Creating User-Defined Function for Excel

Code:

using System;
using System.Collections.Generic;
using System.Text;

using Microsoft.Office.Excel.Server.Udf;

namespace ExcelSamples
{
   [UdfClass]
   public class MyFirstUDF
   {
      [UdfMethod]
       public Int32 RandomNo()
       {
          Random r = new Random();
          return (Int32)((r.NextDouble()*5)+1);
        }
     }
}

Article:
http://msdn.microsoft.com/en-us/library/bb428649.aspx
http://www.wrox.com/WileyCDA/Section/Excel-Services-User-Defined-Functions-UDFs-.id-305100.html