Class extension example

 namespace ConsoleApplication1  
 {  
   public static class MyExtensions  
   {  
     public static int WordCount(this String str)  
     {  
       return str.Split(new char[] { ' ', '.', '?' },  
         StringSplitOptions.RemoveEmptyEntries).Length;  
     }  
   }  
   class Program  
   {  
     static void Main(string[] args)  
     {  
       string s = "1.2.3";  
       Console.WriteLine( s.WordCount().ToString());  
       Console.ReadKey();  
     }  
   }  
 }  

Fancy LINQ operation

   class Myclass  
   {  
     public string name { get; set; }  
     public decimal age { get; set; }  
   }  
   class Program  
   {  
     static void Main(string[] args)  
     {  
       List<string> l = new List<string>();  
       l.Add("di"); l.Add("marks");  
       var list = new List<Myclass> { new Myclass { name = "di",age = 0 }, new Myclass { name = "marks", age = 0 }, new Myclass { name = "grade", age = 0 } };  
       list.Where(w => l.Contains(w.name)).ToList().ForEach(i => i.age = 10);  
       list.ForEach(i => Console.WriteLine(i.name + ":" + i.age));  
       Console.ReadKey();  
     }  
   }