Private Sub Command1_Click(Index As Integer)
 Select Case Index
   Case 0
     Text1.Text = Text1.Text & "1"
   Case 1
     Text1.Text = Text1.Text & "2"
   Case 2
     Text1.Text = Text1.Text & "3"
   Case 3
    Text1.Text = Text1.Text & "4"
   Case 4
     If sum <> "" Then
     Text1.Text = Val(sum) + Val(Text1.Text)
    Else
     sum = Text1.Text
     Text1.Text = ""
    End If
   End Select
End Sub
想实现连加始终要多单击一次加号键，请问一下如何改正（case 4代表+键）