j<i; j++)       
        {
            if(i%j == 0)
            {
                sum = sum + j;        //sum of factors of i
            }
        }
        if(sum == i)
        {
            cout<<sum<<" = ";
            for(j=1; j<sum; j++)
            {
                if(sum % j == 0)
                {
                    cout<<j<<" ";
                }
            }
            cout<<"\n";
           
        }

    }
   
}

Output: