Public Class Form1
    Inherits System.Windows.Forms.Form
    Public Function trapez(ByVal a As Double, ByVal b As Double, ByVal n As Integer) As Single
        Dim sum, h, x As Double : Dim i
        h = (b - a) / n
        sum = (f(a) + f(b)) / 2
        For i = 1 To n - 1
            x = a + i * h
            sum = sum + f(x)
        Next I
        trapez = sum * h
    End Function
    Public Function f(ByVal x As Double)
        f = x * x * x + 2 * x + 5           '對不同的被積函數在此作對應的改動
    End Function

#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 TextBox1 As System.Windows.Forms.TextBox
    Friend WithEvents Label1 As System.Windows.Forms.Label
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.TextBox1 = New System.Windows.Forms.TextBox
        Me.Label1 = New System.Windows.Forms.Label
        Me.SuspendLayout()
        '
        'TextBox1
        '
        Me.TextBox1.Location = New System.Drawing.Point(88, 40)
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.TabIndex = 0
        Me.TextBox1.Text = ""
        '
        'Label1
        '
        Me.Label1.Location = New System.Drawing.Point(32, 8)
        Me.Label1.Name = "Label1"
        Me.Label1.Size = New System.Drawing.Size(120, 23)
        Me.Label1.TabIndex = 1
        Me.Label1.Text = "數值積分的結果為"
        '
        'Form1
        '
        Me.AutoScaleBaseSize = New System.Drawing.Size(6, 14)
        Me.ClientSize = New System.Drawing.Size(292, 273)
        Me.Controls.Add(Me.Label1)
        Me.Controls.Add(Me.TextBox1)
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)

    End Sub

#End Region
    Private Sub Form1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Click
        TextBox1.Text = trapez(1, 3, 30)
    End Sub
End Class