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VB.NET VB.NET
2About the Tutorial
VB.Net is a simple, modern, object
-
oriented computer programming language developed by
Microsoft to combine the power of .NET Framework and the common language runtime with
the productivity benefits that a
re the hallmark of Visual Basic.
This tutorial will teach you basic VB.Net programming and will also take you through various
advanced concepts related to VB.Net programming language.
Audience
This tutorial has been prepared for the beginners to help them
understand basic VB.Net
programming. After completing this tutorial, you will find yourself at a moderate level of
expertise in VB.Net programming from where you can take yourself to next levels.
Prerequisites
VB.Net programming is very much based on BASIC
and Visual Basic programming languages,
so if you have basic understanding on these programming languages, then it will be a fun for
you to learn VB.Net programming language.
Copyright & Disclaimer
© Copyright 2015 by Tutorials Point (I) Pvt. Ltd.
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e content and graphics published in this e
-
book are the property of Tutorials Point (I)
Pvt.
Ltd. The user of this e
-
book can retain a copy for future reference but commercial use of
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art of the content of
this e
-
book in any manner is also not allowed without written consent of the publisher.We strive to update the contents of our website and tutorials as timely and as precisely as
possible, however, the contents may contain inaccurac
ies or errors. Tutorials Point (I) Pvt.
Ltd. provides no guarantee regarding the accuracy, timeliness or completeness of our website
or its contents including this tutorial. If you discover any errors on our website or in this
tutorial, please notify us at
[email protected] Table of Contents
About the Tutorial
................................
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1
VB.NET
3Audience
................................
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................................
................................
.................
1
Prerequisites
................................
................................
................................
................................
...........
1
Copyright & Disclaimer
................................
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............................
1
Table of Contents
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2
1.
VB.NET
â
OVERVIEW
................................
................................
................................
...........
8
Strong Programming Features VB.Net
................................
................................
................................
.....
8
2.
VB.NET
â
ENVIRONMENT
SETUP
................................
................................
.......................
10
The .Net Framework
................................
................................
................................
.............................
10
Integrated Development Environment (IDE) For VB.Net
................................
................................
.......
11
Writing VB.Net Programs on L
inux or Mac OS
................................
................................
.......................
11
3.
VB.NET
â
PROGRAM STR
UCTURE
................................
................................
......................
12
VB.Net Hello World Example
................................
................................
................................
.................
12
Compile & Execute VB.Net Program
................................
................................
................................
......
13
4.
VB.NET
â
BASIC SYNTA
X
................................
................................
................................
....
15
A Rectangle Class in VB.Net
................................
................................
................................
...................
15
Identifiers
................................
................................
................................
................................
..............
17
VB.Net Keywords
................................
................................
................................
................................
..
17
5.
VB.NET
â
DATA TYPES
................................
................................
................................
........
19
Data Types Available in VB.Net
................................
................................
................................
.............
19
Example
................................
................................
................................
................................
................
21
The Type Conversion Functions in VB.Net
................................
................................
.............................
22
Example
................................
................................
................................
................................
................
24
6.
VB.NET
â
VARIABLES
................................
................................
................................
..........
25
VB.NET
4Variable Declaration in VB.Net
................................
................................
................................
..............
25
Variable Initialization in VB.Net
................................
................................
................................
............
27
Example
................................
................................
................................
................................
................
27
Accepting Values from User
................................
................................
................................
..................
28
Lvalues and Rvalues
................................
................................
................................
..............................
28
7.
VB.NET
â
CONSTANTS A
ND ENUMERATIONS
................................
................................
....
30
Declaring Constants
................................
................................
................................
..............................
30
Example
................................
................................
................................
................................
................
31
Print and Display Constants in VB.Net
................................
................................
................................
...
31
Declaring Enumerations
................................
................................
................................
........................
32
Example
................................
................................
................................
................................
................
33
8.
VB.NET
â
MODIFIERS
................................
................................
................................
.........
35
List of Available Modifiers in VB.Net
................................
................................
................................
.....
35
9.
VB.NET
â
STATEMENTS
................................
................................
................................
......
40
Declaration Statements
................................
................................
................................
.........................
40
Executable Statements
................................
................................
................................
..........................
44
10.
VB.NET
â
DIRECTIVES
................................
................................
................................
.........
45
Compiler Directives in VB.Net
................................
................................
................................
...............
45
11.
VB.NET
â
OPERATORS
................................
................................
................................
........
50
Arithmetic Operators
................................
................................
................................
............................
50
Example
................................
................................
