Tutorial: Programming in Visual Basic 6.0

Tutorial: Programming in Visual Basic 6.0

This tutorial contains a beginner’s guide to Visual Basic 6.0, introducing the programming
environment, defining key terms and introducing exercises to demonstrate the five
control structures (sequence, selection: binary and multiway, iteration: pre and post
test).

Syllabus outcome
H5.3 A student selects and applies appropriate software to facilitate the design and
development of software solutions

Students learn to implement a fully tested and documented software solution in a
methodical manner. (SDD syllabus, p.51)

The following headings may help you navigate:
Activity 1: Welcome screen and menu editor
Activity 2: Event handlers and scroll bars
Naming conventions
Data types, variables and functions
Activity 3: Messages and input boxes
Activity 4: Create a calculator and avoid division by zero
Sequence
Binary Selection
Activity 5: Measurement converter
Multiway selection
Activity 6: Multiway selection
Activity 7: Control arrays
Iterations
Activity 8: Pre-test loops
Activity 9: Post-test loops
Activity 10: Random number generator
Activity 11: Using a counter in a pre-test loop
Activity 12: Nested FOR loops and arrays

Organising your first project

The first step is to create a project template within VB, to organise and store your work.
This will consist of a menu structure with headings that will let you access the many
exercises and examples you complete.
Activity 1
• Open VisualBasic 6.0
• Use the file menu to open a new project with a blank form.
• Use the properties window to set
– Main.frm as the form name.
– My programs as the caption.
– BackColor to White.
– BorderStyle to Fixed Single.
– WindowState to Maximised.
• Find the Menu icon and click on it to select it. Enter the following menu headings:

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Quit
Introduction with indented subheadings of

Example1
Example2


Click OK after each menu caption and name are typed.

• Click on Quit menu heading and enter the following code. This procedure is used to
exit from running the project display and return to the design screens.

Private Sub Quit_Click()
Unload me
End
End Sub
• Use the <F5> function key to run the application to verify that the Menu structure is
correct and that the Quit procedure is free from error.
• Use the File menu to save your work as Main.frm and (your intitials)Project1.vbp
• Use the file menu to open a new blank form (or the properties window)
• Set the following form properties:
form name as Welcome
caption to Example1
BackColor to White
BorderStyle to Fixed Single
WindowState to Maximised
• Click on the Example 1 main menu heading and enter the following code:
Private Sub Example1_Click()
Welcome.Show
End Sub

• Save your work and run <F5> to ensure that it is free of errors.



• Add two labels, an image and a command button to create a welcome screen. To do
this

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Select label icon from the toolbox. Click towards the centre-top of your form and
position and resize your label as required.
With the label selected, use the properties window to
Change the caption to WELCOME TO VISUAL BASIC
Choose a bright back colour
Set the font (Arial, underline, alignment centred, size 24 point, forecolour blue)
Repeat to add the Enjoy label.
Use the image icon on your toolbox to add the image to your form. Use the
properties window of the image to select a picture.
Use the command Button icon to add the button. Change its caption to RETURN.
Then double-click the button and add the following line of code after the
Command1_Click() procedure.
–
Unload Welcome

• Use the file menu to save your work and use <F5> to run the application.

• DON’T FORGET TO SAVE (AND BACK UP TO FLOPPY) ALL YOUR WORK.

Event handlers and scroll bars
Some definitions to learn
• An object is a thing — anything that appears on the screen. An object has a set of
properties. Each property of the object has a value.
e.g. Label.Caption = “Welcome to Visual Basic” where

Label is an object
Caption is a property of label
“Welcome to Visual Basic” is a value of the Caption property.

• Events are things that happen on the screen. Event handlers transfer data to
procedures that complete the task. The results of these procedures are returned
back to other screen objects, e.g. onChange onClick

• A procedure is a group of statements designed to perform a specific task. A
procedure attached to an object, such as a button, is a command used to make
something happen, e.g.

Public Sub Command2_Click()
Text1.Text = “This is a procedure.”
End Sub
Add new form to menu
As each new example and exercise solution is to be added to your project you will need
to: • add a new form
• set the form properties using the properties window
• click on the main menu icon with the main form displayed to show the menu
designer
• add a new menu heading
• click on the menu heading to show the procedure code
• to the procedure code, add the statement
FormXX.Show
where FormXX is the new form name.

