isPrime function that returns 4 as a prime

bool isPrime( int num ) {
    bool prime = true;// Assume it is a prime

    for ( int divisor = 2; divisor < num / 2; divisor++ )
        if ( num % divisor == 0 )
            prime = false;// Not a prime since it's dividable by something.

    return prime;// Return the result
}