................................
................................
................
51
Comparison Operators
................................
................................
................................
..........................
52
Logical/Bitwise Operators
................................
................................
................................
.....................
54
VB.NET
5Example
................................
................................
................................
................................
................
55
Bit Shift Operators
................................
................................
................................
................................
57
Example
................................
................................
................................
................................
................
59
Assignment Operators
................................
................................
................................
...........................
60
Example
................................
................................
................................
................................
................
61
Miscellaneous Oper
ators
................................
................................
................................
......................
62
Example
................................
................................
................................
................................
................
63
Operators Precedence in VB.Net
................................
................................
................................
...........
64
Example
................................
................................
................................
................................
................
65
12.
VB.NET
â
DECISION MA
KING
................................
................................
.............................
67
If...Then Statement
................................
................................
................................
...............................
68
If...Then...Else Statement
................................
................................
................................
......................
70
The If...Else If...Else Statement
................................
................................
................................
..............
71
Nested If Statements
................................
................................
................................
.............................
73
Select Case State
ment
................................
................................
................................
...........................
74
Nested Select Case Statement
................................
................................
................................
...............
76
13.
VB.NET
â
LOOPS
................................
................................
................................
................
78
Do Loop
................................
................................
................................
................................
.................
79
For...Next Loop
................................
................................
................................
................................
......
82
Each...Next Loop
................................
................................
................................
................................
...
85
While... End While Loop
................................
................................
................................
........................
86
With... End With Statement
................................
................................
................................
..................
88
Nested Loops
................................
................................
................................
................................
........
89
Loop Control Statements
................................
................................
................................
.......................
91
VB.NET
6Exit Statement
................................
................................
................................
................................
......
92
Continue Statement
................................
................................
................................
..............................
94
GoTo Statement
................................
................................
................................
................................
....
95
14.
VB.NET
â
STRINGS
................................
................................
................................
.............
98
Creating a String Objec
................................
................................
................................
..........................
98
Properties of the String Class
................................
................................
................................
................
99
Methods of the String Class
................................
................................
................................
...................
99
Examples
................................
................................
................................
................................
.............
105
15.
VB.NET
â
DATE & TIME
................................
................................
................................
....
108
Properties and Methods of the DateTime Structure
................................
................................
............
109
Creating a DateTime Object
................................
................................
................................
................
112
Getting the Current Date
and Time
................................
................................
................................
.....
113
Formatting Date
................................
................................
................................
................................
..
114
Predefined Date/Time Formats
................................
................................
................................
...........
115
Properties a
nd Methods of the DateAndTime Class
................................
................................
............
117
16.
ARRAYS
................................
................................
................................
............................
121
Creating Arrays in VB.Net
................................
................................
................................
....................
121
Dynamic Arrays
................................
................................
................................
................................
...
122
Multi
-
Dimensional Arrays
................................
................................
................................
...................
124
Jagged Array
................................
................................
................................
................................
........
125
The Arra
y Class
................................
................................
................................
................................
....
126
17.
VB.NET
â
COLLECTIONS
................................
................................
................................
...
131
Various Collection Classes and Their Usage
................................
................................
.........................
131
VB.NET
7ArrayList
................................
................................
................................
................................
..............
132
Hashtable
................................
................................
................................
................................
............
136
SortedList
................................
................................
................................
................................
............
138
Stack
................................
................................
................................
................................
...................
142
Queue
................................
................................
................................
................................
.................
144
BitArray
................................
................................
................................
................................
...............
146
18.
VB.NET
â
FUNCTIONS
................................
................................
................................
......
150
Defining a Function
................................
................................
................................
.............................
150
Example
................................
................................
................................
................................
..............
150
Function Returning a Value
................................
................................
................................
.................
151
Recursive Function
................................
................................
................................
..............................
152
Param Arrays
................................
................................
................................
................................
......
153
Passing Arrays as Function Arguments
................................
................................
................................
153
19.
VB.NET
â
SUB PROCEDU
RES
................................
................................
............................
155
Defining Sub Procedures
................................
................................
................................
.....................
155
Example
................................
................................
................................
................................
..............
155
Pass
ing Parameters by Value
................................
................................
................................
..............
156
Passing Parameters by Reference
................................
................................
................................
........
157
20.
VB.NET
â
CLASSES & O
BJECTS
................................
................................
..........................
159
Class Definition
................................
................................
................................
................................
...
159
Member Functions and Encapsulation
................................
................................
................................
161
Constructors and Destructors
................................
................................
................................
..............
