Private Sub but_click(ByVal sender As Object, ByVal e As EventArgs)
    Dim i As Integer = -1
    For Each key As String In mytextBoxes.Keys
       i += 1
       If IsNumeric(mytextBoxes(key).Text) Then
          inhalt(i) = CStr(mytextBoxes(key).Text)
       End If
       mytextBoxes(key).Text = String.Empty
    Next key
End Sub