Button-Based Controls

 Introduction to Command Buttons

 Description
 On a typical application, a button is an object that the user clicks to perform an action. To make this obvious, a button is a control surrounded by thick borders. Here is an example of a button on a form: Although a control is usually positioned on a form, there various other control containers that can hold a button. These include the toolbar or the status bar, and the other containers we have used so far.

To indicate what it is used for, a button displays some text as its caption. A button can also display a picture instead. Another button can display both a string and a picture. When you create a button, you will decide what it should display and how it should behave.

 Practical Learning: Introducing Buttons
1. Start Microsoft Visual Basic and create a Windows Application named Algebra1
2. In the Solution Explorer, right-click Form1.vb and click Rename
3. Type Exercise.vb and press Enter
4. Click the body of the form to make sure it is selected.
In the Properties window, change the following characteristics
FormBorderStyle: FixedDialog
Text: Factorial, Permutation, and Combination
Size: 304, 235
StartPosition: CenterScreen
MaximizeBox: False
MinimizeBox: False
5. In the Containers section of the Toolbox, click TabControl and click the form
6. On the form, right-click the right side of tabPage2 and click Add Page
7. Based on what we learned in Lesson 19, design the form as follows:

 Control Text Name Additional Properties TabControl tclAlgebra HotTrack: True Location: 12, 12 Size: 304, 235 TabPage Factorial tabFactorial Label Number: Location: 22, 21 TextBox txtNumber TextAlign: Right Location: 88, 18 Size: 50, 20 Label Result: Location: 22, 56 TextBox txtFactorial TextAlign: Right Location: 88, 54 Size: 140, 20
 Control Text Name Location Size TabPage Permutation tabPermutation Label n: 22, 21 TextBox txtPermutationN 88, 18 50, 20 Label r: 22, 56 TextBox txtPermutationR 88, 54 50, 20 Label P(n, r): 22, 92 TextBox txtPermutation 88, 90 140, 20
 Control Text Name Location Size TabPage Combination tabCombination Label n: 22, 21 TextBox txtCombinationN 88, 18 50, 20 Label r: 22, 56 TextBox txtCombinationR 88, 54 50, 20 Label C(n, r): 22, 92 TextBox txtCombination 88, 90 140, 20
8. Right-click the form and click View Code
9. Create the following functions:

 ```Public Class Exercise Private Function Factorial(ByVal x As Long) As Long If x <= 1 Then Return 1 Else Factorial = x * Factorial(x - 1) End If End Function Private Function Permutation(ByVal n As Long, ByVal r As Long) As Long If r = 0 Then Permutation = 0 If n = 0 Then Permutation = 0 If (r >= 0) And (r <= n) Then Permutation = Factorial(n) / Factorial(n - r) Else Permutation = 0 End If End Function Private Function Combinatorial(ByVal a As Long, ByVal b As Long) As Long If a <= 1 Then Combinatorial = 1 Combinatorial = Factorial(a) / (Factorial(b) * Factorial(a - b)) End Function End Class```
10. Click the Exercise.vb [Design] tab
 Creating a Button

To support the buttons of an application, the .NET Framework provides an abstract class named ButtonBase. The regular button of Microsoft Windows is implemented by the Button class. At design time, to add a button to your project, from the Common Controls section of the Toolbox, you can click the Button and click the form or another container.

To programmatically create a button, you can declare a variable of type Button and use the new operator to allocate memory for it. Here is an example:

```Imports System.Drawing
Imports System.Windows.Forms

Module Exercise

Public Class Starter
Inherits Form

Private btnResume As Button

Dim components As System.ComponentModel.Container

Public Sub New()
InitializeComponent()
End Sub

Public Sub InitializeComponent()

btnResume = New Button()

End Sub

End Class

Function Main() As Integer

Dim frmStart As Starter = New Starter

Application.Run(frmStart)

Return 0
End Function

End Module```
 Practical Learning: Creating Buttons
1. In the combo box on top of the Properties window, select tabFactorial
2. From the Common Controls section of the Toolbox, click Button and click on the right side of the top text box
 The Characteristics of a Button

 The Caption of a Button

For a user, the most important aspects of a button are the message it displays and the action it performs. The text the button displays allows the user to know what the button is used for. This is represented by the Text property. The most popular strings that the buttons display are OK and Cancel. The OK caption is set for a form or a dialog box that informs the user of an error, an intermediary situation, or an acknowledgement of an action that was performed on the dialog that hosts the button. The Cancel caption is useful on a button whose main parent (the form or the dialog box) would ask a question or request a follow-up action from the user. Whenever a dialog box allows the user to dismiss it without continuing the action, you should provide a button with a Cancel caption.