162
Shared Members of a VB.Net Class
................................
................................
................................
.....
165
Inheritance
................................
................................
................................
................................
..........
166
VB.NET
8Base & Derived Classes
................................
................................
................................
........................
166
Base Class Initialization
................................
................................
................................
.......................
168
21.
VB.NET
â
EXCEPTION H
ANDLING
................................
................................
.....................
170
Syntax
................................
................................
................................
................................
.................
170
Exception Classes in .Net Framework
................................
................................
................................
..
171
Handling Exceptions
................................
................................
................................
............................
172
Creating User
-
Defined Exceptions
................................
................................
................................
.......
173
Throwing Objects
................................
................................
................................
................................
174
22.
VB.NET
â
FILE HANDLI
NG
................................
................................
................................
175
Binary Files
................................
................................
................................
................................
..........
182
23.
VB.NET
â
BASIC CONTR
OLS
................................
................................
..............................
192
24.
VB.NET
â
DIALOG BOXE
S
................................
................................
................................
.
285
25.
VB.NET
â
ADVANCED FO
RM
................................
................................
............................
307
26.
VB.NET
â
EVENT HANDL
ING
................................
................................
............................
330
27.
VB.NET
â
REGULAR EXP
RESSIONS
................................
................................
....................
336
28.
VB.NET
â
DATABASE ACCESS
................................
................................
...........................
350
29.
VB.NET
â
EXCEL SHEET
................................
................................
................................
....
365
30.
VB.NET
â
SEND EMAIL
................................
................................
................................
.....
370
31.
VB.NET
â
XML PROCESS
ING
................................
................................
.............................
376
32.
VB.NET
â
WEB PROGRAM
MING
................................
................................
......................
391
VB.NET
9V
isual Basic .NET (VB.NET) is an object
-
oriented computer programming language
implem
ented on the .NET Framework. Although it is an evolution of classic Visual Basic
language, it is not backwards
-
compatible with VB6, and any code written in the old version
does not compile under VB.NET.
Like all other .NET languages, VB.NET has complete su
pport for object
-
oriented concepts.
Everything in VB.NET is an object, including all of the primitive types (Short, Integer, Long,
String, Boolean, etc.) and user
-
defined types, events, and even assemblies. All objects
inherits from the base class Object.
VB.NET is implemented by Microsoft's .NET framework. Therefore, it has full access to all the
libraries in the .Net Framework. It's also possible to run VB.NET programs on Mono, the open
-
source alternative to .NET, not only under Windows, but even Linux or
Mac OSX.
The following reasons make VB.Net a widely used professional language:
ï·
Modern, general purpose.ï·
Object oriented.ï·
Component oriented.ï·
Easy to learn.ï·
Structured language.ï·
It produces efficient programs.ï·
It can be compiled on a variety of comp
uter platforms.ï·
Part of .Net Framework.
Strong Programming Features VB.Net
VB.Net has numerous strong programming features that make it endearing to multitude of
programmers worldwide. Let us mention some of these features:
ï·
Boolean Conditionsï·
Automatic G
arbage Collectionï·
Standard Library1.
VB.NET
â
Overview
VB.NET
10ï·
Assembly Versioning
ï·
Properties and Eventsï·
Delegates and Events Managementï·
Easy
-
to
-
use Genericsï·
Indexersï·
Conditional Compilationï·
Simple Multithreading
VB.NET
11I
n this chapter, we will discuss the
tools available for creating VB.Net applications.
We have already mentioned that VB.Net is part of .Net framework and used for writing .Net
applications. Therefore before discussing the available tools for running a VB.Net program,
let us understand how V
B.Net relates to the .Net framework.
The .Net Framework
The .Net framework is a revolutionary platform that helps you to write the following types of
applications:
ï·
Windows applicationsï·
Web applicationsï·
Web services
The .Net framework applications are mul
ti
-
platform applications. The framework has been
designed in such a way that it can be used from any of the following languages: Visual Basic,
C#, C++, Jscript, and COBOL, etc.
All these languages can access the framework as well as communicate with each o
ther.
The .Net framework consists of an enormous library of codes used by the client languages
like VB.Net. These languages use object
-
oriented methodology.
Following are some of the components of the .Net framework:
ï·
Common Language Runtime (CLR)ï·
The .Net
Framework Class Libraryï·
Common Language Specificationï·
Common Type Systemï·
Metadata and Assembliesï·
Windows Formsï·
ASP.Net and ASP.Net AJAXï·
ADO.Net2.
