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
      ' 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)   

      ' Support G and H format specifiers.
      If String.IsNullOrEmpty(fmt) Then fmt = "G"

      If fmt.ToUpper = "G"
         Return result
      ' Add hyphens for H format specifier.
      Else If fmt.ToUpper = "H"
         Return Left(result, 5) & "-" & Mid(result, 6, 3) & "-" & Right(result, 4)
      ' Throw an exception for any other format specifier.
      Else
         Throw New FormatException(String.Format("{0} is not a valid format string.", fmt))
      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) 
   {
      // 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);   

      // Support G and H format specifiers.
      if (String.IsNullOrEmpty(fmt))
         fmt = "G";

      if (fmt.ToUpper() == "G")
         return result;
      // Add hyphens for H format specifier.
      else if (fmt.ToUpper() == "H")
         return result.Substring(0, 5) + "-" + result.Substring(5, 3) + "-" + result.Substring(8);
      // Return string representation of argument for any other formatting code.
      else
         throw new FormatException(String.Format("{0} is not a valid format string.", fmt));
   }
}

Module TestFormatting
   Public Sub Main()
      Dim acctNumber As Long 

      acctNumber = 104254567890
      Console.WriteLine(String.Format(New AcctNumberFormat, "{0:H}", acctNumber))
      Console.WriteLine(String.Format(New AcctNumberFormat, "{0}", acctNumber))
      acctNumber = 14567890
      Console.WriteLine(String.Format(New AcctNumberFormat, "{0:H}", acctNumber))
      Console.WriteLine(String.Format(New AcctNumberFormat, "{0}", acctNumber))
      acctNumber = 18779887654111
      Console.WriteLine(String.Format(New AcctNumberFormat, "{0:H}", acctNumber))
      Console.WriteLine(String.Format(New AcctNumberFormat, "{0}", acctNumber))
   End Sub
End Module
' The example displays the following output:
'       10425-456-7890
'       104254567890
'       00001-456-7890
'       000014567890
'       18779-887-6541
'       187798876541

public class TestFormatting
{
   public static void Main()
   {
      long acctNumber;

      acctNumber = 104254567890;
      Console.WriteLine(String.Format(new AcctNumberFormat(), "{0:H}", acctNumber));
      Console.WriteLine(String.Format(new AcctNumberFormat(), "{0}", acctNumber));
      acctNumber = 14567890;
      Console.WriteLine(String.Format(new AcctNumberFormat(), "{0:H}", acctNumber));
      Console.WriteLine(String.Format(new AcctNumberFormat(), "{0}", acctNumber));
      acctNumber = 18779887654111;
      Console.WriteLine(String.Format(new AcctNumberFormat(), "{0:H}", acctNumber));
      Console.WriteLine(String.Format(new AcctNumberFormat(), "{0}", acctNumber));
   }
}
// The example displays the following output:
//       10425-456-7890
//       104254567890
//       00001-456-7890
//       000014567890
//       18779-887-6541
//       187798876541