After adding a button to a form (by design or with code), you can change its caption with code by assigning the desired string to the Text property. For example, you can change the caption of a button as follows:

`button1.Text = "Let it Go!";`

After specifying the Text of a button, by default, it's positioned in the middle center of the button:

The position of the text of a button is controlled through the TextAlign property which is a value of the ContentAlignment enumerator. The possible values are:

 TopLeft TopCenter TopRight MiddleLeft MiddleCenter MiddleRight BottomLeft BottomCenter BottomRight

Here is an example:

```Public Sub InitializeComponent()

btnResume = New Button()
btnResume.Text = "Resume"
btnResume.Location = New Point(32, 20)
btnResume.Size = New System.Drawing.Size(120, 48)

btnResume.TextAlign = ContentAlignment.BottomCenter

End Sub```

 Practical Learning: Using the Buttons
1. Access each tab page and add a button to it
2. Add a button to the form under the tab control
3. Complete the design of the form as follows:

 Control Text Name Button Calculate btnCalcFactorial Button Close btnClose
 Control Text Name Button Calculate btnCalcPermutation
 Control Text Name Button Calculate btnCalcCombination
4. Right-click the form and click View Code
5. In the Class Name combo box, select btnCalcFactorial
6. In the Method Name combo box, select Click and implement the event as follows:

 ```Private Sub btnCalcFactorial_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnCalcFactorial.Click Dim number As Long Dim Result As Long Try number = CLng(txtFactNumber.Text) Result = Factorial(number) txtFactorial.Text = Result.ToString() Catch ex As Exception MsgBox("Invalid Number") End Try End Sub```
7. In the Class Name combo box, select btnCalcPermutation
8. In the Method Name combo box, select Click and implement the event as follows:

 ```Private Sub btnCalcPermutation_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnCalcPermutation.Click Dim n As Long Dim r As Long Dim Result As Long Try n = CLng(txtPermutationN.Text) Catch ex As Exception MsgBox("Invalid Number") End Try Try r = CLng(txtPermutationR.Text) Result = Permutation(n, r) txtPermutation.Text = Result.ToString() Catch ex As Exception MsgBox("Invalid Number") End Try End Sub```
9. In the Class Name combo box, select btnCalcCombination
10. In the Method Name combo box, select Click and implement the event as follows:

 ```Private Sub btnCalcCombination_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnCalcCombination.Click Dim n As Long Dim r As Long Dim Result As Long Try n = CLng(txtCombinationN.Text) Catch ex As Exception MsgBox("Invalid Number") End Try Try r = CLng(txtCombinationR.Text) Result = Combinatorial(n, r) txtCombination.Text = Result.ToString() Catch ex As Exception MsgBox("Invalid Number") End Try End Sub```
11. In the Class Name combo box, select btnClose
12. In the Method Name combo box, select Click and implement the event as follows:

 ```Private Sub btnClose_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnClose.Click End End Sub```
13. Execute the application to test the calculations

 The Image on a Button

Besides, or instead, of a caption, a button can display a picture on top. If you want a button to display a bitmap, you should first create, design, or have a picture. Then, in the Properties window, use the Image field to select a bitmap or an icon. You can also programmatically assign an Image object to the Image property. Here is an example:

```Public Sub InitializeComponent()

btnResume = New Button()
btnResume.Text = "Resume"
btnResume.Location = New Point(32, 20)
btnResume.Size = New System.Drawing.Size(120, 48)

btnResume.Image = Image.FromFile("E:\Programs\neutral.gif")

End Sub```

This would produce:

By default, both the caption and the image display ion the middle-center of the button. To make them distinct and allow the user to see both, you can design a bitmap that has both and assign that bitmap as the image of the button. Alternatively, you can use a separate string and a separate picture. Fortunately, each can have its own alignment. We already saw how to control the alignment of the caption.

