Visual Basic Programming Guide

of 144 Paul Bolton 2012
Table of Contents
Part 1 - The Basics ...........................................................7
Introduction: Three Steps in Developing a Windows Application ............... 7
Exercise 1.1 - Changing the text in a label control .................................................9
Designing the Form .......................................................................................12
Coding .......................................................................................................13
Running the Program ....................................................................................14
Saving the Program ......................................................................................14
More on the VB Integrated Development Environment (IDE)................. 14
Menu Bar ...................................................................................................14
Toolbox......................................................................................................16
Solution Explorer Window ...............................................................................17
Standard naming conventions for controls ...........................................................19
The Visual Basic 2010 IDE – In depth.............................................. 21
Structure of a Visual Basic Windows Application..................................................22
Part 2 - Moving on from the Basics....................................23
Consolidation exercises introducing Visual Basic ................................... 23
Exercise 2.1 ...............................................................................................23
Exercise 2.2 ...............................................................................................24
Exercise 2.3 ...............................................................................................24
Exercise 2.4 ...............................................................................................25
Part 3 – Arithmetic & Variables.........................................26
Arithmetic Introductory Exercise 3.1............................................... 26
Introduction to data types ............................................................................26
Task 1 ....................................................................................................26
Task 2 ................................................................................................... 27
Task 3 ...................................................................................................28
Observations ............................................................................................28
Arithmetic & Variables: Underpinning Knowledge ................................ 29
Data Types ................................................................................................29
Arithmetic Exercise 3.2 Declaring variables & type casting.....................................30

Task 1 ....................................................................................................30
Task 2 ...................................................................................................33
Task 3 ...................................................................................................33
Task 4 ...................................................................................................34
Arithmetic, Data-Types & Variables ................................................ 35
Converting data before storing it into variables (known as data “ Type Casting”) ........35
Part 4 - More on Arithmetic & Variables.............................36
Arithmetic Exercise 4.1................................................................ 36
Introducing the scrollbar control ......................................................................36
Scrollbar Setting scrollbar properties ............................................... 38
(1) Setting Max and Min properties ................................................................40
(2) Setting SmallCange and LargeChange properties.............................................40
(3) Setting Value property ............................................................................41
Arithmetic Exercise 4.2 – Wallpaper Estimator...................................................43
Data types, arithmetical operators & variables .................................................43
Part 5 - Making selections using If..Then..Else .................48
Program Control – making selections using “If..Then..Else”................... 48
Tax Calculator Program - Scenario ....................................................................51
Part (a) ..................................................................................................51
Part (b).................................................................................................52
Part (c) .................................................................................................52
If…Then…Else - Exercise 5.1 - Tax Calculator......................................................53
If…Then…Else - Exercise 5.2 Tax Calculator Enhancements .....................................58
(a) Using the TabIndex property ..................................................................58
(b) Providing a “Clear” button and improving navigation ....................................58
(c) Protecting data and improving navigation...................................................59
If…Then…Else – Exercise 5.3 Tax Calculator – adding a password form .....................60
Task 1 ....................................................................................................60
Task 2 ....................................................................................................61
Part 6 - More on making selections using If..Then..Else ...........64

Sports Club Membership Fees Program - Scenario .............................. 64
Part (a) – creation of basic program ...............................................................64
Part (b) enhancing basic program to provide a password protection form .................64
Part (c) enhancing basic program to provide a printed receipt ...............................64
Part (d) enhancing basic program to work without a mouse ..................................65
If..Then..Else – Exercise 6.1 Using multiple criteria to make selections .....................65
If..Then..Else – Exercise 6.1 SOLUTION ............................................................66
Part 7 Creating menus using the MenuStrip Control ............... 67
MenuStrip Control.......................................................................67
Exercise 7.1 adding a menu to the Tax Calculator ................................................ 67
Part 8 Making selections using Select Case ........................ 70
Select Case................................................................................70
Exercise 8.1 Demonstration of advantage of Select Case construction........................ 70
Sports Club Membership Fees Program - Revisit of scenario: converting
If..Then..Else to Select Case............................................................ 71
Select Case – Exercise 8.2 Membership fees program revisited ................................71
Select Case - Further theory ......................................................................... 74
Select Case Demonstration of advantage of If..Then..Else construction
over Select Case construction .....................................................76
Select Case – Exercise 8.1 SOLUTION ............................................................... 77
Part 9 - Iterations (loops) using For..Next........................... 78
For…Next loops - underpinning knowledge..........................................78
Background................................................................................................. 78
Example .................................................................................................... 78
For..Next Loops - Exercise 9.1 Beep exercise ....................................................80
For.. Next Loops - Underpinning knowledge (continued) ...................... 82
Counting in steps ........................................................................................82
Counting backwards ......................................................................................82
For.. Next loops - Exercise 9.2 - Mobile phone credits exercise ..............................84
Extended Task ............................................................................................84
For… Next Loops - Quiz .............................................................................86
For… Next Loops - Quiz (Answers) ...............................................................88

Coding solution to Exercise 9.2 For... Next loops - Mobile phone credits exercise
SOLUTION.................................................................................................89
Part 10 - Iterations (loops) using Do..Loops .........................90
Conditional loops ........................................................................ 90
Exercise 10.1 “Do…” loops introductory exercise ..................................................90
Conditional loops continued ........................................................... 93
Exercise 10.2 “Do…” loops exercise: Moving a picture ..........................................93
Task 1 ....................................................................................................93
Task 2 ...................................................................................................94
Task 3 ...................................................................................................94
Part 11 - Debugging, Testing & Error Handling .......................95
Debugging ................................................................................. 95
Exercise 11.1 Sales Department Wage Calculator ..................................................95
Debugging – Exercise 11.1: Sales Department Wage Calculator code ........................... 97
How to write testing documentation .............................................. 99
Design-time errors .......................................................................................99
Run-time errors..........................................................................................99
How to write testing documentation (continued) ............................... 101
Sample Test Plan .......................................................................................103
How to write an Error Report ..................................................... 105
Error Report (action taken to correct errors)................................................... 107
Error Handling .......................................................................... 108
Exercise 11.2 Tax Calculator program revisited ...................................................108
Task 1 ...................................................................................................108
Task 2: Error Handling ............................................................................... 111
Task 2 (continued) – Further study ..............................................................113
Task 3: Exception Handling..........................................................................114
Task 3 (continued) – Further study ..............................................................116
Part 12 - File Handling: Using Sequential Data Files (Text Files)117
File handling.............................................................................. 117
Exercise 12.1: Storing student marks in a Data File .............................................117

Task 1 – writing one record .........................................................................117
Task 2 – reading one record ........................................................................118
Task 3 – writing multiple records .................................................................118
Task 4 – reading multiple records ................................................................120
Part 13 Dialog Controls ................................................... 121
Dialog Controls .......................................................................... 121
Exercise 13.1: Adding the Color Dialog control to a program ..................................121
ColorDialog Customisation ...........................................................................122
Exercise 13.2: Adding Open / Save File Dialogs to the “Student Marks” program ......124
(1) Customising the dialog box display .............................................................126
(a) Setting the default filename .................................................................126
(b) Filtering the list of file types................................................................128
(c) Setting the default file location (folder) ..................................................128
(d) Setting the title................................................................................129
(2) Dealing with errors ...............................................................................129
(a) Errors when clicking the “Cancel” button .................................................129
Exercise 13.3: Adding Save File Dialog to the “Student Marks” program .................132
Code for the SaveFile dialog control:.............................................................134
Additional customisation ............................................................................134
Part 14 - Listbox & Combobox controls...............................136
List & Combo Box ..................................................................... 136
Exercise 14.1 Flight Seat Planner....................................................................136
List & Combo Box ..................................................................... 139
Exercise 14.2: Flight Seat Planner enhancement .................................................139
Task 1 ...................................................................................................139
Task 2 ..................................................................................................139
Task 3 ..................................................................................................139
Part 15 Multiple Event Handlers........................................ 141
Multiple Event Handlers............................................................... 141
Exercise 15.1: Colour Picker ............................................................................141

Part 1 - The Basics
Introduction: Three Steps in Developing a Windows Application
The Visual Basic Integrated Development Environment (IDE)
Makes building an application a straightforward process. There are three
primary steps involved in building a Visual Basic application:
1. We draw the user interface by placing
controls on a Windows form
2. We assign properties to controls
3. We write code for control events (and perhaps write other procedures)
Example
Example

These same steps are followed whether you are building a very simple
application or one involving many controls and many lines of code.
The event-driven nature of Visual Basic applications allows you to build your
application in stages and test it at each stage. You can build one procedure,
or part of a procedure, at a time and try it until it works as desired. This
minimises errors.
Example

Exercise 1.1 - Changing the text in a label control
- Go to the Start Menu on the computer
- Find Microsoft Visual Studio 2010
- Select Microsoft Visual Studio 2010 from the sub menu
Once Visual Basic has opened select File / New Project from the menu
Change the name of your
application to
LabelMessageYourName.
So if your name is John Smith
you would name your
application
LabelMessageJohnSmith
Visual Studio will now load. This may take a
few minutes, BE PATIENT. If you are asked
which settings you would prefer, select
Microsoft Visual Basic.
Leave the template type
selected as Windows Forms
Application.

