C#

<br />
using System;<br />
   [AttributeUsage(AttributeTargets.Method|AttributeTargets.Struct]<br />
   public class MyAttribute:Attribute<br />
   {<br />
      private string regKey="abc";<br />
      public MyAttribute(string regKey)<br />
      {<br />
         if(this.regKey==regKey)<br />
         {<br />
            Console.WriteLine("Permitted to use this App");<br />
         }<br />
         else<br />
         {<br />
            Console.WriteLine("Not registered to use this App");<br />
         }<br />
      }<br />
   }    //End Attribute class code<br />
   class useAttrib<br />
   {<br />
      [MyAttribute("hello")]<br />
      public static string SayHello(string str)<br />
      {<br />
         return str;<br />
      }<br />
      static void Main()<br />
      {<br />
         Console.WriteLine(SayHello("Hello to Sufyan"));<br />
         Console.ReadLine();<br />
      }<br />
   }<br />