字符函数验证：

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles Button1.Click
        TextBox2.Text = Len(TextBox1.Text)
        Label2.Text = Button1.Text & "函数的结果"
    End Sub

    Private Sub Button4_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles Button4.Click
        TextBox2.Text = Trim(TextBox1.Text)
        Label2.Text = Button4.Text & "函数的结果"
    End Sub

    Private Sub Button5_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles Button5.Click
        Dim a%
        a = InputBox("请输入重复出现的次数（必须为数字）","StrDup函数")
        TextBox2.Text = StrDup(a,TextBox1.Text)
        Label2.Text = Button5.Text & "函数的结果"
    End Sub

    Private Sub Button6_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles Button6.Click
        Dim b$
        b = InputBox("输入查找字串","InStr函数")
        TextBox2.Text = InStr(TextBox1.Text,b)
        Label2.Text = Button6.Text & "函数的结果"
    End Sub

    Private Sub Button7_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles Button7.Click
        Dim c$,d$
        c = InputBox("输入需要替换的字符串","Replace函数")
        d = InputBox("输入替换后的字符串","Replace函数")
        TextBox2.Text = Replace(TextBox1.Text,c,d)
        Label2.Text = Button7.Text & "函数的结果"
    End Sub

    Private Sub Button8_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles Button8.Click
        Dim m%,n%
        m = InputBox("输入从左开始取得位置(必须为数字）","Mid函数")
        n = InputBox("输入要取得字符数（必须为数字）","Mid函数")
        TextBox2.Text = Mid(TextBox1.Text,m,n)
        Label2.Text = Button8.Text & "函数的结果"
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles MyBase.Load

    End Sub
End Class