(no spaces between the words).
Click OK

You should now see the Visual Basic design environment appear similar to the screen
shown below.
Take a few moments to familiarise yourself with the various features before
continuing the exercise. If your screen does not look like the one shown below, tell
your teacher.
Tip: to make the windows stop disappearing, click the drawing pin symbol at
the top of each window then becomes
Click these two icons to alternate
between the Form1 Design window
and the Code window
Solution Explorer windowControls Toolbox Menu
Properties window
Error List window
Form Design
window
Exercise 1.1 (continued)

The Form Designer Window is, as the name implies, where you design your
visual interface. You can add controls from the Toolbox, on the left, onto
your form.
The title bar area shows you the name of your project and the name of the
form currently displayed. Also shown in brackets is one of three words:
Design, Run or Break. This shows the mode Visual Basic is operating in.
Visual Basic operates in three modes.
 Design mode - used to build application
 Run mode - used to run the application
 Break mode - application halted and debugger is available
We focus here on the design mode. You should, however, always be aware of
what mode you are working in.
Now continue with Exercise 1.
The finished program can be seen here:
Designing the Form
1. Make sure Form 1 is selected and in the properties window change the Text
property of the form to Change a message.
lblMessage
This button
has been
clicked to
display the
message above
btnGoodMessage
btnBadMessage
How the program will work: When a button is clicked the message “I LIKE Visual Basic”
appears. When a second button is clicked the message changes to “I HATE Visual Basic”
I LIKE Visual Basic

2. Click on the Label control in the toolbox, and then with the mouse draw a
rectangle in the upper part of the form (by holding down the left mouse button
and dragging the mouse).
3. Find the label’s Name property in the Properties window and change it from
Label1 to lblMessage, using the prefix ‘lbl’. Note that this prefix begins with the
letter ‘l’for lion and not the number 1.(one)
4. Set the label’s Text property to blank by deleting the default value “Label1".
5. The default value for the label’s BorderStyle property is None, meaning that it
has no border will be shown when the program runs. To get the sunken border
effect in the illustration, change this to Fixed3D.
6. Set the label’s Font property to 14 Bold.
7. Set autosize to false
8. Set size width to 200 and height to 50
9. Drag a button from the Toolbox and draw a rectangle at the bottom left of the
form. Set its Text property to Good Message. Change its Name property to
btnGoodMessage. Now place a second button at the bottom right of the form.
Set its Text property to Bad Message. Change its Name property to
btnBadMessage.
Coding
10.Double-click on the Good Message button and you’ll see the code template for its
Click() event as shown below.
The words after the brackets, Handles btnGoodMessage.Click, shows that the code
you are about to write will be executed if the btnGoodMessage is clicked when
the program is running. The code template plus any code that is written inside
the template, is known as an event procedure.
11. Type the line of code below to set the Text property of the label to the
message you wish to display in the label.

12. Return to the form either by clicking the Form1.vb [Design] Page tab or the
View Designer button in the Solution Explorer’s small toolbar (you will need to
hover the mouse over the button to see its name.
13. Double-click the Bad Message button on the form. Type in a line of code similar
to that in step 10 to display the “I do not like Visual Basic” message when the
Bad Message button is clicked.
Running the Program
14. Click the Start button on the toolbar or select Debug/Start from the menu.
Click on each of the two buttons to check that the message changes. Close the
program by clicking the red “X” in the top-right corner of the program window
(i.e. the “form” you created)
Saving the Program
15. Click the icon on the menu. In the Save Project window you should see
LabelMessage automatically displayed as the application name. Don’t alter any of
the entries. Just click the Save button.
More on the VB Integrated Development Environment (IDE)
Menu Bar
Under the title bar is the Menu. This menu is dynamic, changing as you try to do different
things in Visual Basic .NET. When you start working on a project, it should look like this:
You will become familiar with each menu topic as you work through the course. Briefly, they
are:
File Use to open/close projects and files. Use to exit Visual Basic .NET
Edit Used when writing code to do the usual editing tasks of cutting, pasting, copying and
deleting text
View Provides access to most of the windows in the Integrated Development Environment
(IDE)
Project Allows adding files and objects to your application
Build Allows you to compile and run your completed application (go to Run mode)
Debug Comes in handy to help track down errors in your code (works when Visual Basic .NET
is in Break mode)
Background information

Team Ability to work in a Team Foundation Server
Data Used when building database applications
Format Useful for manipulating controls placed on your forms
Tools Allows custom configuration of the IDE. Be particularly aware of the Options choice
under this menu item. This choice allows you to modify the IDE to meet any personal
requirements.
Test Used for testing and debugging your applications
Window Lets you change the layout of windows in the IDE
Help Perhaps, the most important item in the Menu. Provides access to the
Visual Basic on-line documentation via help contents, index or search.
The View menu also allows you to choose from a myriad of toolbars available in the Visual
Basic .NET IDE. Toolbars provide quick access to many features. The Standard (default)
toolbar appears below the Menu:
New project
Open file
Save all
Undo, Re-do
Move backward / forward
Build configuration
View Solution Explorer Window
View Properties Window
View Object Browser
View Toolbox
Team Explorer Window
Start Page
Extensions
Command Window
If you forget what a
toolbar button does,
hover your mouse cursor
over the button until a
descriptive tool tip
appears.
We will discuss most of
these toolbar functions in
the remainder of the IDE
information.

Toolbox
The Toolbox is the selection menu for controls used in your application. It is active when a
form is shown in the design window.
The tools you will use
most are found under
the Windows Forms tab.
Use the scroll arrows to
scroll up and down the
full list of controls.
Many of these tools will
look familiar to you.
They are used in a wide
variety of Windows
applications you have
used (the Visual Basic
IDE even uses them!)
We will soon look at how
to move a control from
the toolbox to a form.
Background information (continued)

Solution Explorer Window
Two other windows (not illustrated) which are useful when running an application are the
Task List Window and Output Window. The task list window highlights any errors
encountered while trying to run an application.
The window will direct you to the line(s) of code with identified errors. The output window
outlines the steps followed as an application is compiled.
The Solution Explorer Window displays a
list of all forms, modules and other files
making up your application. To view a
form in this window, simply double-click
the file name. Or, highlight the file
and press <Shift>-<F7>.
Or, you can obtain a view of the Form
or Code windows (window containing the
actual Basic coding) from the Project
window, using the toolbar near the top
of the window. As we mentioned,
there are many ways to do things using
the Visual Basic IDE.
The Properties Window is used to establish design
mode (initial) property values for objects
(controls). The drop-down box at the top of the
window lists all objects in the current form.
Two views are available: Alphabetic and Categorized
(selection is made using menu bar under this box
are the available properties for the active
(currently selected) object.
Help with any property can be obtained by
highlighting the property of interest and pressing
<F1>.

Standard naming conventions for controls
List continued on next page
lbl...
btn...
txt...
mnu...
chk...
rad...
grp...
pic...
pnl...
dgd...
lst...
cbo...
hsb...
vsb...
tmr...
lblDisplay
btnEnter
txtInput
mnuEditPaste
chkBold
radYellow
grpFontSize
picLogo
pnlFontStyle
dgdEmployees
lstAge
cboFavoriteFood
hsbWidth
vsbHeight
tmrAnimate
Type of control Prefix Example
We name controls using the first 3 letters (the prefix) written in lowercase to represent what
type of control it is. A list of prefixes is shown below. The rest of the name can be any
meaningful word or combination of words representing what the control does. There must be
no gaps in the name. We therefore start each word after the prefix with a capital letter.
This is known as “camel-case”, because the middle of the name has taller (capital) letters, like
the humps of a camel.
For more information on Visual Basic naming conventions, go to:
http://www.akadia.com/services/naming_conventions.html
and scroll to the bottom of the page and find the heading: “12) Visual Control Type
Notation”

We usually give
dialogue controls these
standard names rather
than use different
names for different
applications – as we
do with the other
controls. This is
because there is
usually only one dialog
control of each type
on any of our forms.
dlgOpenFile
dlgSaveFile
dlgFont
dlgColor
dlgPrint
dlgPrintPreview
Type of control Prefix AND Example (see explanation below)

The Visual Basic 2010 IDE – In depth
Visual Basic is an integrated development environment within the Visual Studio. Net
Framework. The visual environment is used to design, develop, debug and deploy Windows
Forms and Web Forms applications. These applications can also be used to integrate database
applications. The major advantage of this new environment is that multi-language applications
can be used over the Internet, thus creating, in theory, a truly open application platform.
In summary the visual studio has the following features:
1. Windows Forms Designer. A graphical design surface for creating GUI. You can drag &
drop controls onto forms.
2. Tools for Windows Forms. A Windows Forms Designer, A Windows Application Template
(e.g. windows or database application etc.), project references and generated starter
code for the applications.
3. Tools for Web Forms. A Web Forms Designer, an ASP.Net Web Application template,
project references and generated starter code.
4. Tools for XML (eXtendible Markup Language) Web Services. A generalised web language
can be generated from your .net application solution file.
5. Multiple language Support. A range of language such as C# and VB.net can used in the
same application or solution. The environment now has Object-Oriented Programming
(OOP) capabilities.
6. Data Access. Components for creating applications that share data, visual database
applications for accessing data using the ADO.NET classes.
7. Error handling. Has a range of debugging tools, classes and objects to find and fix
errors within your application.
8. Wizards. Help you create common and complex tasks, by choosing options, configuring
settings and customising projects.

