Is Integer Number Prime

using System;
class IsIntNumPrime
{
  static void Main()
  {
    //Write an expression that checks if given positive integer number n (n ≤ 100) is prime. E.g. 37 is prime.

    Console.Write("Enter an integer number between 0 and 100:");
    int numberToCheck = int.Parse(Console.ReadLine());
    bool isPrime = true;
    if (numberToCheck < 0 || numberToCheck > 100)
      Console.WriteLine("Wrong input! The integer number should be between 0 and 100!");
    else
    {
      for (int index = 2; index <= (int)Math.Sqrt(numberToCheck); index++)
      {
        int buffernumber = (numberToCheck % index);
        if (buffernumber == 0)
          isPrime = false;
        else break;
      }
      Console.WriteLine("The number {0} {1} prime!", numberToCheck, (isPrime == true) ? "is" : "isn't");
    }
  }
}