using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        string str = "Test 123";

        var regx = new Regex("[^a-z A-Z 0-9_.]"); 

        Console.WriteLine("String Value For Null is " + Convert.ToString(null));

        if (regx.IsMatch(str))

        {

            Console.WriteLine("Special character(s) detected.");

        }

        else

        {

            Console.WriteLine("No Special character(s) detected.");

        }

    }

}