Structure of a Visual Basic Windows Application
We want to get started building our first Visual Basic Windows application. But, first we
need to define some of the terminology we will be using. In Visual Basic .NET, a Windows
application is defined as a solution.
A solution is made up of one or more projects. Projects are groups of forms and code that
make up some application. In most of our work in this course, our applications (solutions)
will be made up of a single project. Because of this, we will usually use the terms
application, solution and project synonymously.
Thus an Application (Project) is made up of:
 Forms - Windows that you create for user interface
 Controls - Graphical features drawn on forms to allow user interaction (text boxes,
labels, scroll bars, buttons, etc.) (Forms and Controls are objects.)
 Properties - Every characteristic of a form or control is specified by a property.
Example properties include names, captions, size, colour, position, and contents. Visual

Basic .NET applies default properties. You can change properties when designing the
application or even when an application is executing.
 Methods - Built-in procedures that can be invoked to impart some action to a
particular object.
 Event Procedures - Code related to some object or control. This is the code that is
executed when a certain event occurs. In our applications, this code will be written in
the BASIC language
 General Procedures - Code not related to objects. This code must be invoked or called
in the application.
 Modules - Collection of general procedures, variable declarations, and constant
definitions used by an application.
Part 2 - Moving on from the Basics
Consolidation exercises introducing Visual Basic
Exercise 2.1
 Start a new project.
 Create a form with two labels.
Exercises 2.1 to 2.4
Visual Basic uses a very specific directory structure for
saving all of the components for a particular application.
When you start a new project (solution), you will be
asked for a Name and Location (folder / directory).
A folder named Name will be established in the selected
Location. That folder will be used to store all solution
files, project files, form and module files (vb extension)
and other files needed by the project.
Two subfolders will be established within the Name
folder: bin and obj. The bin folder contains your
compiled application (the actual executable code or exe
file). Later, you will see that this folder is considered
the ‘application path’ when ancillary data, graphics and
sound files are needed by an application. The obj folder
contains files used for debugging your application as it is
being developed.

 When the program runs display your name in label 1 and your address in label 2
by using the Form_Load() event. (Double-click on the grey area of the form at
design time display the code window for this event.)
Exercise 2.2
 Place a button on a form. When it is clicked the title bar of the form should
display Welcome to Visual Basic .NET.
Exercise 2.3
Public ClassForm1
Private SubForm1_Load(...) HandlesMyBase.Load
lblName.Text = "MyName"
lblAddress.Text = "MyAddress"
End Sub
End Class
Public ClassForm1
Private SubbtnWelcome_Click(sender As System.Object, e As
System.EventArgs) Handles btnWelcome.Click
Me.Text = "Welcome to Visual Basic .NET"
End Sub
End Class

 Place two buttons on a form and set their Text properties to Show and Hide
respectively using the Properties Window.
 Place a label on the form and set its Visible property to False (which means it
will be invisible when the program first runs).
 Clicking the Show button should make the label visible and display the message
Hello inside it. Clicking the Hide button should remove the label and its message.
(Note: When you set the Visible property in code you do not need quotation
marks around the True or False.)
Exercise 2.4
 Write a program with a label and two buttons.Label width:200 height: 100
 Clicking the ForeColour button displays the message shown in a blue colour.
Clicking the BackColour button displays a different message and colours the rest of
the label yellow. Note that the message is centred within the label. Use the
label’s ForeColor and BackColor properties. To set these properties write
Color.Blue or Color.Yellow to the right of the assignment statement ( = ).
Public ClassForm1
Private SubbtnShow_Click(sender As System.Object, e As System.EventArgs)
HandlesbtnShow.Click
lblHello.Visible = True
lblHello.Text = "Hello"
End Sub
Private SubbtnHide_Click(sender As System.Object, e As System.EventArgs)
HandlesbtnHide.Click
lblHello.Visible = False
lblHello.Text = "Hello"
End Sub
End Class
Public ClassForm1
Private SubbtnForeColour_Click(sender As System.Object, e As System.EventArgs) Handles
btnForeColour.Click
lblColour.Text = "MyForeColour propertyis set to blue"
lblColour.ForeColor = Color.Blue
End Sub
Private SubbtnBackColour_Click(sender As System.Object, e As System.EventArgs)Handles
btnBackColour.Click
lblColour.Text = "MyBackColour propertyis set to yellow"
lblColour.BackColor = Color.Yellow
End Sub
End Class

Part 3 – Arithmetic & Variables
Arithmetic Introductory Exercise 3.1
Introduction to data types
We are going to look at how we can use the properties of controls to transfer
information (data) from one control to another. The program we are about to
create will enable us to:
(1)assign a new BackColor property value (yellow) to a textbox on the left of
the form by copying the existing BackColor property value from a textbox on
the right
(2) assign a new Text property value to a textbox on the left of the form
by copying the existing Text property value from a textbox on the right
(3) assign a new Text property value to a textbox on the left of the form
by copying the existing Text property values from two textboxes on the right.
We will see if we can get two numbers to add up using this technique (a
simple maths calculation).
Task 1
Open a new Windows Application project and create a form like the one illustrated:
txtCopiedColour
txtCopiedText
txtResult
btnCopyColour btnCopyText
txtOriginalColour
txtOriginalText
Exercise 3.1

At design-time, set the BackColor property of txtOriginalColour to yellow (select this
from Custom on the BackColor property list).
Double-click on the Copy Colour button. The code window should open revealing the
template code for this button procedure ready for us to write code into. Write the
following code shown in bold:
Run your program, click the Copy Colour button an see if the yellow colour appears
in the first textbox.
If so, we have successfully assigned a new value to the BackColor property of the
textbox on the left of the form by copying the existing BackColor property value
from a textbox on the right.
Task 2
Now see if you can complete the line of code for the next button, as shown below:
Run your program again, write your name in the txtOriginalText textbox on the
right, click the Copy Text button and see if your name appears in the txtCopiedText
textbox on the left.
Public ClassForm1
Private SubbtnCopyColour_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs)HandlesbtnCopyColour.Click
txtCopiedColour.BackColor = txtOriginalColour.BackColor
End Sub
End Class
btnAdd txtFirstNumber txtSecondNumber
Private SubbtnCopyText_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs)HandlesbtnCopyText.Click
txtCopiedText.Text = .
End Sub
Exercise 3.1

Task 3
Repeat the process with the final button (“Add”). See if you can complete the line
of code below:
Run your program again, write your 2 whole numbers in the txtFirstNumber and
txtSecondNumber textboxes on the right (e.g. 2 + 2), click the Add button and see
if the correct answer appears in the txtResult textbox on the left.
Observations
Try to answer the following questions:
 what result did you get in txtResult?
 how do you think VB is processing the data you have input?
 what data type do you think VB has assumed the number “2” is?
Now look at the handouts / tutorials on data types and converting data types
(“type-casting”) and see if you can work out what must be added to your code to
cure the problem we are encountering.
Private SubbtnAdd_Click(ByValsender As System.Object, _
ByVal e As System.EventArgs)HandlesbtnAdd.Click
txtResult.Text = .
End Sub

Arithmetic & Variables: Underpinning Knowledge
Data Types
Data Type Usage
Size
(1 byte = 8 bits)
To store numeric data
Short (or Int16)
(“Shortinteger”)
Wholenumbersonly
Can hold whole numbers(positiveor negative) between
approx +32,000 to -32,000
2 bytes
(i.e. 16 bits)
Integer (or Int32) Can hold whole numbers(positiveor negative) between
approx +2 billion to -2 billion (i.e. +2 followed by 9 zeros
or -2 followed by 9 zeros)
4 bytes
(i.e. 32 bits)
Long(or Int64)
(“Long integer”).
Can hold whole numbers(positiveor negative) between
approx +9 (followed by18 zeros) to -9 (followed by18
zeros)
8 bytes
(i.e. 64 bits)
Single
(“Single-precisionfloating-
point”)
WholeORdecimalnumbers
Can hold whole numbersORnumberscontaininga
decimalpoint (positiveor negative) Therangeof values
which can bestored forpositivenumbersis
approximately:+3 (followed by38 zeros) for verylarge
values, to +0.0 (followed by45 zerosand then 1) for very
small values. For negativenumbers,therangeis
approximately:-3 (followed by38 zeros) for verylarge
values, to -0.0 (followed by45 zerosand then 1) for very
small values.
4 bytes
Double
(“Double-precision floating-
point”)
Can hold whole numbersORnumberscontaininga
decimalpoint (positiveor negative) Therangeof values
which can bestored forpositivenumbersis
approximately:+1 (followed by308 zeros) for verylarge
values, to +0.0 (followed by324 zerosand then 4) for
verysmallvalues. For negativenumbers,therangeis
approximately:-1 (followed by308 zeros) for verylarge
values, to -0.0 (followed by324 zerosand then 4) for
verysmallvalues.
8 bytes
Decimal Can hold numberscontainingadecimalpoint (positive
or negative) between approx
+7 (followed by28 zeros) to -7 (followed by28 zeros)
16 bytes
To store other data
Boolean
Otherdata
Used to hold True or False 2 bytes
Date Can hold datesfromJanuary1,0001to December 31,
9999,and timefrom00:00:00to 23:59:59
8 bytes
String
Used to hold characters(e.g.all theletters & symbolson
the keyboard and numbers 0-9,butNOTif thenumbers
are to be used in calculations).
Variable size
Object
An object variable holds a referenceto an object,notthe
objectitself. Thereforethe variableonlyneeds a small
amountof memory. In theory,any data typecan be
stored in an objectvariable.
4 bytes

