public class Prime {

    public static void main(String[] args) {

        testIsPrime(2);
        testIsNotPrime(6);
        testIsNotPrime(4);
        testIsNotPrime(1);
        testIsPrime(13);
        testIsNotPrime(10);
        testIsNotPrime(16);

    }

    // Precondition: x is an integer > 0
    // Postcondition: the result is true iff x is prime
    public static boolean isPrime(int x) {

        if (x == 1) {
            return false;
        }

        for (int d = 2; d < x; d++) {
            if (x % d == 0) {
                return false;
            }
        }

        return true;
    }

    private static void testIsPrime(int x) {
        if (!isPrime(x)) {
            System.out.println(x + " should be prime, but isPrime says it isn't");
        }
    }


    private static void testIsNotPrime(int x) {
        if (isPrime(x)) {
            System.out.println(x + " should be not prime, but isPrime says it is");
        }
    }


}