Public Function ConvertNumber(ByVal number As String, ByVal base_alphabet_from _
  As String, _
        ByVal base_alphabet_to As String) As String
 
 
        Dim base_from As Integer = Len(base_alphabet_from)
        Dim base_to As Integer = Len(base_alphabet_to)
        Dim null_from As String = base_alphabet_from.Substring(0, 1)
        Dim new_number As String = ""
        Dim result_division As String
        Dim result_modulo As Integer
        Dim result_div As Integer
        Dim index As Integer
 
        Try
            Do
                index = 0
                result_modulo = base_alphabet_from.IndexOf(number.Substring(0, _
                  1))
                result_division = ""
 
                Do
                    If (result_modulo >= base_to) Then
                        result_div = result_modulo / base_to
                        result_division = result_division + (SubRight( _
                          base_alphabet_from, result_div, result_div + _
                          1)).ToString
                        result_modulo = result_modulo - (result_div * base_to)
                    Else
                        result_division = result_division + null_from
                    End If
                    index = index + 1
 
                    If index >= Len(number) Then
                        Exit Do
                    End If
                    result_modulo = (result_modulo * base_from) + _
                      base_alphabet_from.IndexOf(SubRight(number, index, index _
                      + 1))
 
                Loop
 
                index = 0
 
                Do
                    If index >= Len(result_division) Then
                        Exit Do
                    End If
                    If SubRight(result_division, index, index + 1).ToString _
                      <> null_from Then
                        Exit Do
                    End If
 
                    index = index + 1
                Loop
 
                result_division = SubRight(result_division, index, Len( _
                  result_division))
                new_number = (SubRight(base_alphabet_to, result_modulo, _
                result_modulo + 1)).ToString + new_number
                number = result_division
 
            Loop Until number = ""
        Catch e As Exception
            MsgBox(e.ToString)
        End Try
 
        Return new_number
    End Function
 
Public Function SubRight(ByVal text As String, ByVal start As String, ByVal _
  lange As String) As Integer
 
        Try
            Return text.Substring(start, lange)
        Catch ex As Exception
            Return SubRight(text, start, lange - 1)
        End Try
 
End Function
 
'Aufruf:
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        txtnew.Text = ConvertNumber(txtnumber.Text, txtfrom.Text, txtto.Text)
End Sub