Arithmetic Exercise 3.2 Declaring variables & type casting
Task 1
We are going to
create a simple
calculator. Open a
new Windows
Application project
and create a form
like the one
illustrated:
Give the buttons suitable names (e.g. btnAdd, btnSubtract etc.). Give the
textboxes the names txtFirstNumber, txtSecondNumber and txtResult respectively.
Double-click on the Add button. The code window should open revealing the
template code for this button procedure ready for us to write code into:
Move the cursor and insert it between the line: Public Class Form1 and the line:
Private Sub btnAdd_Click(…) and then write the following code:
Public ClassForm1
|
End Sub
End Class
Cursor
Public ClassForm1
'declare variables
Dim intFirstNumber As Integer
Dim intSecondNumber As Integer
Dim intResult As Integer
End Sub
End Class
Cursor
Exercise 3.2

You will notice that the above process is in 3 main steps:
(1) Input (where the numbers typed by the user are stored into variables)
(2) Calculation (where we use the variables to do the arithmetic)
(3) Output (where we display the result into a text box)
This is a sequence we will use again and again in our programming projects.
We have declared three variables of Integer type – intFirstNumber, intSecondNumber
and intResult. We want the program to accept two whole numbers (integers) in
txtFirstNumber and txtSecondNumber and then perform the calculations indicated by
the buttons.
In order to do this we need to:
(1) store the two values which the user has typed into txtFirstNumber and
txtSecondNumber into our variables intFirstNumber and intSecondNumber.
(2) do the arithmetic and then store the result into the variable intResult.
(3) display the result. For this we need to change the .Text property of
txtResult to the value held in intResult.
Add the code below to the _Click() event procedure of btnAdd:
HINT
Public ClassForm1
'declare variables
'INPUT
'load contents of 1st textbox into 1st variable
intFirstNumber = txtFirstNumber.Text
'load contents of 2nd textbox into 2nd variable
intSecondNumber = txtSecondNumber.Text
'CALCULATION
'add 2 variables and load result into 3rd variable
intResult = intFirstNumber + intSecondNumber
'OUTPUT
'display contents of 3rd variable in 3rd text box
txtResult.Text = intResult
End Sub
End Class
Exercise 3.2

Run you program, enter two numbers and click the add button. See if the correct
answer appears in txtResult.
Task 2
We have relied upon Visual Basic automatically converting data into the appropriate
data types for us. For example, it took the text from the first textbox (a String
data-type) and converted it into an Integer before adding it to the second number.
This is data-type conversion is known as type casting.
We are now going to do this with functions in our code.
Add the following statement to the top of your code:
You will immediately see parts of the code underlined in blue and errors appear in
the Error List Window.
To solve this problem we need to convert the data-type of the numbers from String
to Integer in the first button (btnAdd) by including the conversion function CInt().
Amend you code as follows:
Run your program, enter two numbers and click the add button. See if the correct
answer appears in txtResult.
Task 3
So far we have used the + operator to add the two numbers together. The other
operators that we can use are:
Option Strict On
Public ClassForm1
'declare variables
End Sub
End Class
'INPUT
'load contents of 1st textbox into1st variable
intFirstNumber = CInt(txtFirstNumber.Text)
'load contents of 2ndtextbox into2ndvariable
intSecondNumber = CInt(txtSecondNumber.Text)
Exercise 3.2

+ Add
- Subtract
/ Divide
* Multiply
MOD Modulus
^ Raise to the power of
Now add sections of code to perform the correct arithmetic for each of the buttons
shown in the example.
(Note: we cannot use the % symbol to calculate percentages. Instead we must
divide the first number by the second number and then multiply by 100.)
Task 4
Cint() is a function that converts text, provided it is a numeric, to Integer data
format. There are other function like this. To find out about them read the
Background Information on the next page. (If Online Help is available on your
computer, you can also highlight CInt() and then press the F1 key.)
Test your program with numbers like 350 and 260.You will get overflow.
Now try using Long instead of Integer in your Dim statements. You will need to
change the CInt() functions to CLng()
Try dividing 13 by 2. You won’t get the right answer. Use Single instead of Long
in your Dim Statements. (Again you will have to change the conversion function –
use the help facility to look up what you need to use or read the next page on this
subject.)
Exercise 3.2

Arithmetic, Data-Types & Variables
Converting data before storing it into variables (known as data “Type
Casting”)
So far we have looked at how to declare a variable and store data into it. For
example, suppose our user is going to type the number “123” into a text box called
txtFirstNumber. We want to write code which will store this number into a variable
called intFirstNumber and then do a maths calculation with it. To do this we would:
(1)declare the variable:
(2) then store the data into it by writing:
intFirstNumber = txtFirstNumber.Text
But this does not actually convert the string “123” into numbers which our program
can use to do maths with. Remember that because the number is in a text box,
Visual Basic does not automatically recognise that this is a number. It assumes the
number is a series of characters (a “string”) like a telephone number or bank account
number. If we try to get VB to add 1 to this string, we will probably get the
answer 1231 instead of 124. VB will simply put the 1 on the end of 123 like a
putting letter on the end of a word.
Declaring a variable as an Integer type does not convert the data to an integer, it
simply puts a “filter” over the variable so that it refuses to accept anything but an
integer! So if we try to store the decimal number 0.75 into it we will simply get
an error message.
Therefore we need to use a function to convert the data in the text box into the
correct data type before we try to store it into the variable. To do this we use
one of the following data type conversion functions, for example:
Numeric data types:
CShort( ) to convert to Short data type
CInt( ) to convert to Integer data type
CLng( ) to convert to Long data type
CSng( ) to convert to Single data type
CDbl( ) to convert to Double data type
CDec( ) to convert to Decimal data type (used especially for currency data)
Otherdata types:

CBool( ) to convert to Boolean data type (True / False)
CDate( ) to convert to Date / Time data type (e.g. #17/10/06 13:50:02#)
CStr( ) to convert to String data type (e.g. "My name is John")
For example, to convert the string “123” contained in text box txtFirstNumber into
an integer and then store it into our variable, we would write:
intFirstNumber = CInt(txtFirstNumber.Text)
We need to be careful however, because if the data doesn’t exactly match the data
type, VB will do its best to convert it anyway. For example, if we write the above
code and the user writes the string 12.75 into the text box, the integer 13 will be
stored in the variable intFirstNumber. In other words the 0.75 part of the number
will simply be rounded up to the next whole number. (Note: if we actually wanted
to store decimal numbers we would need to declare the data type of our variable as
a single and use the conversion function CSng() instead.)
Part 4 - More on Arithmetic & Variables
Arithmetic Exercise 4.1
Introducing the scrollbar control
Create a form like the one above.
The aim of the program is to allow the user to convert temperatures from Farenheit
into Celsius by moving the scroll bar. The Farenheit temperature values will range
from –60 to +120. (Moving the scroll bar thumb upwards should increase the
temperature values.) Set the initial Text property of txtTempF and txtTempC to
32 and 0 respectively, and the Value of the scroll bar to 32.
txtTempF txtTempC
vsbTemperature
Exercise 4.1

(a) From the above information work out what the Min and Max property values of
the scroll bar should be. (Remember that for vertical scroll bars the Min property
always corresponds to the topmost position of the thumb!)
(b) Write code into the scrollbar _Scroll(...) event which will take the Farenheit
value displayed in txtTempF, convert it to Celsius and display it in txtTempC. The
conversion formula is:
Celsius = (Farenheit – 32) x 5
/9
Public ClassForm1
Dim intTempF As Integer 'declare variables
Dim intTempCAs Integer
'----------------------------------------------------------------------------
Private SubvsbTemperature_Scroll(ByVal sender As System.Object, _
ByVal e As System.Windows.Forms.ScrollEventArgs)HandlesvsbTemperature.Scroll
'store value of scrollbar intoF variable
intTempF= vsbTemperature.Value
'convert F value to stringanddisplayinF textbox
txtTempF.Text = CStr(intTempF)
'calculate Cvalue, convert to integer and store inCvariable
intTempC= CInt((intTempF - 32) * 5 / 9)
'convert Cvalue to string anddisplayin Ctextbox
txtTempC.Text = CStr(intTempC)
End Sub
'-------------------------------------------------------
End Class
Scroll bar property settings
required to achieve full
temperature range displayed:
Vertical scroll bar
(vsbTemperature)
Min:120
Max:-60
Small change:1
Large change:10
Value:32

Scrollbar Setting scrollbar properties
A scroll bar returns a numeric value depending on the position of the slider or
(“thumb”).
Scroll bars are quite complex because they have 5 main properties to set and 2
events to code in order for them to work properly.
The 5 properties are listed below:
Property Horizontal
ScrollBar
Vertical
ScrollBar
Max the value returned when the slider
is at the right hand end of the
ScrollBar
The value returned when the slider
is at the bottom of the ScrollBar
Min the Value returned when the slider
is at the left hand end of the
ScrollBar
The Value returned when the slider
is at the top of the ScrollBar
Large Change The amount by which the Value property is changed when the user
clicks on the grey area between the slider and either end of the
ScrollBar.
Small Change The amount by which the Value property is changed when the user
clicks on the arrows at either end of the ScrollBar
Value This returns an integer which indicates the position of the slider in
terms of the range set by Max and Min.
slider or “thumb”
clicking here
affects
SmallChange
property
clicking here
affects
SmallChange
property
clicking here
affects
LargeChange
property

