大一的VB程序设计！求大神告知！

Dim x1, x2, y As Single
Dim n As Integer
Private Sub Command1_Click(Index As Integer)
Text1.Text = Text1.Text + CStr(Index)
End Sub
Private Sub Command2_Click()
Text1.Text = Text1.Text + "."
End Sub
Private Sub Command3_Click(Index As Integer)
x1 = Val(Text1.Text)
Text1.Text = ""
n = Index
End Sub
Private Sub Command4_Click()
Text1.Text = Mid(Text1.Text, 1, Len(Text1.Text) - 1)
End Sub
Private Sub Command5_Click()
x1 = 0: x2 = 0: y = 0
Text1.Text = ""
End Sub
Private Sub Command6_Click()
Unload Me
End Sub
Private Sub Command7_Click()
x2 = Val(Text1.Text)
On Error GoTo errl
Select Case n
Case 0
y = x1 + x2
Case 1
y = x1 - x2
Case 2
y = x1 * x2
Case 3
y = x1 / x2
End Select
Text1.Text = CStr(y)
Exit Sub
errl:
MsgBox "您输入的数据有误,请重新输入", vbOKCancel + vbCritical, "错误!"
Text1.Text = ""
x1 = 0: x2 = 0: y = 0
Exit Sub
End Sub
Private Sub Command8_Click()
If Text1.Text <> "" Then
Text1.Text = -1 * Text1.Text
Else
End If
End Sub

0~9是一组控件，顺序可以调换