vb.net小demo（计算器、文件处理等/C#也可看）

Demo1：使用窗体控件实现一个简易版计算器

Public Class Form1
    Private Sub Button_1_Click(sender As Object, e As EventArgs) Handles Button_1.Click
        CalSubBox.Text += Button_1.Text
    End Sub

    Private Sub Button_2_Click(sender As Object, e As EventArgs) Handles Button_2.Click
        CalSubBox.Text += Button_2.Text
    End Sub

    Private Sub Button_3_Click(sender As Object, e As EventArgs) Handles Button_3.Click
        CalSubBox.Text += Button_3.Text
    End Sub

    Private Sub Button_4_Click(sender As Object, e As EventArgs) Handles Button_4.Click
        CalSubBox.Text += Button_4.Text
    End Sub
    Private Sub Button_5_Click(sender As Object, e As EventArgs) Handles Button_5.Click
        CalSubBox.Text += Button_5.Text
    End Sub
    Private Sub Button_6_Click(sender As Object, e As EventArgs) Handles Button_6.Click
        CalSubBox.Text += Button_6.Text
    End Sub
    Private Sub Button_7_Click(sender As Object, e As EventArgs) Handles Button_7.Click
        CalSubBox.Text += Button_7.Text
    End Sub
    Private Sub Button_8_Click(sender As Object, e As EventArgs) Handles Button_8.Click
        CalSubBox.Text += Button_8.Text
    End Sub
    Private Sub Button_9_Click(sender As Object, e As EventArgs) Handles Button_9.Click
        CalSubBox.Text += Button_9.Text
    End Sub
    Private Sub Button_0_Click(sender As Object, e As EventArgs) Handles Button_0.Click
        CalSubBox.Text += Button_0.Text
    End Sub


    Private Sub Button_Add_Click(sender As Object, e As EventArgs) Handles Button_Add.Click
        CalSubBox.Text += Button_Add.Text

    End Sub

    Private Sub Button_Sub_Click(sender As Object, e As EventArgs) Handles Button_Sub.Click
        CalSubBox.Text += Button_Sub.Text
    End Sub

    Private Sub Button_Mul_Click(sender As Object, e As EventArgs) Handles Button_Mul.Click
        CalSubBox.Text += Button_Mul.Text
    End Sub

    Private Sub Button_Exc_Click(sender As Object, e As EventArgs) Handles Button_Exc.Click
        CalSubBox.Text += Button_Exc.Text
    End Sub
    Private Sub Button14_Click(sender As Object, e As EventArgs) Handles Button14.Click
        CalSubBox.Text += "."
    End Sub

    Private Sub Button_CE_Click(sender As Object, e As EventArgs) Handles Button_CE.Click
        ResultBox.Text = vbNullString
        CalSubBox.Text = ""
        N_S = ""
    End Sub

    Private Sub Button_C_Click(sender As Object, e As EventArgs) Handles Button_C.Click
        ResultBox.Text = vbNullString
        CalSubBox.Text = ""
        N_S = ""
    End Sub


    Public Result As Double
    Public ErrMsg As String = "正无穷大"
    Private Sub Button_Equal_Click(sender As Object, e As EventArgs) Handles Button_Equal.Click
        Try
            Dim result = New DataTable().Compute(CalSubBox.Text, Nothing) '将一个表达式进行运算
            ResultBox.Text = result '将结果显示出来

            If (ErrMsg = ResultBox.Text) Then
                ResultBox.Text = "除数不能为0"
            End If
        Catch ex As Exception
            MsgBox("无法计算:" & ex.Message)
        End Try

        Dim Split_Str As String() = CalSubBox.Text.Split({"+"c, "-"c, "/"c, "*"c}) 'Split_Str是分割后的单个字符串
        DelZero(Split_Str)
        Console.WriteLine("新字符串：" & N_S)
        CalSubBox.Text = DelLastChar(N_S) '去掉最后一个字符，展示到文本框中


    End Sub

    Function DelLastChar(s As String)
        Return s.Substring(0, s.Length - 1)
    End Function


    Function DelZero(ByVal StrArr As String())

        Dim Op_StrArr As String = GetOperateStr(CalSubBox.Text) '[+,-] 先获取整个字符串列表
        Dim Op_Str As String
        For i = 0 To StrArr.Length - 1  ' strArr实质上是分割后的单个字符串
            Console.WriteLine("第" & i + 1 & "次" & vbNewLine)
            Dim DelZero_S As String = StrArr(i).TrimStart({"0"c}) 'DelZero_S是抹零后的单个字符串、
            Console.WriteLine("抹零后：" & DelZero_S)
            If Not i = Op_StrArr.Length Then '最后一次不需要获取
                Op_Str = Op_StrArr(i) '获取当前的单个操作数，从字符串数组中获取
            End If

            Console.WriteLine("操作数：" + Op_Str)
            N_S += DelZero_S + Op_Str '将抹零的字符串 与 当前操作数拼接 '最后一次的单个操作数不变，用DelLastChar去掉即可


            Console.WriteLine("N_S：" & N_S)
            Console.WriteLine(" DelZero_S：" & DelZero_S)
        Next
        Return N_S
    End Function