(1) Setting Max and Min properties
We set Max and Min to suit the application we are using. For example, if we
wanted to use a scroll bar to input the temperature of a pan of water in degrees
Celsius we would set the Min property to 0 and the Max property to 100 to
correspond to the freezing and boiling point of water. When you first draw a scroll
bar on your form the default value of Min is 10 and Max is 100. Note that with
vertical scroll bars, the Min value is always returned when the thumb is at the top.
Therefore it is quite common for the Min value to be set greater than the Max
value when using vertical scroll bars.
(2) Setting SmallCange and LargeChange properties
There are no rules governing what values you should set the SmallChange and
LargeChange properties to. However, by default the SmallChange property is set to 1
when you first draw the scroll bar, and the LargeChange property is set to 10. This
means that if the range of the scrollbar (i.e. the Max value minus the Min value) is
quite large the thumb will move incredibly slowly when the user clicks on the arrows.
Therefore it is very important that you set these properties to values which will give
reasonable travel of the thumb.
As a rough guide, set the LargeChange property to one tenth of the range value, and
set the SmallChange property to one tenth of the LargeChange property.
Note: The ratio of LargeChange property to the range also affects the length of the
thumb. The thumb is lengthened to restrict the distance it travels, as shown in the
diagram below: In this example the Min property is set to 0 and the Max is 100,
meaning that the range is 100. If the LargeChange property is left at the default
value of 10, the thumb remains quite small. However, if the LargeChange property is
increased to 50, the size of the thumb increases to one third the length of the
scroll bar, since it only requires 2 clicks to move the thumb to its maximum value.
(The value is taken from the position of the left edge of the thumb.)
Size of the thumb when LargeChange property is set to 1:Min = 0
Max = 100

Size of the thumb when LargeChange property is set to 50 on the same scroll bar:
(3) Setting Value property
This is the initial value of the scroll bar at run-time, and hence determines the
initial position of the thumb. The Value property must be within the range of the
Max and Min properties. Often the Value property will be the same as the Min
property so as to put the thumb at one end of the scrollbar, but this is not always
the case.
Scrollbars
Summary of features
 The purpose of a scrollbar is to generate numbers
which we can use elsewhere in our program
 We can use these numbers to:
o change the value of properties of other
controls
o perform calculations
 We use the scrollbar’s value property as the source of these numbers
 As the user clicks the scrollbar arrows (or drags the scrollbar slider) the value of
the scrollbar changes
 We control what range of values will be generated by setting the Max and Min
properties of the scrollbar at design time
 We can decide where the position of the slider is when the program first opens
by setting the scrollbar’s value property at design time (but this initial value
must lie somewhere between the Max and Min values)
Min = 0 Max = 100
(position allows for width of
thumb)

 We can decide how quickly the value of a scrollbar changes when the user clicks
the scrollbar arrows (or drags the scrollbar slider). We do this by setting the:
o SmallChange and
o LargeChange properties
 (As a guide, set the LargeChange property to 1/10th
the value of the Max
property, and set the SmallChange property to 1/10th
the value of the
LargeChange property)
 when the user clicks the scrollbar arrows or drags the scrollbar slider it fires the
_Scroll(...) event

Arithmetic Exercise 4.2 – Wallpaper Estimator
Data types, arithmetical operators & variables
In this exercise we will be revising what we have covered so far on:
 data types
 converting data to different types (known as “type casting”)
 declaring variables of appropriate data types
 arithmetical operator precedence using the common operators:
Your task is to estimate the amount of wallpaper required to cover the wall
illustrated below which has one window.
The wallpaper comes in rolls 0.7 metres wide and 10 metres long.
Cost per roll is £8.00
Your task is to calculate and display:
4.5m
3m
4.5m2.5m
1.5m
Area A Area B
Area C
Area D
0.5m
Order of precedence:
(1)( ) brackets (parentheses)
(2) ^ exponentiation (“power of”)
(3) + - positive & negative signs
(4) * / multiplication & division
(5) integer division (gives only whole number result of
Exercise 4.2

 the number of rolls required
 the total cost of wallpaper
 the relative cost of wasted wallpaper left over from the last full roll (e.g. if
half a roll was left over, we could say that £4.00 worth of wallpaper was
wasted)
Assume the wallpaper pieces can be pasted in any sequence / orientation irrespective
of where the joins occur, and that there is no wastage due to overlap or off-cuts.
In other words, assume the total area of one roll covers exactly the same amount of
area of the wall.

(1) Find total area of wall
Here are some tips on how to calculate the total area of the wall. After reading
the tips, try to create one line of code in your program which uses all the
measurements and stores the answer in a variable sngWallArea.
Area A:
height * width
3m * 4.5m = 13.5 square meters
Area B is the same, so multiply the area of A by 2
Area C:
height * width
0.5m * 2.5m = 1.25 square meters
Area D:
We haven’t been told the height but we can work it out by subtracting
the height of the window plus the height of Area C from the height of
the room. Once we have found this we multiply height * width as
usual to find the area of D.
Finally, Total Area = Area A + Area B + Area C + Area D
Here is the start of the code you will need. The figures calculating Areas A & B
have been written for you already. See if you can finish off the line. Be careful to
remember the rules about operator precedence and use parentheses (brackets) if
necessary:
sngWallArea = ((3 * 4.5)*2) +
(2) Find area of one roll of wallpaper
Area of one roll = length * width
= 10 * 0.7
= 7 square meters
Again, here is the start of the code you will need:

sngOneRollArea =
(3) Find number of whole rolls needed
(4) (a) Find area of wallpaper roll left over
(4) (b) Find length of wallpaper roll left over
(5) Find cost of total wallpaper rolls purchased
(6) Find relative cost of fraction of wallpaper roll left over

Public ClassForm1
Dim sngWallArea As Single
Dim sngOneRollArea As Single
Dim intNoOfRolls As Integer
Dim sngRemainderAreaOfRoll As Single
Dim sngRemainderLengthOfRoll As Single
Dim decCostOfWallpaperPurchased As Decimal
Dim decCostOfWallpaperWasted As Decimal
Private SubbtnCalculate_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnCalculate.Click
'(1) calculate total area of wall
sngWallArea = ((3 * 4.5) * 2) + (0.5 * 2.5) + ((3 - (1.5 + 0.5)) * 2.5)
MsgBox("Wall area is:" & sngWallArea & " square metres")
'(2) calculate area ofone rollof wallpaper
sngOneRollArea = 0.7 * 10
MsgBox("Area of one roll is:" & sngOneRollArea & " square metres")
'(3) calculate number ofwhole rolls ofwallpaper needed
intNoOfRolls = (sngWallArea sngOneRollArea)+ 1
MsgBox("Noof rollsneededis:" & intNoOfRolls)
'(4)(a) calculate fractionarea ofroll left over
sngRemainderAreaOfRoll = sngWallArea ModsngOneRollArea
MsgBox("Area of roll left over is:" & sngRemainderAreaOfRoll & " sq m")
'(4)(b) calculate length ofroll left over
sngRemainderLengthOfRoll= sngRemainderAreaOfRoll / 0.7
MsgBox("Length ofroll left over is:" & sngRemainderLengthOfRoll & " m")
'(5) calculate total cost ofwallpaper
decCostOfWallpaperPurchased= intNoOfRolls * 8.0
MsgBox("Cost ofwallpaper purchased:£" & decCostOfWallpaperPurchased)
'(6) calculate relative cost ofwallpaper wasted
decCostOfWallpaperWasted = sngRemainderLengthOfRoll* 8.0 / 10
MsgBox("Relative cost ofwallpaper wasted:£" & decCostOfWallpaperWasted)
End Sub
Solution to Exercises 4.2

Part 5 - Making selections using If..Then..Else
Program Control – making selections using “If..Then..Else”
So far we have only written code for a sequence of actions for any one event.
However, in many programs we need to make selections according to certain criteria.
In other words, make a decision.
For example, imagine we were shopping for a new mobile phone, and we could spend
up to £100. In our minds we would be performing the following test as we browsed
the shops looking at all the different phones on offer:
If the phone costs up to £100, then
Ask the shop assistant for more details about the phone
Else
Look for a different phone
End of decision
We could write this process into Visual Basic code. If the cost of the mobile phone
was stored in a variable called decCost, we could write:
If decCost < 101 Then
txtMessage.Text = "Make further enquiries"
Else
txtMessage.Text = "Look for a different phone"
End If
The general way this code structure works is:
If a certain condition is true Then
Do this action
Else
Do this other action
End If
The code written between “If” and “Then” is a condition. A condition is an
expression which may be considered to be either “True” or “False”. If the condition
is “True” then the code up to “Else” is carried out. If the Condition is false, then
the code between “Else” and “End If” is carried out.

Notice that if the condition is False (that is, if the mobile phone does not cost up
to £100), we don’t have to test the condition again. If the phone does not cost up
to £100, then logically it must cost more than £100, and the code underneath the
“Else” will run. Also, the Else is optional. Sometimes, depending on our program,
we don’t need to write any code dealing with an Else condition.
< less than
> greater than
= equal to
<> not equal to
>= greater than or equal to
<= less than or equal to
In our code have used the “ < “ symbol
which means “less than”. This is known as
a relational operator, because it compares
one value with another. The full list of
relational operators is:

Going back to our example of buying a mobile phone, let’s suppose we wanted to
avoid buying very cheap phones because they wouldn’t have all the features we are
looking for. Suppose we didn’t want to look at any phones which cost less than
£50.
We could amend our code as follows:
If decCost > 50 And decCost < 101 Then
Else
End If
The And is known as a logical operator. The full list of logical operators is as follows:
Finally, it is important to realise that in our programs we may be making decisions
which have more than 2 outcomes. In the mobile phone example, we are either
doing one thing or another. We are:
either making further enquiries
or looking for a different phone
But often there will be more than 2 possible courses of action. Suppose we would
consider placing a deposit on the phone if it was outside our price range but had an
internet facility. (Perhaps we would save up and pay for the phone next month.)
Our decision process would look like this:
If the phone costs between £50 and £100, then
Ask the shop assistant for more details about the phone
ElseIf the phone has an internet facility, then
Place a deposit
Else
Look for a different phone
End of decision
And This means both conditions must be True for the entire condition to be True
Or This means if one or both conditions are True, the entire condition is True
Not This reverses the condition so that a True condition will evaluate False, and vice versa.

