Imports System.Globalization

Module Example
   Public Sub Main()
      Dim dateValue As Date = #06/01/2009 4:37PM#
      Dim cultures() As CultureInfo = {New CultureInfo("en-US"), _
                                       New CultureInfo("fr-FR"), _
                                       New CultureInfo("it-IT"), _
                                       New CultureInfo("de-DE") }
      For Each culture As CultureInfo In cultures
         Console.WriteLine("{0}: {1}", culture.Name, dateValue.ToString(culture))
      Next                                        
   End Sub
End Module
' The example displays the following output:
'       en-US: 6/1/2009 4:37:00 PM
'       fr-FR: 01/06/2009 16:37:00
'       it-IT: 01/06/2009 16.37.00
'       de-DE: 01.06.2009 16:37:00

using System;
using System.Globalization;

public class Example
{
   public static void Main()
   {
      DateTime dateValue = new DateTime(2009, 6, 1, 4, 37, 0);
      CultureInfo[] cultures = { new CultureInfo("en-US"), 
                                 new CultureInfo("fr-FR"),
                                 new CultureInfo("it-IT"),
                                 new CultureInfo("de-DE") };
      foreach (CultureInfo culture in cultures)
         Console.WriteLine("{0}: {1}", culture.Name, dateValue.ToString(culture));
   }
}
// The example displays the following output:
//       en-US: 6/1/2009 4:37:00 PM
//       fr-FR: 01/06/2009 16:37:00
//       it-IT: 01/06/2009 16.37.00
//       de-DE: 01.06.2009 16:37:00

Public Class AcctNumberFormat : Implements IFormatProvider, ICustomFormatter

   Private Const ACCT_LENGTH As Integer = 12

   Public Function GetFormat(formatType As Type) As Object _
                   Implements IFormatProvider.GetFormat
      If formatType Is GetType(ICustomFormatter) Then
         Return Me
      Else
         Return Nothing
      End If
   End Function

   Public Function Format(fmt As String, arg As Object, formatProvider As IFormatProvider) As String _
                          Implements ICustomFormatter.Format

      ' Provide default formatting if arg is not an Int64.
       If Not TypeOf arg Is Int64 Then
         Try 
            Return HandleOtherFormats(fmt, arg) 
         Catch e As FormatException 
            Throw New FormatException(String.Format("The format of '{0}' is invalid.", fmt), e)
         End Try
       End If   

      ' Provider default formatting for unsupported format strings.
      Dim ufmt As String = fmt.ToUpper(CultureInfo.InvariantCulture)
      If Not (ufmt = "H" Or ufmt = "I") Then
         Try
            Return HandleOtherFormats(fmt, arg)
         Catch e As FormatException 
            Throw New FormatException(String.Format("The format of '{0}' is invalid.", fmt), e)
         End Try
      End If   

      ' Convert argument to a string.
      Dim result As String = arg.ToString()

      ' If account number is less than 12 characters, pad with leading zeroes.
      If result.Length < ACCT_LENGTH Then result = result.PadLeft(ACCT_LENGTH, "0"c)
      ' If account number is more than 12 characters, truncate to 12 characters.
      If result.Length > ACCT_LENGTH Then result = Left(result, ACCT_LENGTH)   

      If ufmt = "I"                              ' Integer-only format.
         Return result
      ' Add hyphens for H format specifier.
      Else                                       ' Hypenated format.
         Return Left(result, 5) & "-" & Mid(result, 6, 3) & "-" & Right(result, 4)
      End If   
   End Function   

