Edited Session1

8/2/2019 Edited Session1

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Programming in VB.net / Chapter 1 / 1 of 24

Chapter 1


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Objectives

Identify VB.net as part of .Net framework

Declare variables and constants

Discuss programming constructs

Implement arrays

Discuss OO features of VB.net

Implement typecasting


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Features of VB.net

VB.net is:

A part of Visual Studio.net

A full-fledged object-oriented language

The only language in VS.net that providesbackground compilation

The only language in VS.net that supportslate binding

Not case-sensitive like C, C++, or Java


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Data types in VB.net

Category Data type Length(in bits)

Numeric Integer 32

Long 64

Decimal Decimal 128

Character Byte 8

Char 16


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Data types (Cont)

Category Data type Length(in bits)

String String -

Object Object -


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An Example

Dim d1 As Double

Dim d2 As Object

Dim d3, d4, d5 As IntegerDim mystring As String

Dim a As Integer = 5

d1 = 12

d2 = 10.5

d3 = 4

mystring = Jonathan


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Declaring Constants

Syntax to declare a constant is as follows:

[Public | Private | Friend | Protected |Prot

ected Friend]Constconstantname [As type]= expression

For example:

Public Const DaysInYear = 365

Private Const WorkDays = 250


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Programming Constructs

Decision statements

VB.net provides 3 decision statements:If ..then

If..then..else

Select..Case

If-then-elseIf-then


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An Example(1)

Dim KRA As Decimal

If KRA = 1 Then

Return Bonus * 0.1

ElseIf KRA = 2 Then

Return Bonus * 0.09

ElseIf KRA = 3 Then

Return Bonus * 0.07

ElseReturn 0

End If


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An Example(2)

Dim KRA As Decimal

Select Case KRA

Case 1 ' KRA is 1.

Return Bonus * 0.1

Case 2, 3 ' KRA is 2 or 3.Return Bonus * 0.09

Case 5 To 7 ' KRA is 5, 6, or 7.

Return Bonus * 0.07

Case 4, 8 To 10 ' KRA is 4, 8, 9, or 10.

Return Bonus * 0.05

Case Is < 15 ' KRA is 11, 12, 13, or 14.

Return 100Case Else ' KRA is < 1 or > 14.

Return 0

End Select


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Programming Constructs

Loop structures supported by VB.net are:

While

Do..Loop

For..Next

For Each..Next


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Example for Loops

Dim Cnt As Integer = 0

Dim Nbr As Integer = 10

While Nbr > 6

Nbr = Nbr - 1

Cnt = Cnt + 1

End While

Dim Cnt As Integer =0

Dim Nbr As Integer =10

Do While Nbr > 6

Nbr = Nbr 1

Cnt = Cnt + 1

Loop

While Loop Do..Loop


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Example for Loops -11

Dim Num1,Total AsInteger

For Num1= 1 To 5 Step 1

Total = Total + Num1

Next Num1

Dim X As Integer

For Each X In A

X = 128

Next X

For..Next For Each..Next


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Arrays

Arrays are objects in VB.net.

An array can be of any fundamental datatype, a structure, or an object class.

Array variables can have the Public,

Protected, Friend, Private, or ProtectedFriend specifier.

100

250

640

710Cynthia

Patrick


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Example for Arrays

Dim Expenditure(366) As Decimal

Dim I As Integer

For I = 0 to 365

Expenditure(I) = 20

Next I

Creates

Singledimensionalarray

The above code declares the array variable Expenditure, initializes it tohave 366 elements, and then assigns an initial value of 20 to eachelement.


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Example for arrays - 11

Dim EmpData(3) As Object

EmpData(0) = "astalavista"

EmpData(1) = "42 Heaven Towers"

EmpData(2) = 100

EmpData(3) = Format("09-10-1992", "Date")

Mixing data types in an array is possible if it is declared of typeObject. The following example stores employee information in thearray variable EmployeeData.


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Multidimensional Arrays

Dim Num1, Num2 As IntegerDim MDim0, MDim1 As IntegerDim MatA(10, 10) As Double

MDim0 = MatA.GetLength(0) 1MDim1 = MatA.GetLength(1) - 1

For Num1 = 0 To MDim0For Num2 = 0 To MDim1MatA(Num1, Num2) = (Num1 * 10) + Num2

Next Num2Next Num1

CreatesMulti-dimensionalarray


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Redim Statement

ReDim Preserve MyArray(5, 20)

The above statement allocates a new array, initializes itselements from the corresponding elements of the existing

MyArray, and assigns the new array to MyArray.


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Object-oriented Features

Object-oriented language

Abstraction Polymorphism

Encapsulation Inheritance


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Declaring Classes

A class is declared with the Class..End Class declarations.

An Example:

Public Class TestClass

End Class


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Option Statement Variations

Option statement Value Description

Option Explicit On Requires declaration of all thevariables before they are used

Off Variables can be used withoutdeclaring them (Default)

Option Compare Binary Strings are compared using textalgorithm


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Option Statement Variations-11

Optionstatement

Value Description

Option Strict On Automatic type correction will nottake place

Off Automatic type correction will takeplace (Default)


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Implementing Typecasting

Typecasting in VB.net is implemented by means ofthe Type() statement.

For example:

Dim Num1 As Long

Dim Num2 As Double

Num1 = 500

Num2 = CType(Num1,Double)

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