Visual Basic Fundamental Concepts

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.

Toolbox and Controls

Label control Textbox

control

Button control

Toolbox

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

Creating a New Project

Open Visual Studio 2005

Click Project after

Create:

Choosing Project Language, Template, and Project Name

Select Visual Basic

– Windows Windows

Application Enter Project

Name (Lab1 in example)

Click OK

View StartupForm andSet Properties

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

• 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

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

Average of List of Grades

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

If statement Example with Else part

Syntax with Else– If <Condition> then

<statement_list1>– Else

<statement_list2>– End if

Example :– If hours > 40 then

overtimeHours = hours – 40– Else

overtimeHours = 0– End If