1. Dim v As Boolean '是否第一次按运算符
   Dim x, y As Double '存放两次数
   Private Sub Cmdcompute_Click(Index As Integer)
   If v Then '第一次运算符
   x = Val(Txtoutput.Text) '保存
   v = False
   Else
   y = Val(Txtoutput.Text)
   Select Case Index
   Case 0
   Txtoutput.Text = x + y
2. Case 1
   Txtoutput.Text = x - y
3. Case 2
   Txtoutput.Text = x * y
4. Case 3
   If y <> 0 Then
   Txtoutput.Text = x / y
   Else
   MsgBox ("Error") '如果除数为0，报错
   Txtoutput.Text = x
   v = False
   End If
   Case4
   y = 0
   v = False
   End Select
   x = Val(Txtoutput.Text)
   End If

End Sub

Private Sub CmdNegative_Click()
Txtoutput.Text = Trim(Str(-Val(Txtoutput.Text)))
End Sub

Private Sub CmdNumber_Click(Index As Integer)
If Index = 10 Then
Txtoutput.Text = "0."
Else
Txtoutput.Text = CmdNumber(Index).Caption

End If

End Sub

Private Sub Command1_Click()

End Sub

Private Sub Command2_Click()
Txtoutput.Text = ""
v = False

End Sub

Private Sub end_Click()
Unload Me
End Sub

为什么 我在点 Cmdcompute时，出错，麻烦说详细一点，谢谢。

Private Sub Cmdcompute_Click(Index As Integer)
If v Then '第一次运算符
x = Val(Txtoutput.Text) '保存
v = False
Else
y = Val(Txtoutput.Text)
Select Case Index
Case 0
Txtoutput.Text = x + y
Case 1
Txtoutput.Text = x - y
Case 2
Txtoutput.Text = x * y
Case 3
If y <> 0 Then
Txtoutput.Text = x / y
Else
MsgBox ("Error") '如果除数为0，报错
Txtoutput.Text = x
v = False
End If
Case4
y = 0
v = False
End Select
x = Val(Txtoutput.Text)
End If
End Sub

在这里出现问题？

是呀