The code for the above process could be written as follows. (The answer to whether
the phone has an “internet facility” is stored in a “Yes/No” variable called
“blnInternet”):
If decCost > 50 And decCost < 101 Then
ElseIf blnInternetFacility = True Then
txtMessage.Text = "Place a deposit"
Else
End If
We can write as many ElseIf tests as we want to, and each one can result in a
different course of action.
Tax Calculator Program - Scenario
Read the scenario below and then try to carry out the exercises on the following
pages.
Part (a)
A wages department wants you to create a program to help them calculate their
employees’ pay.
At the moment this calculation is done on a hand-held calculator. They want the
program to run as follows:
(1)The wages clerk will type in the Gross Pay and the Tax Allowance for an
employee. (The clerk does not need to type in the employee’s name, just the
figures.)
(2) When the clerk clicks the “Calculate” button, the program will display the Tax
Payable and the Net Pay.
(3) The clerk will then write down the Net Pay for the employee and then type
in figures for the next employee.
The Rate of Tax is 25%. The Tax Payable is calculated by the following equation:
Tax Payable = (Gross Pay – Tax Allowance) x Rate of Tax
Exercises 5.1 – 5.3

Because the wages need to be calculated quickly, the wages clerk does not want to
have to use the mouse on the computer. So the program must run by using only
the computer keyboard. You will therefore need to think about:
- how to get the cursor to move about the screen in the right order, and
- how to clear any text boxes after the wages clerk has processed the figures for
one employee and wants to enter details for the next employee.
Part (b)
Once you have demonstrated that the program works to their satisfaction, the wages
department want you to amend the program so that the wages clerk only has to use
the numeric keypad on the keyboard.
Part (c)
Finally, the wages department will want you to restrict access to the program by
creating a password system. When the program first opens there should be a
Password Form which invites the wages clerk to enter a password into a text box.
If the correct password is entered, the Tax Allowance Calculator form you created in
Parts (a) and (b) should open.
If an incorrect password is entered, the program should display a message stating
that the password is incorrect, the text box on the password form should clear and
the cursor return to the text box. If an incorrect password is entered for a total
of 3 times, a message should be displayed that the program is shutting down, and
the program should terminate.

If…Then…Else - Exercise 5.1 - Tax Calculator
In this exercise we will be looking at the following topics:
 making selections using If…Then…Else statements
 relational operators such as “>” (“greater than”)
 declaring constants
 drawing Group boxes
 using data-type conversion function to convert String data to decimal
Create a new project and draw group boxes, labels, text boxes and buttons on the
form as shown below:
The aim of the program is that the user should be able enter values into
txtGrossPay and txtTaxAllowance. When the Calculate button is clicked, the program
should calculate and display the Tax Payable and Net Pay.
For this exercise we are assuming the Tax Rate is 25%. The Tax Payable is therefore
calculated by subtracting the Tax Allowance from the Gross Pay, and then finding
25% of the remainder.
txtGrossPay
txtTaxAllowance
txtTaxPayable
txtNetPay
grpInput
grpOutput
btnCalculate
Exercise 5.1

For example, if the Gross Pay is £200 and the Tax Allowance (the amount of wage
which is free of tax) is £100, the Tax Payable would be £25 and the Net Pay would
be £175.

First, we need to declare 4 variables in which to store the input data (Gross Pay
and Tax Allowance) and the output data (Tax Payable and Net Pay). The data-
type Decimal is the best one to use for currency data. In the code window, declare
the following variables as Decimal by writing:
Note that when we declare variables in this place (just
below the line Public Class Form1) they are available for
use in any procedure in the form (e.g. code written
behind any button). Because the form is technically
known as a module, variables declared here are known as
module-level variables.
Since the Tax Rate is going to remain constant throughout our calculations, we can
declare it as a constant. (A constant is similar to a variable, except that its value
does not change during the life of the program.) We usually write the names of
constants in CAPITAL letters, separated by an underscore if there is more than one
word. Because Tax Rate is a decimal number it is best to store it in a variable of
data-type: Single. We would therefore name the constant SNG_TAX_RATE and
declare it follows:
Note that when we declare constants we must assign a value to them in the same
line of code. Writing 0.25 is the same as writing 25% or 25/100. Remember, we
cannot write 25% in VB code.
Public ClassForm1
Dim decGrossPay As Decimal 'declare variables
Dim decTaxAllowance As Decimal
Dim decTaxPayable As Decimal
Dim decNetPay As Decimal
Const SNG_TAX_RATE As Single = 0.25 'declare constant
Point
to note

Next we need to write code into btnCalculate which carries out the following steps:
Input Gross Pay and Tax Allowance data from text boxes and store into 2 variables
Calculate Tax Payable as follows:
If Gross Payis greater thanTax Allowance Then
Tax Payable = (Gross Pay – Tax Allowance)x Tax Rate whichis 25%
Else Tax Payable = 0
Calculate Net Pay as follows:
Net Pay= Gross Pay– Tax Payable
Output Tax Payable by displaying in text box txtTaxPayable
Output Net Pay by displaying in text box txtNetPay
The “>” symbol means “greater than”, and it is one of the many relational operators
we can use to compare values in the If…Then…Else statements. The full list of
relational operators is as follows:
< less than
> greater than
= equal to
<> not equal to
Note: the code for calculating the Tax Payable is as follows:
If decGrossPay > decTaxAllowance Then
decTaxPayable= (decGrossPay - decTaxAllowance) * SNG_TAX_RATE
Else
decTaxPayable= 0
End If

Try to work out the rest of the code for btnCalculate yourself. Remember that
when data is written in textboxes it is String data-type by default. We therefore
need to convert this to Decimal data-type when it is input to the two variables
using the CDec( ) function.

If…Then…Else - Exercise 5.2 Tax Calculator Enhancements
In this exercise we will be looking at the following topics which will protect the data
to processed and make our program more user friendly:
 Setting the TabIndex property
 Using the .Focus() method to move focus to a textbox or button
 Enabling / disabling textboxes using .Enabled = True / False
 Formatting output textboxes by using Format(... ,"Currency") function
 Re-formatting input textboxes by using this same function
 Using the .Clear() method to clear a textbox
 Using the _LostFocus(...) event to run code
(a) Using the TabIndex property
We want to make the program user friendly by arranging it to work without the
user having to use the mouse. We can arrange that the Tab key on the keyboard
will move the focus from one control to another in any order we choose. We do
this by setting the TabIndex property of the controls at design time.
Set the TabIndex of the following controls and check the results when running your
program:
Control name TabIndex Result
value
txtGrossPay 1 Puts cursor in text box when form loads
txtTaxAllowance 2 Puts cursor in text box after pressing Tab key
btnCalculate 3 Sets focus to command button after pressing
Tab key so that user only needs to press
Enter key to “Click” the command button
(b) Providing a “Clear” button and improving navigation
We want to make it easier for the user to re-set the form after they have
performed one calculation. Draw another button on the form, set its Text property
to “Clear” and name it btnClear. Double-click it and write the following code in its
Click event procedure:
PrivateSub btnClear_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnClear.Click
txtGrossPay.Clear() 'clear textbox entries
txtTaxAllowance.Clear()
Exercise 5.2

Run your program, enter some data in the first two textboxes and check that both
buttons work as expected.
(c) Protecting data and improving navigation
There is an easy way to provide guidance to the user about which controls to use,
and that is by disabling controls in a set order in response to the user’s actions.
This technique can also be used to protect data.
Double-click on the form itself and write the following code in the Form_Load()
event procedure:
Can you think of similar code you need to write in the btnCalculate_Click() and
btnClear_Click() event procedures?
PrivateSub Form1_Load(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles MyBase.Load
txtTaxPayable.Enabled = False 'disabletextboxes
txtNetPay.Enabled = False
End Sub

If…Then…Else – Exercise 5.3 Tax Calculator – adding a password form
In this exercise we will be looking at the following topics:
 Making further selections using If…Then…ElseIf…Else statements
 Incrementing counter variables using the += operator
 Using .Show() and .Hide() methods with forms
 Using .Clear() and .Focus() methods with controls
We are going to enhance the program we created earlier to incorporate a password
protection system. When the program first opens there should be a Password Form
which invites the user to enter a password into a text box.
Feature A: If the correct password is entered, the Tax Calculator form we created
in Exercise 5.1 should open. If an incorrect password is entered, the program should
display a message stating that the password is incorrect, the text box on the
password form should clear and the cursor return to the text box.
Feature B: If an incorrect password is entered for a total of 3 times, a message
should be displayed that the program is shutting down, and the program execution
should terminate.
Task 1
Add a new form to your project by
Clicking Project / Add Windows Form…
on the top menu of the design window.
Accept the name of the new form as Form2
Resize the form so that it resembles
the size of a logon screen and draw
the controls as illustrated:
To create Feature A described above, add the following code to the OK button’s
Click() event. Run your program and check if it works as expected by entering an
incorrect password and clicking “OK”, then the correct password (“tax”) and clicking
“OK”.
Private SubbtnOK_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnOK.Click
'if password correct
If txtPassword.Text = "tax" Then
'display message
MsgBox("Access to Tax Calculator permitted.")
'show Tax Calculator form
txtPassword
btnOK
Exercise 5.3

