IsPrime

using System;

class isPrime
{
    //second
    static bool IsPrimeTwo(int num)
    {
        if ((num & 1) == 0)
            return num == 2;
        if (num < 9)
            return num > 1;

        for (int i = 3; i < num; i += 2)
        {
            if (num % i == 0)
                return false;
        }

        return true;
    }

    static void Main()
    {
        Console.Write("Enter a number: ");
        sbyte num = sbyte.Parse(Console.ReadLine());

        //first
        bool isPrime = ((num % 2 != 0) && (num % 3 != 0) && (num % 5 != 0) && (num % 7 != 0) && (num != 1));
        bool primeCases = ((num == 2) || (num == 3) || (num == 5) || (num == 7));
        Console.WriteLine((isPrime || primeCases == true) ? "{0} is prime." : "{0} is not prime.", num);

        //second
        Console.WriteLine((IsPrimeTwo(num) == true) ? "{0} is prime." : "{0} is not prime.", num);
    }
}