Visual Basic Fundamental
Concepts
Integrated Development Enviroment
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Generates startup form for new project on which to
place controls.
Features toolbox from which controls can be
selected & placed on form.
Features intellisense which prompts for completion
of statement or object reference.
Provides immediate syntax checking.
Provides online debugging, displaying intermediate
values.
Provides HELP feature.
Toolbox and Controls
Toolbox
Label
control
Textbox
control
Button
control
Basic Controls
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Label : Displays information through its Text
property.
Textbox : Information Entry, Display, and
Transfer through its Text Property. Use name
of textbox to access information or respond
to Gotfocus event.
Button : Information Display through its Text
Property. Use name of button to respond
with subroutine to its Click event.
Event Driven Programming
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Before event driven programs, typical
applications were executed by the computer
under control of the application.
With event driven programs, the operating
system detects user interactions (mouse
click, tab key, etc.), passes them to the
application, and a control responds by
running a subprogram.
Controls and Associated Events
Control
Event
Form
Load event occurs when form is
loaded into computer memory
Button
Click event occurs when user clicks
button with mouse
Textbox
Lostfocus event occurs when user
tabs out of box
Click event for Avg button
Private Sub cmdAvg_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles cmdAvg.Click
'Compute average and store in text property of tbAvg control
tbAvg.Text = (CInt(tbNum1.Text) + CInt(tbNum2.Text)) / 2
tbNum1.Select()
tbNum1.SelectionStart = 0
tbNum1.SelectionLength = tbNum1.Text.Length
tbNum2.Clear()
lblStep1.Visible = True
lblStep2.Visible = False
End Sub
Variables and Data Types
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Variables are assigned values from a data
type
VB data types include String, Integer,
Double, and Boolean
A Dim statement is used to declare a variable
and the data type from which its values are
assigned
Syntax of Dim and Assignment
Statements
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Dim
–
Dim <variable> as <data-type>
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Dim avg as double
Dim nmbr as integer
Dim flag as boolean
Assignment
–
<variable> = <expression>
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avg = (nmbr1 + nmbr2) / 2
flag = false
Variables and Assignment Statements
Dim message As String ‘declares string variable
'Assign string constant to messages 1 and 2
‘Assignment statement : <variable> = <expression>
message = "Enter numbers to be “ & _
“averaged in 1st and 2nd textboxes“
lblStep1.Text = message
message = "Click Average button"
lblStep2.Text = message
Creating a New Project
Open Visual Studio
2005
Click Project after
Create:
Choosing Project Language,
Template, and Project Name
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Select Visual
Basic
–
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Windows
Windows
Application
Enter Project
Name (Lab1 in
example)
Click OK
View
Startup
Form and
Set
Properties
Problem Analysis & Application
Development
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Analyze Problem
–
Example :
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Find averages of pairs of numbers, number1 and
number2
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Input : number1, number2
– Process : average = (number1 + number2) / 2
– Output : average
Project Implementation & Software
Development
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Design Solution
–
Choose forms and controls
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Select label – textbox pairs for
–
Input : number1 and number2 and
– Output : average
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Select buttons to launch processes
–
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Average
Write code to implement process
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Gets number1 and number2 values
Computes average = (number1 + number2) /2
Displays average
• Select Label Control
from Toolbox
• Click on Form to
position Label – drag if
desired.
• Click on Textbox
Control from Toolbox
• Click on Form to
position Textbox to right
of Label
• Name textbox tbNumber1
• Holding shift key down,
select label and textbox
together
• Copy with Ctrl-C
• Paste with Ctrl-V (for
Number2 entry.
• Select button Control and
position below label – textbox
pair
• Paste again below button
for output.
• Set text properties of labels
and the button
• Name textbox and button
controls
• Write code for button click
event – double click on button
to generate subroutine shell
• Label – textbox pair
• Copy with Ctrl-C
• Controls after selection
• Now set text properties
of labels and the button
• Name textbox and
button controls
• Write code for button
click event – double click
on button to generate
subroutine shell
• Controls after setting
text properties of labels
and the button
• Name textbox and
button controls
• Name of textbox for
output
• Write code for button
click even by double
clicking button
• Button code should
• Compute & display
average
• Clear input boxes
and select first box
• Write code for button click
event by double clicking
button
• Button code performs
following:
• Computes average
• Displays average
• Clears input boxes
and selects first box
• Test Program in debugger
by switching back to design
view
• Click debugger button
• Copy Screen to Copy
Buffer by doing a Print
Screen
• Paste onto a Word
Document
• Type your name & turn in.
Data types and Statement Types
Data
Type
Values
Statement
Type
Integer
3, 211, -42, .
Declaration Dim <variable> as <datatype>
Double
3.17, 1.414
Assignment <variable> = <exp>
String
“Hello”, “Bob”
Selection
If <condition> then
<statement_list>
End if
Boolean
True, False
Repetition
For <variable> = <start> to <end>
<statement_list>
Next
Syntax
Controls and Associated Events
Control
Event
Form
Load event occurs when form is loaded into computer
memory
Button
Click event occurs when user clicks button with mouse
Textbox
Lostfocus event occurs when user tabs out of box
Listbox
SelectedIndexChanged occurs when user clicks a list
item with mouse
Problem Analysis & Application
Development
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Analyze Problem
–
Example :
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Find average of list of numbers incrementally by
–
Keeping track of number of numbers
– Keeping track of sum of numbers
– Computing average after each number
– Displaying numbers in a listbox
Average of List of Grades
If statement for Control
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If statement performs an action
(<statement_list>) if a condition (<condition>)
is true.
Syntax :
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If <Condition> then
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–
<statement_list>
End if
If statement Example with Else part
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Syntax with Else
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If <Condition> then
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Else
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<statement_list1>
<statement_list2>
End if
Example :
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If hours > 40 then
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Else
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overtimeHours = hours – 40
overtimeHours = 0
End If