isPrime

using System;

//Write an expression that checks if given positive integer number n (n ≤ 100) is prime (i.e. it is divisible without remainder only to itself and 1). Examples:
//n     Prime?
//1     false
//2     true
//3     true
//4     false
//9     false
//97    true
//51    false
//-3    false
//0     false

class PrimeNumberCheck
{
    static void Main()
    {
        Console.Write("Enter a number (n <= 100): ");
        int userInput = int.Parse(Console.ReadLine());
        int upperLimit = (int)Math.Sqrt(userInput);
        bool isPrime = true;

        if (userInput > 0 && userInput != 1) {
            for (int i = 2; i < upperLimit; i++)
            {
                if (userInput % i == 0)
                {
                    isPrime = false;
                    break;
                }
                else
                {
                    isPrime = true;
                }
            }
        }
        else if (userInput == 1)
        {
            isPrime = false;
        }
        else
        {
            isPrime = false;
        }

        Console.WriteLine(isPrime == true ? true : false);
    }
}