code to check whether a number is prime or not.

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

namespace ConsoleApplication20jan
{
    class Class5
    {
        static void Main()
        {
            Console.WriteLine("Enter number : ");
            int n = Convert.ToInt32(Console.ReadLine());
            for (int a = 2; a <= n / 2; a++)
            {
                if (n % a== 0)
                {
                    Console.WriteLine("Number is not prime");
                    return;
                }
            }
            Console.WriteLine("Number is Prime");

        }
    }
}