   Private Function HandleOtherFormats(fmt As String, arg As Object) As String
      If TypeOf arg Is IFormattable Then
         Return DirectCast(arg, IFormattable).ToString(fmt, CultureInfo.CurrentCulture)
      ElseIf arg IsNot Nothing Then
         Return arg.ToString()
      Else
         Return String.Empty
      End If
   End Function
End Class

public class AcctNumberFormat : IFormatProvider, ICustomFormatter
{
   private const int ACCT_LENGTH = 12;

   public object GetFormat(Type formatType)
   {
      if (formatType == typeof(ICustomFormatter))
         return this;
      else
         return null;
   }

   public string Format(string fmt, object arg, IFormatProvider formatProvider) 
   {
      // Provide default formatting if arg is not an Int64.
      if (arg.GetType() != typeof(Int64))
         try {
            return HandleOtherFormats(fmt, arg); 
         }
         catch (FormatException e) {
            throw new FormatException(String.Format("The format of '{0}' is invalid.", fmt), e);
         }

      // Provide default formatting for unsupported format strings.
      string ufmt = fmt.ToUpper(CultureInfo.InvariantCulture);
      if (! (ufmt == "H" || ufmt == "I")) 
         try {
            return HandleOtherFormats(fmt, arg);
         }
         catch (FormatException e) {
            throw new FormatException(String.Format("The format of '{0}' is invalid.", fmt), e);
         }

      // Convert argument to a string.
      string result = arg.ToString();

      // If account number is less than 12 characters, pad with leading zeroes.
      if (result.Length < ACCT_LENGTH)
         result = result.PadLeft(ACCT_LENGTH, '0');
      // If account number is more than 12 characters, truncate to 12 characters.
      if (result.Length > ACCT_LENGTH)
         result = result.Substring(0, ACCT_LENGTH);   

      if (ufmt == "I")                    // Integer-only format. 
         return result;
      // Add hyphens for H format specifier.
      else                                         // Hyphenated format.
         return result.Substring(0, 5) + "-" + result.Substring(5, 3) + "-" + result.Substring(8);
   }

   private string HandleOtherFormats(string format, object arg)
   {
      if (arg is IFormattable) 
         return ((IFormattable)arg).ToString(format, CultureInfo.CurrentCulture);
      else if (arg != null)
         return arg.ToString();
      else
         return String.Empty;
   }
}

Imports System.Globalization

Public Enum DaysOfWeek As Long
   Monday = 1
   Tuesday = 2
End Enum

Module TestFormatting
   Public Sub Main()
      Dim acctNumber As Long, balance As Double 
      Dim wday As DaysOfWeek 
      Dim output As String

      acctNumber = 104254567890
      balance = 16.34
      wday = DaysOfWeek.Monday

      output = String.Format(New AcctNumberFormat(), "On {2}, the balance of account {0:H} was {1:C2}.", acctNumber, balance, wday)
      Console.WriteLine(output)

      wday = DaysOfWeek.Tuesday
      output = String.Format(New AcctNumberFormat(), "On {2}, the balance of account {0:I} was {1:C2}.", acctNumber, balance, wday)
      Console.WriteLine(output)
   End Sub
End Module
' The example displays the following output:
'    On Monday, the balance of account 10425-456-7890 was $16.34.
'    On Tuesday, the balance of account 104254567890 was $16.34.

using System;
using System.Globalization;

public enum DaysOfWeek { Monday=1, Tuesday=2 };

public class TestFormatting
{
   public static void Main()
   {
      long acctNumber;
      double balance; 
      DaysOfWeek wday; 
      string output;

      acctNumber = 104254567890;
      balance = 16.34;
      wday = DaysOfWeek.Monday;

      output = String.Format(new AcctNumberFormat(), 
                             "On {2}, the balance of account {0:H} was {1:C2}.", 
                             acctNumber, balance, wday);
      Console.WriteLine(output);

      wday = DaysOfWeek.Tuesday;
      output = String.Format(new AcctNumberFormat(), 
                             "On {2}, the balance of account {0:I} was {1:C2}.", 
                             acctNumber, balance, wday);
      Console.WriteLine(output);
   }
}
// The example displays the following output:
//       On Monday, the balance of account 10425-456-7890 was $16.34.
//       On Tuesday, the balance of account 104254567890 was $16.34.