Task 2
To create Feature B we need to amend the code we have just written so that if an
incorrect password is entered for a total of 3 times, a message should be displayed
that the program is shutting down, and the program execution should terminate.
We need to create a variable which will keep a tally of the number of times the OK
button has been clicked, then add an ElseIf statement to our If…Then…Else
construction to add further conditions to the decision-making process. Add/amend
the following code shown in bold and highlighted below.
(Note: Be careful to declare the variable intAttemptNumber outside the
btnOK_Click() procedure. If you declare it inside the procedure, it won’t hold its
value between button clicks and won’t count up the number of incorrect password
attempts.)
Public ClassForm2
Dim intAttemptNumber As Integer
Private SubbtnOK_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnOK.Click
'increment counter to store number of attempts
intAttemptNumber += 1
'if passwordcorrect
If txtPassword.Text = "tax" Then
'displaymessage
MsgBox("Access to Tax Calculator permitted.")
'showTax Calculator form
Form1.Show()
'and hide Passwordform
Me.Hide()
'else if attempt number lessthan3
ElseIf intAttemptNumber < 3 Then
'displaymessage
MsgBox("Password incorrect. Please re-type password.")
'clear text box
txtPassword.Clear()
'and put cursor back in text box
txtPassword.Focus()
Else
'else display message

Further study
Can you think how to incorporate the number of incorrect attempts into the message
displayed to the user, like this:

Public Class Form1
Dim decGrossPay As Decimal 'declare variables
Dim decTaxAllowance As Decimal
Dim decTaxPayable As Decimal
Dim decNetPay As Decimal
Const SNG_TAX_RATE As Single = 0.25 'declare constant
'---------------------------------------------------------------------
Private Sub btnCalculate_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnCalculate.Click
'(1) INPUT from textboxes into variables:
'****************************************
decGrossPay = CDec(txtGrossPay.Text) 'store Gross Pay
decTaxAllowance = CDec(txtTaxAllowance.Text) 'store Tax Allowance
'(2) CALCULATE using only variables:
'***********************************
'(a) calculate Gross Pay
If decGrossPay > decTaxAllowance Then 'if Gross Pay > Tax Allowance
decTaxPayable = _
(decGrossPay - decTaxAllowance) * SNG_TAX_RATE 'calculate Tax Payable
Else
decTaxPayable = 0 'else Tax Payable = 0
End If
'(b) calculate Net Pay
decNetPay = decGrossPay - decTaxPayable 'calculate Net Pay
'(3) OUTPUT from variables to textboxes
'**************************************
txtTaxPayable.Text = decTaxPayable 'output Tax Payables
txtNetPay.Text = decNetPay 'output Net Pay
End Sub
'---------------------------------------------------------------------
End Class
Solution to Exercise 5.1

Part 6 - More on making selections using If..Then..Else
Sports Club Membership Fees Program - Scenario
Part (a) – creation of basic program
A newly-opened local sports club wants has ask you to create a program to help
them display the difference subscription fees payable by new members.
There are 3 rates:
 Full rate (“F”) is £100
 Senior rate (“S”) is £75
 Junior rate (“J”) is £50
The club wants you to create a program to be used by the receptionist, to run as
follows. The receptionist will enter one letter (either “F”, “S” or “J”) and the
program will display a fee of either £100, £75 or £50 respectively.
Part (b) enhancing basic program to provide a password protection form
The Sports Club want you to restrict access to the program by creating a password
system. When the program first opens there should be a Password Form which
invites the user to enter a password into a text box If the correct password is
entered, the Membership Fees form you created in Part (a) should open.
If an incorrect password is entered, the program should display a message stating
that the password is incorrect, the text box on the password form should clear and
the cursor return to the text box. If an incorrect password is entered for a total
of 3 times, a message should be displayed that the program is shutting down, and
the program should terminate.
Part (c) enhancing basic program to provide a printed receipt
The Sports Club also want the program to provide a printed receipt for each
member. The receipt show contains the following data:
 member name
 member type
 fee paid
 date
Exercise 6.1

Part (d) enhancing basic program to work without a mouse
Once you have demonstrated that the program works to their satisfaction, the
sports club wants you to amend the program so that the receptionist only has to
use the keyboard to perform most of the repetitive operations. You will therefore
need to think about:
 how to get the cursor to move about the screen in the right order, and
 how to clear any text boxes after the receptionist has processed the details
for each member.
If..Then..Else – Exercise 6.1 Using multiple criteria to make selections
We can use an If… Then… ElseIf statement in the Click Event for
btnCalculateFeeIfThenElse, (highlighted below):
Private Sub btnCalculateFeeIfThenElse_Click(...)
Dim strMemberType As String 'declare variables
Dim decFee As Decimal
'INPUT data
strMemberType = txtMemberType.Text 'load data into variable
'CALCULATE Membership Fee
If strMemberType = "F" Then 'if Member Type is "F"
decFee = 100 '.. load 100 into variable
ElseIf Then 'if Member Type is "S"
'.. load 75 into variable
ElseIf Then 'if Member Type is "J"
'.. load 50 into variable
Else 'if Member Type is none of the above,
MsgBox("YouNeedto input F, S or J in UpperCase") '..display message
End If
'OUTPUT data
txtDisplayFee.Text = FormatCurrency(decFee, 2) 'format output to currency
'..& display into text box
btnCalculateFeeIfThenElse
txtMemberType
txtDisplayFee
Exercise 6.1 continued
Create the Sports Club Membership Fees form shown
here. In this exercise, the fee for a Full member is
£100, that for a Senior is £75 and that for Junior
is £50.

End Sub
See if you can complete the missing code listed above, copy all the code into your
program and then check the program runs as expected.
Further study
In the above example, if the user types in a lowercase letter “f”, “s” or “j”, these
letters are not recognised. See if you can amend your code so that the user can
type in either uppercase or lowercase “F”, “f”, “S”, “s”, “J” or “j”.
(HINT: you can use the Or operator to add criteria to each If / ElseIf statement.
If..Then..Else – Exercise 6.1 SOLUTION
'INPUT data
strMemberType = txtMemberType.Text 'loaddata into variable
If strMemberType = "F" OrstrMemberType = "f" Then 'if MemberType is "F" or "f"
ElseIf strMemberType = "S" OrstrMemberType = "s" Then'if MemberType is "S" or "s"
ElseIf strMemberType = "J" OrstrMemberType = "j" Then'if MemberType is "J" or "j"
MsgBox("YouNeed to input F, f, S, s, J or j") '..display message
End If
'OUTPUT data
txtDisplayFee.Text = FormatCurrency(decFee, 2) 'format output to currency
'.. & display into text box
End Sub
Exercise 6.1 continued

Part 7 Creating menus using the MenuStrip Control
MenuStrip Control
Exercise 7.1 adding a menu to the Tax Calculator
Open your Tax Calculator program which you completed in Exercise 5.2
Exercise 7.1
Drag a MenuStrip Control
onto the form. An icon
will appear in the grey
Component Tray below the
form, and a blue menu bar
will appear on the top
part of the form
containing he words “Type
Here”.

Double-click on the word “Exit” on the top-level menu and the following event
procedure should open in the code window. Type in the code Application.Exit() as
shown
Private SubExitToolStripMenuItem_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles ExitToolStripMenuItem.Click
'exit program
Application.Exit()
End Sub
Run your program and check that when you click the menu items File / Exit with
your mouse, the program exits.
Further study
Add a second top-level menu
item “Options”. Add two sub-
menu items beneath this:
“Calculate” and “Clear”:
Double-click on the “Calculate” menu item and write the following code in the event
procedure:
Private SubCalculateToolStripMenuItem_Click(ByValsender As System.Object, _
ByVal e As System.EventArgs) Handles CalculateToolStripMenuItem.Click
'click Calculate button remotely(evoke PerformClickmethod)
btnCalculate.PerformClick()
End Sub

Run your program and see if the Calculate menu item performs the calculation in the
same way as when you click the Calculate button.
See if you can work out how to add code to the Clear menu item to clear all the
textboxes and place the cursor back in the Gross Pay textbox.
Can you think of any other menu items and sub-menus you may want to add to
enhance your program?

Part 8 Making selections using Select Case
Select Case
Exercise 8.1 Demonstration of advantage of Select Case construction
Complete the following code (and include a message which responds to the user
entering any number not between 1 and 12):
Private Sub btnMonth_Click(...) Handles btnMonth.Click
Dim intMonthNumber As Integer
'input month number intovariable
intMonthNumber = CInt(txtNumber.Text)
'output monthbasedonmonth number
Select Case intMonthNumber
Case 1
MsgBox("Youhave selectedJanuary")
Case 2
MsgBox("Youhave selectedFebruary")
'** continue coding from this point onwards **
End select
End Sub
txtNumber
btnMonth
Exercise 8.1

Sports Club Membership Fees Program - Revisit of scenario:
converting If..Then..Else to Select Case
Select Case – Exercise 8.2 Membership fees program revisited
We have looked at two program control structures so far:
(1) A straight sequence of commands, which are executed one after the other.
(2) A selection using “If ... Then... ElseIf… Else… End If”
There is an alternative to the If statement, which is the Select Case structure.
We have already used an If… Then… ElseIf statement in the Click Event for
btnCalculateFeeIfThenElse, (highlighted below):
'INPUT data
strMemberType = txtMemberType.Text 'loaddata into variable
If strMemberType = "F" Then 'if Member Type is "F"
ElseIf strMemberType = "S" Then 'if Member Type is "S"
ElseIf strMemberType = "J" Then 'if Member Type is "J"
MsgBox("YouNeedto input F, S or J in UpperCase") '..display message
btnCalculateFeeIfThenElse
txtMemberType
txtDisplayFee
btnCalculateFeeSelectCase
Exercise 8.2
Existing code
Open (or create) the Sports Club Membership
Fees form shown here. In this exercise, the
fee for a Full member is £100, that for a
Senior is £75 and that for Junior is £50.
Run your program and check that the first
button works as expected before coding the
second button (see next page).

