Option Explicit
Private Sub Command1_Click()
Dim Wert As String, i As Long, Zähler As Long
   Wert = Text1.Text
   Zähler = 1
   For i = 1 To Len(Wert)
      If Mid(Wert, i, 1) = Chr(13) Then Zähler = Zähler + 1
   Next i
   MsgBox "Die Textbox hat " & Zähler & " Zeilen"
End Sub