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通过之前的学习，大家对窗体和控件知识已经有了初步的理解，本节开始将进行一些综合编程训练。

先从简单开始，综合编程1 计算器。

先考虑一下计算器的设计，可以参考windows的计算器。最基本那种就可以了。

下面是一个计算器控件摆放和命名：

txtValue的readonly属性设置为true；按钮的FlatStyle属性设置为Popup。

代码比较容易懂，我直接给出来：

1.  
   '做运算的第一个数字
2.  
   Dim numFirst As Double
3.  
   '做运算的第二个数字
4.  
   Dim numSecond As Double
5.  
   '运算符号
6.  
   Dim operatesymbol As String
7.  
    
8.  
   '清除
9.  
   Private Sub btnClear_Click(sender As Object, e As EventArgs) Handles btnClear.Click
10.  
    txtValue.Text = "0"
11.  
    operatesymbol = ""
12.  
    End Sub
13.  
     
14.  
    '删除最后一个数字
15.  
    Private Sub btnBack_Click(sender As Object, e As EventArgs) Handles btnBack.Click
16.  
    If txtValue.Text.Length = 1 Then
17.  
    txtValue.Text = "0"
18.  
    ElseIf txtValue.Text.Length > 1 Then
19.  
    txtValue.Text = txtValue.Text.Substring(0, txtValue.Text.Length - 1)
20.  
    End If
21.  
    End Sub
22.  
     
23.  
    '按下数字按钮
24.  
    Private Sub btn1_Click(sender As Object, e As EventArgs) Handles _
25.  
    btn1.Click, btn2.Click, btn3.Click,
26.  
    btn4.Click, btn5.Click, btn6.Click,
27.  
    btn7.Click, btn8.Click, btn9.Click
28.  
    Dim btnclick As Button = CType(sender, Button)
29.  
    Dim addnumber As String = btnclick.Text
30.  
    Select Case txtValue.Text
31.  
    Case "0"
32.  
    txtValue.Text = addnumber
33.  
    Case "-0"
34.  
    txtValue.Text = "-" & addnumber
35.  
    Case Else
36.  
    txtValue.Text &= addnumber
37.  
    End Select
38.  
    End Sub
39.  
     
40.  
    '按下小数点
41.  
    Private Sub btnDot_Click(sender As Object, e As EventArgs) Handles btnDot.Click
42.  
    txtValue.Text &= "."
43.  
    End Sub
44.  
     
45.  
    '按下正负号按钮
46.  
    Private Sub btnNegPos_Click(sender As Object, e As EventArgs) Handles btnNegPos.Click
47.  
    If txtValue.Text.Substring(0, 1) = "-" Then
48.  
    txtValue.Text = txtValue.Text.Substring(1, txtValue.Text.Length - 1)
49.  
    Else
50.  
    txtValue.Text = "-" & txtValue.Text
51.  
    End If
52.  
    End Sub
53.  
     
54.  
    '按下运算符按钮
55.  
    Private Sub btnOperate_Click(sender As Object, e As EventArgs) Handles btnAdd.Click, btnSub.Click, btnDiv.Click, btnMul.Click
56.  
    Dim btnclick As Button = CType(sender, Button)
57.  
    numFirst = Double.Parse(txtValue.Text)
58.  
    operatesymbol = btnclick.Text
59.  
    txtValue.Text = "0"
60.  
    End Sub
61.  
     
62.  
    '按下等于按钮
63.  
    Private Sub btnEqual_Click(sender As Object, e As EventArgs) Handles btnEqual.Click
64.  
    numSecond = Double.Parse(txtValue.Text)
65.  
    Dim dbValue As Double
66.  
     
67.  
    Select Case operatesymbol
68.  
    Case "+"
69.  
    dbValue = numFirst + numSecond
70.  
    Case "-"
71.  
    dbValue = numFirst - numSecond
72.  
    Case "*"
73.  
    dbValue = numFirst * numSecond
74.  
    Case "/"
75.  
    dbValue = numFirst / numSecond
76.  
    Case ""
77.  
    Exit Sub
78.  
    Case Else
79.  
    Exit Sub
80.  
    End Select
81.  
    Dim strValue As String = dbValue.ToString
82.  
     
83.  
    txtValue.Text = strValue
84.  
    End Sub
85.  
     
86.  
    '按下平方按钮
87.  
    Private Sub btnSquare_Click(sender As Object, e As EventArgs) Handles btnSquare.Click
88.  
    Dim btnclick As Button = CType(sender, Button)
89.  
    numFirst = Double.Parse(txtValue.Text)
90.  
     
91.  
    Dim dbValue As Double
92.  
    dbValue = numFirst ^ 2
93.  
    Dim strValue As String = dbValue.ToString
94.  
     
95.  
    txtValue.Text = strValue
96.  
    End Sub

也显而易见代码中还存在些bug，请试着改正：

1、运行完毕后，数字按钮按下将会添加到运算结果后面；

2、数字除以0或者结果超大的时候会显示“正无穷大”，任然可以参与运算，但是会导致错误；

3、多次按下运算符会导致误认为第一个做计算的数字为0，导致结果不正确。