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Integrated Development Enviroment
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.
Basic Controls
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
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 EventForm 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
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
Dim– Dim <variable> as <data-type>
Dim avg as double Dim nmbr as integer Dim flag as boolean
Assignment– <variable> = <expression>
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
Choosing Project Language, Template, and Project Name
Select Visual Basic
– Windows Windows
Application Enter Project
Name (Lab1 in example)
Click OK
Problem Analysis & Application Development
Analyze Problem– Example :
Find averages of pairs of numbers, number1 and number2
– Input : number1, number2– Process : average = (number1 + number2) / 2– Output : average
Project Implementation & Software Development
Design Solution– Choose forms and controls
Select label – textbox pairs for – Input : number1 and number2 and – Output : average
Select buttons to launch processes– Average
Write code to implement process 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
• 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
TypeValues Statement
TypeSyntax
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
Controls and Associated Events
Control EventForm 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
Analyze Problem– Example :
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
If statement for Control
If statement performs an action (<statement_list>) if a condition (<condition>) is true.
Syntax :– If <Condition> then
<statement_list>
– End if