    Function GetOperateStr(ByVal StrArr As String) '获取操作数，返回一个存放操作数的字符串数组
        Dim NewStrArr As String = ""
        For i = 0 To StrArr.Length - 1 '获取下标，从Index开始寻找第一个操作数，而不是重新开始
            If StrArr(i) = "+" Or StrArr(i) = "-" Or StrArr(i) = "*" Or StrArr(i) = "/" Then
                NewStrArr += StrArr(i)
            End If
        Next
        Return NewStrArr '字符串数组[+,-,]
    End Function


    Private Sub Button_Backspace_Click(sender As Object, e As EventArgs) Handles Button_Backspace.Click

        Try
            CalSubBox.Text = CalSubBox.Text.Substring(0, CalSubBox.Text.Length - 1) '回退一个字符:将字符串截取0，end-1赋值回去即可
        Catch ex As Exception
            MsgBox("发生错误:" & ex.Message)
            CalSubBox.Text = ""
        End Try

    End Sub


End Class

Demo2:对文件进行处理

要求：1.去掉当前文件的第一行

2.从第二行开始算，保留奇数行，去掉偶数行

3.将每一行的分隔符改为“/”

4.将每一行的2位和3位数字调换位置

5.将每一个数字保留2位小数

Imports System.IO


Module Module1
    Sub Main()
        Dim fr As New StreamReader("E:\T4-2.txt") '这里存放要处理的文件路径
        Dim fw As New StreamWriter("C:\Users\Public\Desktop\T4-2-处理.txt") '写到桌面的fw流的路径
        Dim data As String = ""
        Dim data1 As String = ""
        Dim new_data As String = ""
        fr.ReadLine() '跳过第一行中文字体，相当于第0行
        While data <> " " 'data读奇数行，data1读偶数行，遇到空格行就退出
            data = fr.ReadLine() '读取第一/三/五...行数据，并把读的内容赋值给当前data(data每次循环都会被重新赋值)
            If data = Nothing Then Exit While '当data读到空格行就退出循环，下同
            new_data = replace_splitChar(data) '将读取的data替换字符并返回给新data,此时的新data可以被写出
            Console.WriteLine("newData:" + new_data)
            fw.WriteLine(new_data， True) '写出 （重写）
            data1 = fr.ReadLine() '跳过第二/四/六...行,
            If data1 = Nothing Then Exit While '
        End While
        fr.Close()
        fw.Close()
        Console.WriteLine("已输出到桌面、按下任意键退出.....")
        Console.ReadKey()
    End Sub

    Function replace_splitChar(ByVal charStr As String)
        Dim new_str As String = "" '用一个新的Str来拼接/
        Dim new_str1 As String = ""

        Dim strArr As String() = charStr.Split(",") '分隔为字符串数组["110","23","12"]
        For Each s In strArr
            '把每个字符串保留两位小数
            Dim f_s = Double.Parse(s).ToString("0.00") 'f_s是保留两位小数的当前字符串
            new_str += f_s & "/" '拿到每一个字符串并拼接/ 赋值给新Str
        Next
        '交换的代码

        Dim strArr1 As String() = new_str.Split("/") '对newstr进行交换操作
        For i = 0 To new_str.Length - 1 'strArr就是字符串数组
            new_str1 = strArr1(0) + "/" + exchange(strArr(1), strArr(2)) + "/" + strArr1(3)
        Next


        Return new_str1
    End Function

    Function exchange(ByVal StrA As String, ByVal StrB As String) As String '将两个字符串进行交换位置的函数
        StrA = Double.Parse(StrA).ToString("0.00") '先转换再交换
        StrB = Double.Parse(StrB).ToString("0.00")
        Return StrB + "/" + StrA
    End Function


End Module

Demo3:OPenDialog和SaveDialog对话框案例(包括ToolStripMenu)

 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        OpenFileDialog1.InitialDirectory = "D:\"
        OpenFileDialog1.Filter = "纯文本文件(*.txt)|*.txt|所有文件(*.*)|*.*"
        OpenFileDialog1.Title = "打开文件"
        ' .RestoreDirectory = True '对话框关闭之前还原至当前目录
        If OpenFileDialog1.ShowDialog() = DialogResult.OK Then
            fileName = OpenFileDialog1.FileName 'OpenFileDialog1已经拿到文件名了
            fr = New StreamReader(fileName) '创建fileReader流通过文件名来读取文件
            RichTextBox1.Text = fr.ReadToEnd()  'fr已经获取到文件的所有信息，使用ReadToEnd()获取其内容
            fr.Close()
        End If
 End Sub
 
 Private Sub 打开文件ToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles 打开文件ToolStripMenuItem.Click
        OpenFileDialog1.InitialDirectory = "D:\"
        OpenFileDialog1.Filter = "纯文本文件(*.txt)|*.txt|所有文件(*.*)|*.*"
        OpenFileDialog1.Title = "打开文件"
        ' .RestoreDirectory = True '对话框关闭之前还原至当前目录
        If OpenFileDialog1.ShowDialog() = DialogResult.OK Then
            fileName = OpenFileDialog1.FileName 'OpenFileDialog1已经拿到文件名了
            fr = New StreamReader(fileName) '创建fileReader流通过文件名来读取文件
            RichTextBox1.Text = fr.ReadToEnd()  'fr已经获取到文件的所有信息，使用ReadToEnd()获取其内容
            fr.Close()
        End If

 End Sub