Public Class frmStepper
 
    Dim WithEvents btnUp10 As New Button With _
        {.Parent = Me, .Top = 100, .Text = "+10"}
    Dim WithEvents btnDown10 As New Button With _
        {.Parent = Me, .Top = 130, .Text = "-10"}
    Dim WithEvents btnUp5 As New Button With _
        {.Parent = Me, .Top = 160, .Text = "+5"}
    Dim WithEvents btnDown5 As New Button With _
        {.Parent = Me, .Top = 190, .Text = "-5"}
 
    Dim WithEvents lblIndex As New Label With _
        {.Parent = Me, .Top = 220, .Width = 200}
 
    ''' <summary>Umlaufende Indizierung</summary>
    ''' <param name="stp">Schrittweite</param>
    ''' <param name="ug">Untergrenze</param>
    ''' <param name="og">Obergrenze</param>
    ''' <param name="Init">Initialisierung: Index = Untergrenze</param>
    ''' <returns>Aktueller Index</returns>
    Private Function StepAround(ByVal stp As Integer, _
        ByVal ug As Integer, ByVal og As Integer, _
        Optional ByVal Init As Boolean = False) As Integer
 
        Static current As Integer = ug
 
        If stp = 0 OrElse Math.Abs(stp) > og - ug OrElse og <= ug Then
            Throw New ArgumentException("Ungültige Step-Parameter")
        End If
 
        If Init Then
            current = ug
        Else
            current += stp
            If current > og Then current -= og : current += ug 'alternativ: ( 
            ' ug - 1)
            If current < ug Then current = og - (ug - current)
        End If
        Return current
    End Function
 
 
    Private Sub btn_Click(sender As Object, e As System.EventArgs) _
        Handles btnDown10.Click, btnDown5.Click, btnUp10.Click, btnUp5.Click
 
        Dim btn As Button = DirectCast(sender, Button)
        Dim stp As Integer = CInt(btn.Text)
        lblIndex.Text = "Index = " & StepAround(stp, 0, 350).ToString
 
    End Sub
 
End Class