Simple Calculator using Module

'------------------------------------------------------------------------------------------
'           Notice of My Copyright and Intellectual Property Rights
'
' Any intellectual property contained within the program by Joseph L. Bolen remains the
' intellectual property of the Joseph L. Bolen. This means that no person may distribute,
' publish or provide such intellectual property to any other person or entity for any
' reason, commercial or otherwise, without the express written permission of Joseph L. Bolen.
'
'                 Copyright © 2014. All rights reserved.
'        All trademarks remain the property of their respective owners.
'-------------------------------------------------------------------------------------------
' Program Name:   Simple Calculator
' Author:         Joseph L. Bolen
' Date Created:   Sep 2014
'
' Description:    The program demonstrates the use of a module for shared functions.
'
' Documentation:
'                 Form's screen capture is at     -- http://imgur.com/m3H4SHx
'                 Original VB .Net code for Very Simple Calculator is at:
'                                                 -- http://pastebin.com/PcJ9nRdZ
'                 Visual Basic .Net codes is at   -- http://pastebin.com/ZhwtJxZy
'                 Video tutorial at YouTube       -- http://www.youtube.com/user/bolenpresents
'-------------------------------------------------------------------------------------------

Option Strict On

Public Class MainForm

#Region " Form Events"

    ' Allow form to close even if input errors exist.
    Private Sub MainForm_FormClosing(sender As Object, e As FormClosingEventArgs) _
        Handles Me.FormClosing

        e.Cancel = False
    End Sub

#End Region

#Region " Control Events"

    ' Add first number to second number and show the sum.
    Private Sub AddButton_Click(sender As Object, e As EventArgs) _
       Handles AddButton.Click

        ' Validate input.
        If Not ValidateChildren() Then
            My.Computer.Audio.PlaySystemSound(Media.SystemSounds.Hand)
            Exit Sub
        End If

        ' Process operation and output results to label.
        ResultValueLabel.Text = AddTwoNumbers(FirstNumberTextBox.Text, SecondNumberTextBox.Text).ToString("n3")

        ' Place cursor in first input textbox.
        FirstNumberTextBox.Focus()
        FirstNumberTextBox.SelectAll()
    End Sub

    ' Subtract the second number from first number and show the difference.
    Private Sub SubtractButton_Click(sender As Object, e As EventArgs) _
        Handles SubtractButton.Click

        ' Validate input.
        If Not ValidateChildren() Then
            My.Computer.Audio.PlaySystemSound(Media.SystemSounds.Hand)
            Exit Sub
        End If

        ' Process validated input and output results to label.
        ResultValueLabel.Text = SubtractTwoNumbers(FirstNumberTextBox.Text, SecondNumberTextBox.Text).ToString("n3")

        ' Place cursor in first input textbox.
        FirstNumberTextBox.Focus()
        FirstNumberTextBox.SelectAll()

    End Sub

    ' Multiply the first number by second number and show the product.
    Private Sub MultiplyButton_Click(sender As Object, e As EventArgs) _
        Handles MultiplyButton.Click

        ' Validate input.
        If Not ValidateChildren() Then
            My.Computer.Audio.PlaySystemSound(Media.SystemSounds.Hand)
            Exit Sub
        End If

        ' Process validated input and output results to label.
        ResultValueLabel.Text = MultiplyTwoNumbers(FirstNumberTextBox.Text, SecondNumberTextBox.Text).ToString("n3")

        ' Place cursor in first input textbox.
        FirstNumberTextBox.Focus()
        FirstNumberTextBox.SelectAll()

    End Sub

    ' Divide the first number by the second number and show the quotient.
    Private Sub DivideButton_Click(sender As Object, e As EventArgs) _
        Handles DivideButton.Click

        ' Validate input.
        If Not ValidateChildren() Then
            My.Computer.Audio.PlaySystemSound(Media.SystemSounds.Hand)
            Exit Sub
        End If

        ' Process validated input and output results to label.
        ResultValueLabel.Text = DivideTwoNumbers(FirstNumberTextBox.Text, SecondNumberTextBox.Text).ToString("n3")

        ' Place cursor in first input textbox.
        FirstNumberTextBox.Focus()
        FirstNumberTextBox.SelectAll()

    End Sub

    ' Clear the output controls and place cursor in first textbox.
    Private Sub ClearButton_Click(sender As Object, e As EventArgs) _
        Handles ClearButton.Click

        ' Clear output controls.
        ResultValueLabel.Text = String.Empty
        FirstNumberTextBox.Clear()
        SecondNumberTextBox.Clear()

        ' Clear ErrorProvider
        ErrorProvider1.Clear()

        ' Position cursor in first textbox.
        FirstNumberTextBox.Focus()
        FirstNumberTextBox.SelectAll()
    End Sub

    ' Clear ResultValueLabel when either first or second
    ' textbox value changes.
    Private Sub ClearResult(sender As Object, e As EventArgs) _
        Handles FirstNumberTextBox.TextChanged,
                SecondNumberTextBox.TextChanged

        ResultValueLabel.Text = String.Empty
    End Sub

    ' Validate FirstNumberTextBox input.
    Private Sub FirstNumberTextBox_Validating(sender As Object, e As System.ComponentModel.CancelEventArgs) _
        Handles FirstNumberTextBox.Validating

        If IsNumeric(FirstNumberTextBox.Text) Then
            ErrorProvider1.SetError(FirstNumberTextBox, String.Empty)
        Else
            ErrorProvider1.SetError(FirstNumberTextBox, "Numeric value required.")
            e.Cancel = True
        End If
    End Sub

    ' Validate SecondNumberTextBox input.
    Private Sub SecondNumberTextBox_Validating(sender As Object, e As System.ComponentModel.CancelEventArgs) _
        Handles SecondNumberTextBox.Validating


        If IsNumeric(SecondNumberTextBox.Text) Then
            ErrorProvider1.SetError(SecondNumberTextBox, String.Empty)
        Else
            ErrorProvider1.SetError(SecondNumberTextBox, "Numeric value required.")
            e.Cancel = True
        End If
    End Sub

#End Region

End Class

'=============================================================================================
' CalculatorMethods
'=============================================================================================
Module CalculatorMethods

    Public Function AddTwoNumbers(ByVal firstOperand As String, ByVal secondOperand As String) As Double
        Dim num1 As Double = Convert.ToDouble(firstOperand)
        Dim num2 As Double = Convert.ToDouble(secondOperand)
        Return (num1 + num2)
    End Function

    Public Function SubtractTwoNumbers(ByVal firstOperand As String, ByVal secondOperand As String) As Double
        Dim num1 As Double = Convert.ToDouble(firstOperand)
        Dim num2 As Double = Convert.ToDouble(secondOperand)
        Return (num1 - num2)
    End Function

    Public Function MultiplyTwoNumbers(ByVal firstOperand As String, ByVal secondOperand As String) As Double
        Dim num1 As Double = Convert.ToDouble(firstOperand)
        Dim num2 As Double = Convert.ToDouble(secondOperand)
        Return (num1 * num2)
    End Function

    Public Function DivideTwoNumbers(ByVal firstOperand As String, ByVal secondOperand As String) As Double
        Dim num1 As Double = Convert.ToDouble(firstOperand)
        Dim num2 As Double = Convert.ToDouble(secondOperand)
        Return (num1 / num2)
    End Function

End Module