form1.vb

Mastering VBNet Include Source Code

Public Class Form1
    Inherits System.Windows.Forms.Form

#Region " Windows Form Designer generated code "

    Public Sub New()
        MyBase.New()

        'This call is required by the Windows Form Designer.
        InitializeComponent()

        'Add any initialization after the InitializeComponent() call

    End Sub

    'Form overrides dispose to clean up the component list.
    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
    Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
    Friend WithEvents Button1 As System.Windows.Forms.Button
    Friend WithEvents Label1 As System.Windows.Forms.Label

    'Required by the Windows Form Designer
    Private components As System.ComponentModel.Container

    'NOTE: The following procedure is required by the Windows Form Designer
    'It can be modified using the Windows Form Designer.  
    'Do not modify it using the code editor.
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.TextBox1 = New System.Windows.Forms.TextBox()
        Me.Button1 = New System.Windows.Forms.Button()
        Me.Label1 = New System.Windows.Forms.Label()
        Me.SuspendLayout()
        '
        'TextBox1
        '
        Me.TextBox1.Font = New System.Drawing.Font("Trebuchet MS", 9.75!, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, CType(0, Byte))
        Me.TextBox1.Location = New System.Drawing.Point(80, 24)
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.Size = New System.Drawing.Size(120, 23)
        Me.TextBox1.TabIndex = 0
        Me.TextBox1.Text = ""
        '
        'Button1
        '
        Me.Button1.Font = New System.Drawing.Font("Trebuchet MS", 12!, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, CType(0, Byte))
        Me.Button1.Location = New System.Drawing.Point(80, 56)
        Me.Button1.Name = "Button1"
        Me.Button1.Size = New System.Drawing.Size(120, 56)
        Me.Button1.TabIndex = 1
        Me.Button1.Text = "Calculate Check Digit"
        '
        'Label1
        '
        Me.Label1.Font = New System.Drawing.Font("Trebuchet MS", 9.75!, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, CType(0, Byte))
        Me.Label1.Location = New System.Drawing.Point(40, 24)
        Me.Label1.Name = "Label1"
        Me.Label1.Size = New System.Drawing.Size(40, 23)
        Me.Label1.TabIndex = 2
        Me.Label1.Text = "ISBN"
        '
        'Form1
        '
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(208, 117)
        Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.Label1, Me.Button1, Me.TextBox1})
        Me.Name = "Form1"
        Me.Text = "ISBN Demo"
        Me.ResumeLayout(False)

    End Sub

#End Region

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        If Not IsNumeric(TextBox1.Text) Then
            MsgBox("ISBN may not contains characters!")
            Exit Sub
        Else
            If TextBox1.Text.Length <> 9 Then
                MsgBox("Please enter the first 9 digits of the ISBN!")
                Exit Sub
            Else
                MsgBox("The check digit is " & ISBNCheckDigit(TextBox1.Text))
            End If
        End If
    End Sub

    Function ISBNCheckDigit(ByVal ISBN As String) As String
        Dim i As Integer, chksum, chkDigit As Integer
        For i = 0 To 8
            chkSum = chkSum + (10 - i) * ISBN.Substring(i, 1)
        Next
        chkDigit = 11 - (chkSum Mod 11)
        If chkDigit = 10 Then
            Return ("X")
        Else
            Return (chkDigit.ToString)
        End If
    End Function

End Class