在线急等！给个计算器=号失效的理由

Private Sub Form_Load()
Dim sum1 As Double
Dim sum2 As Double
Dim operator As Integer
Dim pointflag As Boolean
Dim operatorNT As Boolean
pointflag = True    ‘小数点判断变量并赋值          
operatorNT = True   ‘运算符次数判断并赋值
End Sub
Private Sub Command1_Click(Index As Integer)
    Select Case Index
        Case 0      ‘ 数字键0
                If Val(Text1.Text) = 0 Then
                        Exit Sub
                Else
                            Text1.Text = Val(Text1.Text + Str(Index))
                End If
        Case 1 To 9   ‘数字键1到9
                            Text1.Text = Val(Text1.Text + Str(Index))
                            Text1.Text = Val(Text1.Text)
        Case 10        ‘小数点
                If ponitflag Then
                            Text1.Text = Text1.Text + "."
                            pointflag = False   ‘小数点出现一次
                End If
        Case 11         ‘   = 号
                            sum2 = Text1.Text
                Select Case operator
                    Case 1
                            Text1.Text = sum1 + sum2
                    Case 2
                            Text1.Text = sum1 - sum2
                    Case 3
                            Text1.Text = sum1 * sum2
                    Case 4
                            Text1.Text = sum1 / sum2
                End Select
                            pointflag = True     ‘使变量恢复初始
                            sum1 = Text1.Text
        Case 12 To 15     ‘算术运算符
                            sum1 = Text1.Text
                            Text1.Text = "0"
                            operator = Index - 11
                            pointflag = True    ‘使变量恢复初始
                            operatorNT = False
                If Not operatorNT Then
                            sum2 = Text1.Text
                End If
        Case 16             ‘未使用的控件
        Case 17             ‘清除键
                            Text1.Text = "0"
                            operatorNT = True    ‘初始化变量
    End Select
End Sub