Besides displaying an image, the Button class is equipped with the ImageAlign property that allows you to specify the alignment of the image. The ImageAlign property is inherited from the ButtonBase class. The ButtonBase.ImageAlign property is based on the ContentAlignment enumeration that we are already familiar with. Here is an example:

```Public Sub InitializeComponent()

btnResume = New Button()
btnResume.Text = "Resume"
btnResume.Location = New Point(32, 20)
btnResume.Size = New System.Drawing.Size(120, 48)

btnResume.TextAlign = ContentAlignment.BottomCenter
btnResume.Image = Image.FromFile("E:\Programs\neutral.gif")
btnResume.ImageAlign = ContentAlignment.TopCenter

End Sub```

This would produce:

Instead of using the Image property, you can first create an image list and add some pictures to it. Then, using the ImageList property, assign it to the button. Use the ImageIndex property to specify what picture would be displayed on the button.

 Practical Learning: Using a Picture on a Button
1. To start a new application, on the main menu, click File -> New -> Project
2. In the Templates list, click Windows Application and change the Name to SimpleInterest1
3. Click OK
5. In the Templates list, click Icon File
6. Change the Name to Calculator and click OK
7. Right-click a white area in the icon designer -> Delete Image Type
8. Right-click the icon designer again -> Current Icon Image Types -> 16x16, 16 colors
9. Design the icon as follows:

11. In the Templates list, click Icon File and change the Name to exit
13. Right-click a white area in the icon designer -> Delete Image Type
14. Right-click the icon designer again -> Current Icon Image Types -> 16x16, 16 colors
15. Design the icon as follows:

16. Save and close the icon window
17. In the Solution Explorer, right-click Form1.vb and click Rename
18. Type SimpleInterest.vb and press Enter twice
19. Design the form as follows:

 Control Text Name TextAlign GroupBox Loan Preparation Label Principal TextBox 0.00 txtPrincipal Right Label Interest Rate: TextBox 0.00 txtInterestRate Right Label % Label Periods: TextBox 1 txtPeriods Right Label Months Button Calculate btnCalculate Button Close btnClose GroupBox Results Label Interest Earned: TextBox 0.00 txtInterestEarned Right Label Future Value TextBox 0.00 txtFutureValue Right
20. On the form, click the Calculate button
21. In the Properties window, click Image and click its ellipsis button
22. In the Select Resource dialog box, click Import
23. In the Files of Type box, select All Files
24. Locate the folder of the current project, select Calculator.ico and click Open
25. On the Select Resource dialog box, click OK
26. Change the following properties of the Calculate button:
ImageAlign: TopCenter
TextAlign: BottomCenter
27. On the form, click the Calculate button
28. In the Properties window, click Image and click its ellipsis button
29. In the Select Resource dialog box, click Import
30. In the Files of Type box, select All Files
31. Locate the folder of the current project, select exit.ico and click Open
32. On the Select Resource dialog box, click OK
33. Change the following properties of the Close button:
ImageAlign: TopCenter
TextAlign: BottomCenter

34. On the form, double-click the Calculate button and implement its Click event as follows:

