Hat man eine Nummer und möchte dynamisch eine Folgenummer bilden, die sich nach dem letzten Zeichen richtet, kann man in Visual Basic folgende Funktion verwenden:

Imports System.Text.RegularExpressions

Module VBModule

    Function NextLetter(c As String) As String

        If c = "Z" Then

            Return "Z-1"

        ElseIf c = "z" Then

            Return "z-1"

        End If

        Return Chr(Asc(c) + 1)

    End Function

    Function NextNr(ByVal val As String) As String

        Dim regPatternNumber As String = "\d+$"
        Dim regNumber As Regex = New Regex(regPatternNumber)
        Dim matchNumber As Match = regNumber.Match(val)

        Dim regPatternChar As String = "[A-Za-z]+$"
        Dim regChar As Regex = new Regex(regPatternChar)
        Dim matchChar As Match = regChar.Match(val)

        If matchNumber.Success Then

            Dim NextNumber As Integer = Convert.toInt32(matchNumber.value)
            NextNumber = NextNumber + 1

            Return Regex.Replace(val, regPatternNumber, cstr(NextNumber))

        ElseIf matchChar.Success Then

            Return Regex.Replace(val, regPatternChar, NextLetter(matchChar.value))

        Else

            Return val + "-1"

        End If

        Return "_"

    End Function

    Sub Main()

        Console.WriteLine(NextNr("A/1"))
        Console.WriteLine(NextNr("A/1/B"))
        Console.WriteLine(NextNr("A/1/Z"))
        Console.WriteLine(NextNr("A/1/["))
        Console.WriteLine(NextNr("A/1/10"))

    End Sub

End Module

Die gleiche Funktion in PHP findet man hier.