End If
'OUTPUT data
txtDisplayFee.Text = FormatCurrency(decFee, 2) 'format output to currency & display into text box
End Sub
Using the Select Case structure as an alternative to the If…Then…Else structure.
Code the btnCalculateFeeSelectCase button as follows and check the program runs
with this alternative code. Compare the two constructions.
Select Case strMemberType
Case "F" 'if Member Type is "F"
decFee = 100 '..load 100 into variable
Case "S" 'if Member Type is "S"
Case "J" 'if Member Type is "J"
Case Else 'if Member Type is none of the above,
MsgBox("You Needto input F, S or J in UpperCase") 'display message
End Select
Each Case acts like an If / ElseIf Statement. The instructions after an individual
Case are carried out if the variable being tested matches it.
Further study:
Multiple tests within one “case” using a comma to separate tests.
In the above example, if the user types in a lower case letter “f”, “s” or “j”, these
letters are not recognised. We can get round this by the following construction:
Select Case strMemberType
Case "F", "f" 'if Member Type is "F"or "f"
decFee = 100 '..load 100 into variable
Case "S", "s" 'if Member Type is "S" or "s"
Case "J", "j" 'if Member Type is "J" or "j"
Case Else 'if Member Type is none of the above, display message
MsgBox("You Needto input F, S or J in Upper or LowerCase")
End Select
Try amending your code and check if it works.

Select Case - Further theory
Testing for a range using the “To” keyword.
You may wish to display exam grades according to a range of marks obtained by
students. You would use the keyword “To” and the code would look something
like this:
Select Case txtExamGrade.Text
Case 90 To 100
strGrade = “A”
Case 60 To 89
strGrade = “B”
Case 40 To 59
strGrade = “C”
Case 0 To 39
strGrade = “FAIL”
Case Else
MsgBox ("You Need to input a number between 0 and 100")
End Select
Using “Case Is” followed
by “relational operators”
You can also test how the input value compares to another value by using the
optional keyword “Is" followed by a relational operator in this way:
Select Case decSales
Case Is > 2000
decCommission = (decSales * 10 / 100) + 100
Case Is > 1750
decCommission = (decSales * 10 / 100)
Case Is > 1000
Case Is > 750
Case Is > 500
< less than
> greater than
= equal to
<> not equal to

Case Else
decCommission = 0
End Select

Select Case Demonstration of advantage of If..Then..Else
construction over Select Case construction
Private Sub btnOK_Click(...)HandlesbtnOk.Click
Dim intAge As Integer
Dim strGender As String
'input age and gender
strGender = CStr(txtInputGender.Text)
intAge = CInt(txtInputAge.Text)
'process data and displayappropriate message
If strGender = "M" And intAge < 21 Then
MsgBox("Premium is £500")
ElseIf strGender = "M" And intAge >= 21 Then
ElseIf strGender = "F" And intAge < 21 Then
ElseIf strGender = "F" And intAge >= 21 Then
Else
MsgBox("Youhave entered invaliddata")
End If
End Sub We cannot test 2 conditions at once
using Select Case

Select Case – Exercise 8.1 SOLUTION
Solution to Exercise 8.1
Private Sub btnMonth_Click(...) Handles btnMonth.Click
Dim intMonthNumber As Integer
'input month number intovariable
intMonthNumber = CInt(txtNumber.Text)
'output monthbasedonmonth number
Select Case intMonthNumber
Case 1
MsgBox("Youhave selectedJanuary")
Case 2
MsgBox("Youhave selectedFebruary")
Case 3
MsgBox("Youhave selectedMarch")
Case 4
MsgBox("Youhave selectedApril")
Case 5
MsgBox("Youhave selectedMay")
Case 6
MsgBox("Youhave selectedJune")
Case 7
MsgBox("Youhave selectedJuly")
Case 8
MsgBox("Youhave selectedAugust")
Case 9
MsgBox("Youhave selectedSeptember")
Case 10
MsgBox("Youhave selectedOctober")
Case 11
MsgBox("Youhave selectedNovember")
Case 12
MsgBox("Youhave selectedDecember")
Case Else
MsgBox("Youhave not entereda number between1 and12")
End Select
'clear textbox
txtNumber.Clear()
'put cursor backintextbox
txtNumber.Focus()
End Sub

Part 9 - Iterations (loops) using For..Next
For…Next loops - underpinning knowledge
Background
There are 3 program control structures covered by this course. We have already
looked at the first two:
- sequences (one instruction after another)
- selections (such as “If… Then… Else” or “Select Case” statements)
The third program control structure introduces the concept of iteration (meaning
“repeat the process”) using loops. There are two types of loop:
the counter loop, and
the conditional loop (such as “Do… While” ).
Here we are only going to deal with the counter loop (otherwise known as the “For…
Next” loop).
Example
Suppose we wanted to make the computer beep 5 times. (By the way, there is a
simple line of code which makes the computer beep, namely: “beep”!) You could put
this line of code behind a command button, and press the button 5 times:
Private Sub btnBeep_Click(...)
Beep
End Sub
However, what if we wanted to only click the command button once, and then make
the code run automatically 5 times? The answer is to use a counter loop (known as
a “For…Next” loop). For… Next loops need to have a variable in which to store the
number of times the code should be run. In this example, let us name the variable
“intCounter” and declare it as an integer. The code would be written as follows:
Dim intCounter As Integer
For intCounter = 1 To 5
Beep
Next intCounter
End Sub
This code means:
“Increment the value of the “intCounter” variable from 1 to 5,

and every time you increment it, execute the code below”.
This is the simplest way of using the “For… Next” loop, but you need to know some
more details to use it properly (covered on next handout). For now, try the
exercise overleaf.

For..Next Loops - Exercise 9.1 Beep exercise
Create a form with a button as shown below. We want the code to produce 5
“beeps” when the button is pressed. However, modern computers run so fast that
you will never hear the 5 beeps, so instead we will use a Message Box to produce the
beeps. (Message Boxes require user response, which “interrupts” the execution of
the code so you can see how the code in fact loops 5 times.)
Write the code below into the “Click event” sub-procedure of the button btnBeep:
Dim intCounter As Integer
For intCounter = 1 To 5
MsgBox("Press to beep")
Next intCounter
End Sub
After pressing the “beep” button, you will find that a
MessageBox similar to this one appears, and after
clicking “OK” it will re-appear another 4 times.
Next, it would be good to make the Message Box tell us how many times the code
has looped.
To do this, we can include the name of the counter variable into the MsgBox
function. This will display the contents of the variable each time the code loops.
However, we will need to:
(1)convert the counter variable data from an integer into a string, and then
(2) “tack it on” to the existing message string (known as concatenation)
To convert the variable data into a string we use the conversion function CStr( )
and put the name of the variable into the brackets, i.e. CStr(intCounter). We then
“tack it on” to (concatenate it to) the original message using the “&” symbol:
MsgBox("Press to beep. Iteration no: " & CStr(intCounter))
Alter you code as above and see what effect this has.
Exercise 9.1

(Note: we will be looking in more detail at how to use Message Boxes later in the
course.)

For.. Next Loops - Underpinning knowledge (continued)
Counting in steps
By default, the “For… Next” loop counts upwards in steps of 1, unless you tell it
otherwise.
So, the value of the variable “intCounter” above became: 1, then 2, then 3, then
4, then 5, as the loop was repeated 5 times.
However, you can tell it to count upwards in increments other than 1, by adding
the word “step” to the line of code. You could make the loop count up to 10
in steps of 2, for example:
For intCounter = 1 To 10 Step 2
The result here would be that the loop is repeated 5 times. (The value of the
variable would be 1, 3, 5, 7, and 9.)
Counting backwards
There are times when you will want to count down instead of counting up. You
do this by using a negative “step” number. The example below again will run the
code 5 times.
For intCounter = 5 To 1 Step -1
In summary, the general structure of the “For… Next” loop is shown below.
(the code written in brackets [ ] is optional)
For countervariable = startnumber to endnumber [Step stepnumber]
Next [countervariable]
(3) Using variables for the start and end numbers.
Body of code
to be repeated

“For… Next” loops can become very useful by substituting variables for either the
start or end numbers (or both).
This method is used, for example, when the user puts in a number and you need
to get the code to repeat that same number of times. This is demonstrated in
the following exercise.

For.. Next loops - Exercise 9.2 - Mobile phone credits exercise
If we were crediting a mobile phone with £10 vouchers; rather than enter each value
we might want to be able to enter how many vouchers were being presented. We
could just multiply the two together but that would be too easy and wouldn’t show
the working of the iterative loop.
We will use a form like the one below. The form above should accept the value of
vouchers, their number and then calculate the total credit.
The user should enter the value of the vouchers and the number. When the calculate
button is depressed, a message box should appear and show the number of times a
credit voucher has been entered, as shown below:
When the user clicks “OK” on the message box, it keeps re-appearing until all the
vouchers have been entered. Create a form like the one above and see if you can
work out the code.
Extended Task
txtValue
txtNumber
txtCredit
btnCalculate btnClear
then… etc.
Exercise 9.2

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