vb_variables.docx

7/30/2019 VB_Variables.docx

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Visual Basic Variable

Variable: Provide temporary storage of data. the variables are assigned names by the programmer when

they are declared so that they can easily be referenced in other places in the application code.

Data type: Define the type of the data that will be stored on variable

Byte

Integer

Long

Decimal

Double

Char

String

Date

Boolean

Variables Declaration

Variables are declared using the Visual Basic Dim keyword. The syntax for a simple declaration of a

variable is as follows:

DimvariableNameAsvariableType

Note: Dim is the keyword which indicates to Visual Basic that a variable is being declared.

scope of a variable

The scope of a variable relates to where else in the application source code the variable is accessible.

Local variables are recognized only in the procedure in which they are declared. They can be declared

with Dim and Statickeywords.

A module level variable is available to all the procedures in the module. They are declared using

the Publicor the Private or DIM keyword.

Array Variable

An array is a consecutive group of memory locations that all have the same name and the same

type.

To refer to an element in the array, we specify the array name and the array element position

number it is called Index


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Declaration

Dim list(10) as integer declares a 10-element array, indexed 0 to 9

Dim sortList(1 To 10) as integer declares a 10-element array, indexed 1 to 10

List(0)=10

List(1)=2

List(list(1))= List(0) + List(1) after execution List(2)=12

Control Array

Similar to arrays of variables, you can group a set of controls together as an array.

The set of controls that form a control array must be all of the same type (all textboxes,all labels, all option buttons, etc.)

The properties of the controls in the control array can vary

To refer to a member of a control array:

ControlName(Index).Property

Ex:

txtOperator(1).Text = +

Event Procedure of control Array

Consider command button = cmdOperator

Private Sub cmdOperator_Click(Index As Integer)

Where parameter Index refer index of control that is clicked

End Sub

Private Sub txtField_KeyPress(Index As Integer, KeyAscii As Integer)

End Sub


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Control Statement

Control Statements are used to control the flow of program's execution.

1) If...Then..Else selection structure

The If...Then selection structure performs an indicated action

Syntax

If Then

statement1

statement2

End If

If Thenstatements1.1

statements1.2

Else

statements2.1

statements2.2

End If

Eg:

Dim marks as integermarks=45If marks >= 40 Then

Print PassElse

Print FailEnd If

2) Nested If Statement

If < condition 1 > Then

statementsElseIf < condition 2 > Thenstatements

ElseIf < condition 3 > Thenstatements

Else

Statements

End If


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Eg:

Dim marks as integermarks=val(txtMarks.Text)If marks >=70 Then

Print Grade is A

Else If marks >=60 ThenPrint Grade is BElse If marks >=50 Then

Print Grade is CElse If marks >=40 Then

Print Grade is S

ElsePrint Grade is F

End If

3) Select Case Structure

Syntax

Select Case expression

Case value1

Block of one or more VB statementsCase value2

Block of one or more VB Statements

Case value3

..

Case ElseBlock of one or more VB Statements

End Select

Eg:

grade=txtgrade.Text

Select Case gradeCase "A"

result.Caption="High Distinction"Case "A-"

result.Caption="Distinction"Case "B"

result.Caption="Credit"Case "C"

result.Caption="Pass"


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Case Else

result.Caption="Fail"End Select

Loop

1)The For...Next Loop

The For...Next Loop is one of the way to make loops in Visual Basic.

Dim x As IntegerFor x = 1 To 50

Print x

Next x

In order to count the numbers from 1 yo 50 in steps of 2, the following loop can be used

For x = 1 To 50 Step 2Print x

Next x

2)Do While... Loop Statement

The Do While...Loop is used to execute statements until a certain condition is met. The following DoLoop counts from 1 to 100.

Dim number As Integernumber = 1

Do While number


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Graphics Method

The Pset Method

The Pset method draw a dot on the screen

Syntax

Pset (x , y ), color

Eg1:

For x= 0 to 50Pset(x,x)Next x

Eg2:

For x= 0 to 100Pset(x,x) , vbMagentaNext x

Eg3:

Private Sub Form_MouseMove(Button As Integer, Shift As Integer, x As Single, Y As Single)

Pset(x,y)

End sub

Other Method

Line (x1, y1)-(x2, y2), color

Circle (x1, y1), radius, color

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