using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace OperationsAndExpresionsHomework
{
    class IsPrime
    {
        static void Main(string[] args)
        {
            Console.Write("Enter a number: ");
            byte number = byte.Parse(Console.ReadLine());

            if (number==0 || number==1)
            {
                Console.WriteLine("{0} is neither prime, neither composite.", number);
                return;

            }
            else
            {
                Console.Write("Is {0} prime? ", number);
                Console.WriteLine(IsNumberPrime(number) ? " Yes" : " No");
            }


        }

        //Using "byte" because condition for the checked number is: <=100
        static bool IsNumberPrime(byte number)
        {

            if (number % 2 == 0)
            {
                /* Number 2 is also prime. If number is 2, true is returned.
                Else false is returned, because even numbers are not prime.*/
                return number == 2;
            }
            else
            {
                int sqrtOfNumber = (int)Math.Sqrt(number);

                for (int divider = 3; divider <= sqrtOfNumber; divider += 2)
                {
                    if (number % divider == 0)
                    {
                        return false;
                    }
                }
                return true;
            }
        }
    }
}