using System;

public class Program

{

    public static void Main()

    {

        string a="Deneme yazısı";

        Console.WriteLine(a.WordCount());

    }

}

​

​

​

    public static class MyExtensions

    {

        public static int WordCount(this String str)

        {

            return str.Split(new char[] { ' ', '.', '?' },

                             StringSplitOptions.RemoveEmptyEntries).Length;

        }

    }