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Activity 2
1. Open a new form and change its name to ColourChanger. Place the following objects
on this form.
A heading label2 (Caption = Colour Changer)
3 horizontal scroll bars (Set the max value property of all three to 255)
3 other labels (2red, 3Green, 4Blue)
a command button to quit the form (Caption = Return)
another smal label5 under the button with its visible property set to false.




2. Double click each scroll bar and add the following code to its _onChange() event. Use
cut and paste to make the task easier.

Label1.BackColor = RGB(HScroll1.Value, HScroll2.Value, HScroll3.Value)
Label5.BackColor = RGB(HScroll1.Value, HScroll2.Value, HScroll3.Value)
Label1.ForeColor = RGB(255 - HScroll1.Value, 255 - HScroll2.Value, 255 -
HScroll3.Value)
Label5.ForeColor = RGB(255 - HScroll1.Value, 255 - HScroll2.Value, 255 -
HScroll3.Value)
Label5.Visible = True
Label5.Caption = “WOW!”
Label2.BackColor = RGB(HScroll1.Value, 0, 0)
Label3.BackColor = RGB(0, HScroll2.Value, 0)
Label4.BackColor = RGB)0, 0, HScroll3.Value)
3. Double click the return button and add the following code to its _onClick() event

Unload Me

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4. Use the Project Explorer window to return to your main form and double click
example 2 in your menu to add the appropriate code.

5. Use <F5> function key to test your project. Save and backup.
Naming conventions
Up till now, we have often accepted default names, Text1, Label1, etc. In a big project,
this is not good practice as it makes the code harder to read or maintain. Naming
conventions use a prefix of three lowerCase letters to identify the type of control,
followed by a meaningful name. eg. lblTitle
Prefix Abbreviations for Control names
Prefix
Control
Prefix
Control
cbo
combo box
chk
check box
cmd
command button
dir
directory list box
drv
drive list box
fil
file list box
fil
file list box
fra
frame
frm
form
grd
grid
hsb
horizontal scrollbar
img
image
lbl
label
lin
line
lst
list box
mnu
menu
ole
OLE client
opt
option button
pic
picture box
shp
shape
tmr
timer
txt
text box
vsb
vertical scrollbar



Data types in VB
A variable is a named location that holds data. A variable can only hold one datatype.
A program can have as many variables as you need but before you can use a variable it
must be declared.

You use a DIM statement to declare variables (where DIM stands for dimension). Here is
the format of the DIM statement:

Dim VarName As Datatype

e.g. Dim curCost As Currency, Dim strSurname As String
Datatype Description and Range
Prefix
Boolean One of two values only. e.g. True or False e.g. blnIsOverTime bln
Byte
Positive numeric values without decimals from 0-256 e.g.
byt
bytAge
Currency Data that holds dollar amounts from
cur
-$922,337,203,685,477.5808 to +-
$922,337,203,685,477.5807 e.g. curHourlyPay
Date
Date and time values from Jan 1, 100 to Dec 31, 9999 e.g. dte
dteFirstLesson
Double
Numeric values from –1.79769313486232E+308 to
dbl
+1.79769313486232E+308. Often cal ed double-precision.
e.g. dblMicroMeasurement
Integer
Numeric values with no decimal point or fraction from –
int
32,768 to 32,767 e.g. intCount
Long
Integer values beyond the range of Integer datatype from
lng

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–2,147,483,648 to 2,147,483,647 e.g. lngStarDistance
Object
A special datatype that holds and references objects such as obj
controls or forms. e.g. objSoundClip
Single
Numeric values that range from –3,402823E+38 to
sng
3,402823E+38. Often called single-precision.
sngYearSalesFigures
String
Data that consists of 0 to 65,400 characters of alphanumeric str
data including special characters such as @, ^, ½ e.g.
strFirstName
Variant
Data of any datatype used for control and other values for
vnt or
which the datatype is unknown. e.g. vntControlValue
var

A function is a segment of code that accepts zero, one or more arguments and returns a
single result. Visual Basic includes many built-in functions (intrinsic functions). Some
perform basic mathematical tasks. Others manipulate string data such as converting text
to upperCase or lowerCase letters.