 ```Private Sub btnCalculate_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) _ Handles btnCalculate.Click Dim Principal As Double Dim InterestRate As Double Dim InterestEarned As Double Dim FutureValue As Double Dim Periods As Double Dim I As Double Dim p As Double Try Principal = CDbl(txtPrincipal.Text) Catch ex As Exception MsgBox("The value you entered for the " & _ "principal is not valid") End Try Try InterestRate = CDbl(txtInterestRate.Text) Catch ex As Exception MsgBox("Wrong Value: The interest rate must " & _ "be a value between 0 and 100") End Try Try Periods = CDbl(txtPeriods.Text) Catch ex As Exception MsgBox("You entered an invalid value for the periods") End Try i = InterestRate / 100 p = Periods / 12 InterestEarned = Principal * i * p FutureValue = Principal + InterestEarned txtInterestEarned.Text = InterestEarned.ToString("C") txtFutureValue.Text = FutureValue.ToString("C") End Sub```
35. In the Class Name combo box, select btnClose
36. In the Method Name combo box, select Click and implement the event as follows:

 ```Private Sub btnClose_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnClose.Click End End Sub```
37. Execute the application and test the calculation

 The Flat Style of a Button

A regular button displays with raised borders as originally set by the operating system. To give your button a fancy look and behavior, you can use the FlatStyle property. The FlatStyle property is based on an enumeration of the same name. It provides 4 values that are:

• Flat: The button appears flat. When the mouse is over it, it becomes highlighted

• Popup: The button appears flat. When the mouse is over it, the borders of the button are raised

• Standard: The button appears and behave like all regular buttons you have seen

• System: The appearance of the button depends on the operating system

Obviously the most important and the most intuitive event of a button occurs when clicked. This event is of type EventArgs, which indicates that it doesn't provide nor does it need any formal details about what is going on. To launch this event, you can double-click the button on the form. To create this event programmatically, first implement the method that would carry its assignment, then increment-add (with the += operator) it to the Click property of the button by assigning it the EventHandler constructor.

 The Result of a Dialog Box

After the user has used a form or dialog box, to close it, the user would click a button. When the user does this, you must find out what button was clicked. Although there are various ways you can get this information, to assist you, the .NET Framework provides a convenient mechanism through an enumeration named DialogResult.

When creating a form or a dialog box, after adding a button, in the Properties window, click DialogResult and select on the values:

Except for None, by default, it does not matter what value you select but, you should follow Windows standard to select the right value.

After specifying the returned value of a button, access the properties of the form or dialog box:

• If you had selected OK as the DialogResult value of a button, you should select the name of that button for the AcceptButton property of the form
• If you had selected Cancel as the DialogResult value of a button, you should select the name of that button for the CancelButton property of the form

After configuring the DialogResult of the button(s), when the user clicks one of the buttons to close the form or dialog box, you can get the value of the Form.ShowDialog() method which returns one of the values of the DialogResult enumeration.

 Description

A radio button, sometimes called an option button, is a circular control that comes in a group with other radio buttons. Each radio button is made of a small empty circle O. From the group, when the user clicks one of them, the radio button that was clicked becomes filled with a big dot 8. When one of the radio buttons in the group is selected and displays its dot, the others display empty circles. To guide the user as to what the radio buttons mean, each is accompanied by a label.

Here is an example of a form with three radio buttons: Small, Medium, and Large

To create a radio button, on the Toolbox, you can click the RadioButton control . To programmatically create a radio button, declare a variable of type RadioButton, use the new operator to allocation memory for it and add it to the Controls collection of its parent. Because radio buttons always come as a group, you should include them in another control that visibly shows that the radio buttons belong together. The most common control used for this purpose is the group box created using the GroupBox control.

 The Location of a Radio Button

Unlike most of other controls that can be positioned anywhere, a radio button should not be placed directly on a form. Instead, a radio button should be positioned in a container that belongs to a form. The typical container is the group box. When a radio button is added to a group box, the location of the radio button is relative to its parent. This location is easy to specify if you are visually designing the application. If you are programmatically creating it, make sure you specify the location based on the control that will hold the radio button. Here are examples:

```Imports System.Drawing
Imports System.Windows.Forms

Module Exercise

Public Class Starter
Inherits Form

Private grpPizzaSize As GroupBox

Dim components As System.ComponentModel.Container

Public Sub New()
InitializeComponent()
End Sub

Public Sub InitializeComponent()

grpPizzaSize = New GroupBox()
grpPizzaSize.Size = New Size(160, 120)
grpPizzaSize.Location = New Point(20, 10)

End Sub

End Class

Function Main() As Integer

Dim frmStart As Starter = New Starter

Application.Run(frmStart)

Return 0
End Function

End Module
```

This would produce:

 The Caption of a Radio Button

To indicate what a radio button represents, it is accompanied by text, also referred to as its caption. To specify the caption of a radio button at a design time, type a string in the Text field of its Properties window. To programmatically specify the caption of a radio button, assign a string to its Text property. Here are examples:

```Public Sub InitializeComponent()

grpPizzaSize = New GroupBox()
grpPizzaSize.Size = New Size(160, 120)
grpPizzaSize.Location = New Point(20, 10)

End Sub```

This would produce:

The application we are going to create is used to calculate the amount owed on a loan using the following formula:

 P = Principal r = Annual (Interest) Rate m = Number of Compounding Periods per Year n = Total Number of Compounding Periods A = Amount Earned After n periods
1. Start a new Windows Application named CompoundInterest1
2. In the Solution Explorer, right-click Form1.vb and click Rename
3. Type CompoundInterest.vb and press Enter
4. Design the form as followed:

