c++

Why doesn't this work
#include <iostream>
#include <string>
int main()
{
   using namespace std;
   unsigned long long int i, num, factor;

    i = 600851475143;

    for (num = 0; num < 10000; num++)
    {
        if (i % num == 0)
        {
            cout << num;
        }

    }
    return 0;
}

>>8
Integers are always promoted to binary doubles so they can be checked.