#include <iostream>
using namespace std;

bool isaprime(long);

bool isaprime(long x)
{   long n;
    // is 2 a divisor?
    if ( x%2 == 0)
       return false;
    n = 3;
    while (n*n <=x)
    {   if (x%n == 0)
           return false;
        n += 2;
    }
    return true;
}

int main()
{   long x;
    while (1)
    {   cout <<"Enter a positive integer to check for primality, 0 to exit: ";
        cin >> x;
        if (x == 0)
        {   cout << "Thanks for the fun. Come again.\n";
            return 1;
        }
        if (isaprime(x))
           cout <<x<<" is a prime\n";
        else
           cout <<x<<" is not a prime\n";

   }

}