Public Class Form1
    Inherits System.Windows.Forms.Form
    '形參a()為有序數(shù)組，low、high查找下界、上界，key查找關鍵值
    'index返回結果，查找到關鍵值在數(shù)組中的下標，找不到為-1
    Sub birsearch(ByRef a(), ByVal low, ByVal high, ByVal key, ByVal index)
        Dim mid, min As Integer
        mid = (low + high) \ 2        '取查找區(qū)間的中點
        If a(mid) = key Then
            index = mid               '查找到，返回查找到的下標
            Exit Sub
        ElseIf low > high Then        '二分法查找區(qū)間無元素，查找不到
            index = -1
            Exit Sub
        End If
        If key < a(mid) Then          '查找區(qū)間在上半部
            high = min - 1
        Else
            low = mid + 1             '查找區(qū)間在下半部
        End If
        Call birsearch(a, low, high, key, index)     '遞歸調用查找函數(shù)
        TextBox1.Text = index
    End Sub

#Region " Windows 窗體設計器生成的代碼 "

    Public Sub New()
        MyBase.New()

        '該調用是 Windows 窗體設計器所必需的。
        InitializeComponent()

        '在 InitializeComponent() 調用之后添加任何初始化

    End Sub

    '窗體重寫處置以清理組件列表。
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub

    'Windows 窗體設計器所必需的
    Private components As System.ComponentModel.IContainer

    '注意：以下過程是 Windows 窗體設計器所必需的
    '可以使用 Windows 窗體設計器修改此過程。
    '不要使用代碼編輯器修改它。
    Friend WithEvents Button1 As System.Windows.Forms.Button
    Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.Button1 = New System.Windows.Forms.Button
        Me.TextBox1 = New System.Windows.Forms.TextBox
        Me.SuspendLayout()
        '
        'Button1
        '
        Me.Button1.Location = New System.Drawing.Point(8, 8)
        Me.Button1.Name = "Button1"
        Me.Button1.TabIndex = 0
        Me.Button1.Text = "Button1"
        '
        'TextBox1
        '
        Me.TextBox1.Location = New System.Drawing.Point(96, 8)
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.Size = New System.Drawing.Size(184, 21)
        Me.TextBox1.TabIndex = 1
        Me.TextBox1.Text = ""
        '
        'Form1
        '
        Me.AutoScaleBaseSize = New System.Drawing.Size(6, 14)
        Me.ClientSize = New System.Drawing.Size(292, 273)
        Me.Controls.Add(Me.TextBox1)
        Me.Controls.Add(Me.Button1)
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)

    End Sub

#End Region
    Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim b() = {5, 13, 19, 21, 37, 56, 64, 75, 80, 88, 92}, n As Integer
        Call birsearch(b, LBound(b), UBound(b), 21, n%)
        TextBox1.Text = n
    End Sub
End Class