 Control Name Text Additional Properties GroupBox Loan Setup Label Principal: TextBox txtPrincipal 0.00 TextAlign: Right Label Interest Rate: TextBox txtInterestRate 8.25 TextAlign: Right Label % Label Number of Periods: TextBox txtPeriods 1 TextAlign: Text Label years GroupBox Compound Frequency RadioButton rdoMonthly RadioButton rdoQuarterly RadioButton rdoSemiannually RadioButton rdoAnnually GroupBox Results Label Interest Earned: TextBox txtInterestEarned 0.00 TextAlign: Right ReadOnly: True Label Amount Earned: TextBox txtFutureValue 0.00 TextAlign: Right ReadOnly: True Button btnCalculate Calculate Button btnClose Close
5. On the form, double-click the Close button and implement the event as follows:

 ```Private Sub btnClose_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnClose.Click End End Sub```

If you add only one radio button to a container, when the application starts, the lone radio button would appear with an empty round circle. If the user clicks that lone radio button, the radio button's circle becomes filled with a dot and the user cannot remove or change this aspect. If you equip a container with more than one radio button, the user can click the desired one to select it and only one of the radio buttons can be selected at a given time. The radio button that is selected is referred to as checked. To support this description, the RadioButton class is equipped with a property named Checked.

At design time, to select a radio button, in the Properties window, set its Checked property to True. At run time, to programmatically select a radio button, assign a true value to its Checked property. To find out whether a particular radio button is selected, get the value of its Checked property. You can also programmatically check a radio button. Here is an example:

```Public Sub InitializeComponent()

grpPizzaSize = New GroupBox()
grpPizzaSize.Size = New Size(160, 120)
grpPizzaSize.Location = New Point(20, 10)

End Sub```

If the user clicks a radio button, since this control is primarily a button, the radio button that was clicked in the group fires a Click event. This is the most regularly used event of a radio button. Normally, when the user clicks a button in the group, the round box of that button becomes filled and the Click event is fired. If the user clicks a button that is already checked, nothing changes in the round box of that button but the Click event fires again. In some cases, you may want to execute code only if the checked state of a button has actually changed rather than being interested in whether the button was clicked or not. Fortunately, if you are interested only when the checked stated of a button is changed, you can use the CheckedChanged event. This event is fired whenever the checked state of a button is modified.

1. On the form, click Monthly
2. In the Properties window, double-click Checked to set its value to True
3. On the form, double-click the Calculate button and implement its Click() event as follows:

 ```Private Sub btnCalculate_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) _ Handles btnCalculate.Click Dim Principal As Double Dim InterestRate As Double Dim InterestEarned As Double Dim FutureValue As Double Dim RatePerPeriod As Double Dim Periods As Double Dim CompoundType As Integer ' Retrieve the value of the principal Try Principal = CDbl(txtPrincipal.Text) Catch ex As Exception MsgBox("The value you entered for the principal " & _ "is not valid" & vbCrLf & "Please try again") End Try ' Retrieve the interest rate Try InterestRate = CDbl(txtInterestRate.Text) / 100 Catch ex As Exception MsgBox("The value you entered for the interest rate " & _ "is not valid" & vbCrLf & "Please try again") End Try ' Find out what radio button was clicked to apply the compound frequency If rdoMonthly.Checked Then CompoundType = 12 ElseIf rdoQuarterly.Checked Then CompoundType = 4 ElseIf rdoSemiannually.Checked Then CompoundType = 2 Else CompoundType = 1 End If ' Get the number of periods Try Periods = CDbl(txtPeriods.Text) Catch ex As Exception MsgBox("The value you entered for the number of periods " & _ "is not valid" & vbCrLf & "Please try again") End Try ' These values will make the calculation easier to read Dim i As Double = InterestRate / CompoundType Dim n As Double = CompoundType * Periods ' Perform the necessary calculations RatePerPeriod = InterestRate / Periods FutureValue = Principal * Math.Pow(1 + i, n) interestEarned = FutureValue - Principal ' Display the values in the appropriate text boxes txtInterestEarned.Text = FormatCurrency(InterestEarned) txtFutureValue.Text = FormatCurrency(FutureValue) End Sub```
4. Test the application

 The Alignment of a Radio Button

By default, the round box of a radio button is positioned to the left side of its accompanying label but you have many options. Besides the left position, you can position the round box to the top, the right, or the bottom etc side of its label. The position of the round box with regards to its label is controlled by the CheckAlign property which is a value of type ContentAlignment. To specify it at design time, access the Properties window of the radio button and select the desired value from the CheckAlign field. You can also change this property programmatically. Here are examples:

```Public Sub InitializeComponent()

grpPizzaSize = New GroupBox()
grpPizzaSize.Size = New Size(160, 120)
grpPizzaSize.Location = New Point(20, 10)

End Sub```

Besides the alignment of the check box, you can also control the alignment of the text with regards to the bounding rectangle of the control. This characteristic is controlled by the TextAlign property of the RadioButton class. The TextAlign property also is of type ContentAlignment.