An argument is a value you pass to a function so the function has data to work with.

Function names have parentheses at the end to hold the function arguments. Even if a
function has no arguments, the parenthesis are required.

Two intrinsic functions include message boxes and input boxes.

Activity 3: Message and input boxes
Message and input boxes are intrinsic functions in Visual Basic 6.0 which allow the end
user to interact with the program.

Follow the instructions Add new form to menu at the end of Activity 1 to create a new
form with a menu heading on the main form. Cal this “Message and Input Boxes”
• Make the Form.Caption = “Message and Input Boxes”
• Put a label on the top of the form “Computer Conversation”. Underneath have a
command button with the caption “Talk to me!” Name the command button cmdTalk.
• Double click the command button to add the following code sequence.
Private Sub cmdTalk_Click()
Dim strQuestion As String
‘First you must declare your variables’
Dim intAnswer As Integer
‘Then use the input and message box functions’
strQuestion = InputBox(“Type in your name!”, “Ebeneezer”)
intAnswer = MsgBox(“Hello there” & strQuestion, vbOKCancel, “Chat”)
End Sub
• Add a return button, called cmdBack as you did in the ColourChanger, using the code
Private Sub cmdBack_Click()
Form1.Show
End Sub
• Run your program using <F5>. Don’t forget to save your work.

Here are some handy literals (values that don’t change). You don’t have to learn them
as the help prompt supplies a drop down list as you start to type.

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Buttons in Message Boxes
Named Literal
Value
Description
vbOKOnly
0
Displays the OK button
vbOKCancel
1
Displays the OK button and Cancel buttons
vbAbortRetryIgnore 2
Displays the Abort, Retry and Ignore buttons.
vbYesNoCancel
3
Displays the Yes, No and Cancel buttons.
vbYesNo
4
Displays the Yes and No buttons.
vbRetryCancel
5
Displays the Retry and Cancel buttons.

Icons in Message Boxes
Named literal
Value
Description
vbCritical
16
Displays Critical Message icon
vbQuestion
32
Displays Warning Query icon.
vbExclamation
48
Displays Warning Message icon.
vbInformation
64
Displays Information message icon.
vbSystemModal
4096
Displays a System Modal dialog box. The user must
acknowledge this box before doing anything else.

Remarks are added in code to explain the purpose of a section of code or to add
information for code maintenance. If Rem or ‘ is placed in front of the remark, that line
of code is ignored completely.

Activity 4
Create a calculator that can add, subtract, multiply and divide two numbers given by the
user.
[A possible solution might use two input boxes (txtOne and txtTwo) and a label to display
the answer (lblAnswer).

Declare variables:
dblNo1 As Double
dblNo2 As Double
dblAnswer As Double
intError As Integer

Use Val function to change string from input box to a number, then an assignment
statement to put that value into the variable.

dblNo1 =
Val (txtOne.text)
Repeat for second number.

Use a Format function to ensure answer is rounded off to two decimal places.

lblAnswer.Caption = Format (dblAnswer, “#,##0.00”)
If you are very clever, this might be an option for the user.

Ensure that it is not possible to divide by zero, either by entering nothing or by entering
zero. Use the MsgBox() function to indicate the problem to the user.
If Val (txtTwo.Text) = 0
Then
IntError = MsgBox (“You cannot divide by 0!”, VbOkCancel, “Whoops!)
Else …
End If

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Add a clear command button with the following code to allow the user to do another
calculation.

txtOne.Text = “”
txtTwo.Text = “”
lblAnswer.Caption = “”
txtOne.SetFocus

The SetFocus method returns the cursor to the first input box.

Set properties to pretty it up.
Check that it works. Use integers, very big numbers, very small numbers, negative
numbers, zeros, etc. Is your label big enough for al values? If you set the label’s
autosize property to true it will stretch to fit.

Add a remark (put ‘ at the beginning of the line) at the top of your code which includes
your name and the date.

