// prime.cpp
// Test if user number is prime

#include <iostream>

using namespace std;

bool is_prime (int);


int main () {

  int num;
  do {
    cout << "Enter a number to test if it's prime (negative number to quit): ";
    cin >> num;
    if (num > 0)
      if (is_prime(num))
        cout << "It's prime" << endl;
      else
        cout << "It's not prime" << endl;
  } while (num > 0);
}



//*****************************************
bool is_prime (int num) {

  int i;

  for (i=2; i<num; i++)
    if (num%i == 0)
      return false;	  // evenly divisible

  return true;
}