Create DLL
// C:\> csc /target:module Test.cs namespace CSharpVBInterface { using System; public class Test { public Test() {} public int DaysInMonth( string monName ) { if ( monName == "September" || monName == "April" || monName == "June" || monName == "November" ) return 30; if ( monName == "February" ) return 28; return 31; } public string DayName( int dayNo ) { switch ( dayNo ) { case 0: return "Sunday"; case 1: return "Monday"; case 2: return "Tuesday"; case 3: return "Wednesday"; case 4: return "Thursday"; case 5: return "Friday"; case 6: return "Saturday"; } return "Unknown"; } } }