Connect to a Binary Selection menu heading on the main form.

Sequence algorithms
The programs in Activities 1 — 3 were all constructed from sequence algorithm
constructs. Each line of code followed another with only one possible pathway for each
event. So, for each sub procedure, the algorithm would consist of input, output and a
series of process steps, e.g.

Private Sub cmdClear_Click()
`user input
txtOne.Text = “”
`sequence of processes initializing variables
txtTwo.Text = “”
lblAnswer.Caption = “”
txtOne.SetFocus
End Sub
`output


Binary selection
The next group of programs you will write uses the second algorithm construct —
selection. Selection allows multiple pathways for any event and allows for choices to be
made. Selection constructs can be Binary (two way) or Multiway (multiple choices)

Binary selection uses the If – End If or the If – Else – End If statements. Here
is the syntax in Visual Basic.

If comparison test Then

One or more Visual Basic statements
End If

OR

If comparison test Then

One or more Visual Basic statements
Else

One or more Visual Basic Statements
End If

(You have used binary selection in your calculator to prevent a user dividing by zero.)

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Activity 5

Is your measurement in Inches or Centimetres


Enter the measurement 1
Convert it!
The measurement in centimetres is 2.54 cms.


• Add a new menu heading Selections with two subheadings, Binary Selection and
Multiway Selection.
• Write a program to convert inches to centimetres OR centimetres to inches (using the
conversion 1 inch = 2.54 centimetres).
• Use option buttons (from the toolbox) for the user to indicate whether the conversion
is inches to centimetres or centimetres to inches.
• Use IF statements to determine which formula to use based on which option button is
selected. Option buttons are mutually exclusive, i.e. only one can be selected at a
time.
• Connect to menu heading Binary Selection.
• Run the application to ensure that it is working correctly.
• Use your calculator to verify the results. Try it out with some test data including
very large numbers, very small numbers, zero, negative numbers, 0.000000987654.

Multiway selection
In Activity 5 we looked at an example of binary selection. If the selection involves more
than two alternatives, you can use nested If statements but this becomes complicated
and leads to hard-to-read code. It is better to use Case statements. Here is the syntax
for multiple selection through Case statements.
Select Case Expression

Case value


[One or more VB statements]

Case value


[One or more VB statements]

Case value


[One or more VB statements]

Case Else


[One or more VB statements]
End Select

For example:

Select Case intAge

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Case Is < 6


lblTitle.Caption = “Preschool”

Case 6 To 11


lblTitle.Caption = “Primary School”

Case 12 To 18


lblTitle.Caption = “Secondary School”

Case Else


lblTitle.Caption = “Adult”
End Select

Activity 6
1. The post office has the following charges for parcels based upon different weights.

Weight (gram)
Cost
0 – 50
$1.40
51 – 100
$2.70
101 – 250
$4.00
251 – 500
$7.50

Parcels which are heavier than 500 gms are calculated by weight*0.02

Design a project that allows a user to enter the weight in a text box and calculate the
postage. Use Case statements in your code. Link this as CaseWeights under the
Multiway menu heading in your main form.

2. Use a set of check boxes to al ow a user to choose the noise level by the comments,
then output the probable decibel level based on information in the following table.

Decibel level
Comfort level
140+
Extremely painful
90 – 139
Deafening
60 – 89
Disturbing
30 – 59
Distracting
0 – 29
Relaxing

Again use Case statements and link this to the main form menu under the name
NoiseLevels again connected to the Multiway menu heading.

Activity 7
A control array is a set of multiple controls of the same type with the same name (often
created by using the Copy and Paste command). You may have encountered this already
in adding radio buttons or check boxes to your form. Individual controls within the array
are distinguished by having different Index property values. So, if you created a control
array of option buttons called optChoice, the Click event procedure might look like this:

Private Sub optChoice_Click (Index As Integer)
Select Case optChoice (Index)
Case Index = 0
Label1.Caption = "Monday"
Case Index = 1
Label1.Caption = "Tuesday"
Case Index = 2
Label1.Caption = "Wednesday"
Case Index = 3
Label1.Caption = "Thursday"

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