怎样VB 文本框从右向左移动?Text1.Left = Text1.Left + 100是向右移动,那向左呢?

Private Sub Form_Load()
Timer1.Interval = 100
Timer1.Enabled = True
End Sub
Private Sub Timer1_Timer()
Static a As Integer
If a = 0 Or Text1.Left a = 100
ElseIf Text1.Left > Me.ScaleWidth - Text1.Width Then
a = -100
End If
Text1.Left = Text1.Left + a
End Sub