 The Appearance of a Radio Button

By default, a radio button appears as a rounded box that gets filled with a big dot when the user selects it. Optionally, you can make a radio button appear as a toggle button. Normally, if you make one radio button appear as a button, you should apply the same characteristics on the other radio buttons of the same group. The button would appear as a rectangular object. When the user clicks such a button, it appears down:

If the user clicks another button, this button becomes up:

To change the appearance of a radio button, assign the Button or Normal value to its Appearance property. The Appearance property is based on the Appearance enumeration. Here are examples:

```Public Sub InitializeComponent()

grpPizzaSize = New GroupBox()
grpPizzaSize.Text = "Pizza Size"
grpPizzaSize.Size = New Size(150, 120)
grpPizzaSize.Location = New Point(20, 10)

End Sub```

This would produce:

As you can see, you can apply the Appearance property to a radio button that does not have a caption. You can also use a caption. If you do, make sure you align the caption to make is good to see. Here are examples:

```Public Sub InitializeComponent()

grpPizzaSize = New GroupBox()
grpPizzaSize.Text = "Pizza Size"
grpPizzaSize.Size = New Size(150, 120)
grpPizzaSize.Location = New Point(20, 10)

End Sub```

This would produce:

If you configure your application and give the user the ability to change the appearance of the radio button from a round circle to a rectangular object and vice-versa, and if the user decides to change this appearance, when this is done, the control whose appearance was changed fires an AppearanceChanged event. The AppearanceChanged event is of type EventArgs, meaning that it does not carry any significant information other than to let you know that the appearance of the button was changed.

 Practical Learning: Using the Appearance of a Radio Button
1. Create a new Window Application named ElementaryOperations1
2. In the Solution Explorer, right-click Form1.vb and click Rename
3. Set the name to Exercise.vb
4. Design the form as follows:

5. Double-click the New Operation button and implement its event as follows:

 ```Private Sub btnNewOPeration_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) _ Handles btnNewOPeration.Click Dim Number1 As Integer Dim Number2 As Integer Dim rndNumber As Random rndNumber = New Random ' If the user clicked the Level 1 button, ' the operation will be performed on numbers from 1 to 9 If rdoLevel1.Checked = True Then Number1 = rndNumber.Next(1, 10) Number2 = rndNumber.Next(1, 10) ElseIf rdoLevel2.Checked = True Then ' If the user clicked the Level 2 button, ' the operation will be performed on numbers from 10 to 19 Number1 = rndNumber.Next(10, 30) Number2 = rndNumber.Next(10, 30) ElseIf rdoLevel3.Checked = True Then ' If the user clicked the Level 3 button, ' the operation will be performed on numbers from 21 to 49 Number1 = rndNumber.Next(30, 50) Number2 = rndNumber.Next(30, 50) ElseIf rdoLevel4.Checked = True Then ' If the user clicked the Level 4 button, ' the operation will be performed on numbers from 51 to 99 Number1 = rndNumber.Next(50, 101) Number2 = rndNumber.Next(50, 101) End If ' Display the numbers to the user lblOperand1.Text = CStr(Number1) lblOperand2.Text = CStr(Number2) ' Just in case, empty the Result text box txtResult.Text = "" ' Give focus to the Result text box txtResult.Focus() End Sub```
6. In the Class Name combo box, select rdoLevel1
7. In the Method Name combo box, select Click and implement its event as follows:

 ```Private Sub rdoLevel1_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles rdoLevel1.Click ' When the user clicks the Level 1 button, ' behave as if the user had click the New Operation button ' That is, behave as if the user wants a new operation btnNewOPeration_Click(sender, e) End Sub```
8. In the Class Name combo box, select rdoLevel2
9. In the Method Name combo box, select Click and implement its event as follows:

 ```Private Sub rdoLevel2_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles rdoLevel1.Click btnNewOPeration_Click(sender, e) End Sub```
10. In the Class Name combo box, select rdoLevel3
11. In the Method Name combo box, select Click and implement its event as follows:

 ```Private Sub rdoLevel3_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles rdoLevel1.Click btnNewOPeration_Click(sender, e) End Sub```
12. In the Class Name combo box, select rdoLevel4
13. In the Method Name combo box, select Click and implement its event as follows:

 ```Private Sub rdoLevel4_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles rdoLevel1.Click btnNewOPeration_Click(sender, e) End Sub```
14. In the Class Name combo box, select rdoAddition
15. In the Method Name combo box, select Click and implement its event as follows:

 ```Private Sub rdoAddition_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles rdoAddition.Click lblOperation.Text = "+" End Sub```
16. In the Class Name combo box, select rdoSubtraction
17. In the Method Name combo box, select Click and implement its event as follows:

 ```Private Sub rdoSubtraction_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles rdoSubtraction.Click lblOperation.Text = "-" End Sub```
18. In the Class Name combo box, select rdoMultiplication
19. In the Method Name combo box, select Click and implement its event as follows:

 ```Private Sub rdoMultiplication_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles rdoMultiplication.Click lblOperation.Text = "*" End Sub```
20. In the Class Name combo box, select rdoDivision
21. In the Method Name combo box, select Click and implement its event as follows:

 ```Private Sub rdoDivision_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles rdoDivision.Click lblOperation.Text = "/" End Sub```
22. In the Class Name combo box, select btnCheckResult
23. In the Method Name combo box, select Click and implement its event as follows:

 ```Private Sub btnCheckResult_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnCheckResult.Click Dim Number1 As Double Dim Number2 As Double Dim UserResult As Double Dim OurResult As Double Dim RandomNumber As Random = New Random ' It is hard to perform a comparison on a division ' So we will have to do some gymastic here to get something ' We will use this variable to format the number ' to appear as 0.00 ' That will allow us to perform the comparision ' on a decimal number with a precision of 2 Dim strFixedResult As String strFixedResult = "" Dim Congratulations As String() = { _ "Right :) - WOW - Good Answer!", _ "Good Answer :) - You are Impressive", _ "Right Answer :) - What a Good Job!", _ "Good :) - You Are Greaaaaaaaaaaaat", _ "Wonderful Answer :) - You Know It" _ } Dim WrongAnswers As String() = { _ "Uhhhhhhhhhh - Bad Answer", _ "Wrong - You will do better next time", _ "Nop", _ "Common - You can do Better Than That!", _ "No - You are probably getting tired" _ } ' Make sure the user provides a result If txtResult.Text = "" Then MsgBox("You must provide a result before clicking the button") Exit Sub End If ' Use exception handling to get the result Try UserResult = CDbl(txtResult.Text) Number1 = CDbl(lblOperand1.Text) Number2 = CDbl(lblOperand2.Text) ' Get the user's answer If rdoAddition.Checked = True Then OurResult = Number1 + Number2 ' Format the result to appear with 2 decimal numbers strFixedResult = String.Format("{0:F}", Number1 + Number2) End If If rdoSubtraction.Checked = True Then OurResult = Number1 - Number2 strFixedResult = String.Format("{0:F}", Number1 - Number2) End If If rdoMultiplication.Checked = True Then OurResult = Number1 * Number2 strFixedResult = String.Format("{0:F}", Number1 * Number2) End If If rdoDivision.Checked = True Then OurResult = Number1 / Number2 strFixedResult = String.Format("{0:F}", Number1 / Number2) End If ' Check if the user's answer is the right one ' Because of the division, we will format the result as 0.00 ' then perform the comparison If strFixedResult = CDbl(txtResult.Text).ToString("F") Then MsgBox(Congratulations(RandomNumber.Next(0, 4)), _ MsgBoxStyle.OkOnly Or MsgBoxStyle.Question, _ "Elementary Operations") Else MsgBox(WrongAnswers(RandomNumber.Next(0, 4)), _ MsgBoxStyle.OkOnly Or MsgBoxStyle.Information, _ "Elementary Operations") End If ' After checking the user's answer, generate a new operation btnNewOPeration_Click(sender, e) Catch ex As Exception MsgBox("Invalid Numeric Value.") End Try End Sub```
24. Execute the application and test it