vb concepts

8/13/2019 Vb Concepts

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Visual Basic FundamentalConcepts


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Integrated Development Enviroment

Generates startup form for new project on which toplace controls.

Features toolbox from which controls can beselected & placed on form.

Features intellisense which prompts for completionof statement or object reference.

Provides immediate syntax checking.

Provides online debugging, displaying intermediatevalues.

Provides HELP feature.


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Toolbox and Controls

Labelcontrol Textbox

control

Button

control

Toolbox


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Basic Controls

Label : Displays information through its Textproperty.

Textbox : Information Entry, Display, andTransfer through its Text Property. Usename of textbox to access information orrespond to Gotfocus event.

Button : Information Display through its TextProperty. Use name of button to respondwith subroutine to its Click event.


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Event Driven Programming

Before event driven programs, typical

applications were executed by the computerunder control of the application.

With event driven programs, the operating

system detects user interactions (mouse

click, tab key, etc.), passes them to theapplication, and a control responds by

running a subprogram.


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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 usertabs out of box


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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


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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 areassigned


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Syntax of Dim and Assignment

Statements

Dim Dim as

Dim avg as double

Dim nmbr as integer

Dim flag as boolean

Assignment =

avg = (nmbr1 + nmbr2) / 2

flag = false


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Variables and Assignment Statements

Dim message As String declares string variable

'Assign string constant to messages 1 and 2Assignment statement : =

message = "Enter numbers to be & _averaged in 1st and 2nd textboxes

lblStep1.Text = messagemessage = "Click Average button"

lblStep2.Text = message


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Creating a New Project

Open Visual Studio

2005

Click Project after

Create:


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Choosing Project Language,

Template, and Project Name

Select Visual

Basic

Windows Windows

Application

Enter Project

Name (Lab1 in

example) Click OK


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ViewStartupForm and

SetProperties


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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


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Project Implementation & Software

Development

Design Solution Choose forms and controls

Select labeltextbox 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


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Select Label Control

from Toolbox

Click on Form to

position Labeldrag if

desired.

Click on Textbox

Control from Toolbox

Click on Form to

position Textbox to right

of Label


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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 labeltextbox

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

eventdouble click on button

to generate subroutine shell

Labeltextbox pair

Copy with Ctrl-C


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Controls after selection

Now set text properties

of labels and the button

Name textbox and

button controls

Write code for button

click eventdouble click

on button to generate

subroutine shell


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Controls after setting

text properties of labelsand 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


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Write code for button click

event by double clickingbutton

Button code performs

following:

Computes average

Displays average

Clears input boxes

and selects first box


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Test Program in debugger

by switching back to designview

Click debugger button


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Copy Screen to Copy

Buffer by doing a PrintScreen

Paste onto a Word

Document

Type your name & turn in.


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Data types and Statement Types

Data

Type

Values Statement

Type

Syntax

Integer 3, 211, -42, . Declaration Dim as

Double 3.17, 1.414 Assignment =

String Hello, Bob Selection If then

End if

Boolean True, False Repetition For = to

Next


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Controls and Associated Events

Control Event

Form Load event occurs when form is loaded into computermemory

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


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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


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Average of List of Grades


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If statement for Control

If statement performs an action

() if a condition ()

is true.

Syntax :

If then

End if


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If statement Example with Else part

Syntax with Else If then

Else

End if

Example : If hours > 40 then

overtimeHours = hours40

Else overtimeHours = 0

End If

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