VB.NET
â
Environment
Setup
VB.NET
12ï·
Windows Workflow Foundation (WF)ï·
Windows Presentation Foundationï·
Windows Communication Foundation (WCF
)ï·
LINQ
For the jobs each of these components perform, please see
ASP.Net
-
Introduction
,
and for
details of each component, please consult Microsoft's documentation.
Integrated Development
Environment (IDE) For VB.Net
Microsoft provides the following development tools for VB.Net programming:
ï·
Visual Studio 2010 (VS)ï·
Visual Basic 2010 Express (VBE)ï·
Visual Web Developer
The last two are free. Using these tools, you can write all kinds of VB.N
et programs from
simple command
-
line applications to more complex applications. Visual Basic Express and
Visual Web Developer Express edition are trimmed down versions of Visual Studio and has
the same look and feel. They retain most features of Visual Stu
dio. In this tutorial, we have
used Visual Basic 2010 Express and Visual Web Developer (for the web programming
chapter).
You can download it
from
here
. It gets automatically
i
nstalled in your machine. Please note
that you need an active internet connection for installing the express edition.
Writing VB.Net Programs on Linux or Mac OS
Although the
.NET Framework runs on the Windows operating system, there are some
alternative ve
rsions that work on other operating systems. Mono is an open
-
source version
of the .NET Framework which includes a Visual Basic compiler and runs on several operating
systems, including various flavors of Linux and Mac OS. The most recent version is VB 201
2.
The stated purpose of Mono is not only to be able to run Microsoft .NET applications cross
-
platform, but also to bring better development tools to Linux developers. Mono can be run on
many operating systems including Android, BSD, iOS, Linux, OS X, Wind
ows, Solaris and
UNIX.
VB.NET
13B
efore we study basic building blocks of the VB.Net programming language, let us look a bare
minimum VB.Net program structure so that we can take it as a reference in upcoming
chapters.
VB.Net Hello World E
xample
A VB.Net program basically consists of the following parts:
ï·
Namespace declarationï·
A class or moduleï·
One or more proceduresï·
Variablesï·
The Main procedureï·
Statements & Expressionsï·
Comments
Let us look at a simple code that would print the words "
Hello World":
Imports System
Module Module1
'This program will display Hello World
Sub Main()
Console.WriteLine("Hello World")
Console.ReadKey()
End Sub
End Module
When the above code is compiled and executed, it produces the followin
g result:
Hello, World!3.
VB.NET
â
Program Structure
VB.NET
14Let us look various parts of the above program:
ï·
The first line of the program
Imports System
is used to include the System
namespace in the program.
ï·
The next line has a
Module
declaration, the module
Module1
. VB.Net is completely
ob
ject oriented, so every program must contain a module of a class that contains the
data and procedures that your program uses.ï·
Classes or Modules generally would contain more than one procedure. Procedures
contain the executable code, or in other words, t
hey define the behavior of the class.
A procedure could be any of the following:
o
Functiono
Subo
Operatoro
Geto
Seto
AddHandlero
RemoveHandlero
RaiseEvent
ï·
The next line
(
'This program) will be ignored by the compiler and it has been put to
add additional co
mments in the program.ï·
The next line defines the Main procedure, which is the entry point for all VB.Net
programs. The Main procedure states what the module or class will do when executed.ï·
The Main procedure specifies its behavior with the statement
Cons
ole.WriteLine
("Hello World")
WriteLine
is a method of the
Console
class
defined in the
System
namespace. This statement causes the message "Hello, World!"
to be displayed on the screen.ï·
The last line
Console.ReadKey()
is for the VS.NET Users. This will p
revent the screen
from running and closing quickly when the program is launched from Visual
Studio .NET.
Compile & Execute VB.Net Program
If you are using Visual Studio.Net IDE, take the following steps:
ï·
Start Visual Studio.
VB.NET
15ï·
On the menu bar, choose File
ï
New
ï
Project.ï·
Choose Visual Basic from templatesï·
Choose Console Application.ï·
Specify a name and location for your project using the Browse button, and then choose
the OK button.ï·
The new project appears in Solution Explorer.ï·
Write code in the Code Ed
itor.ï·
Click the Run button or the F5 key to run the project. A Command Prompt window
appears that contains the line Hello World.
You can compile a VB.Net program by using the command line instead of the Visual Studio
IDE:
ï·
Open a text editor and add the ab
ove mentioned code.ï·
Save the file as
helloworld.vbï·
Open the command prompt tool and go to the directory where you saved the file.ï·
Type
vbc helloworld.vb
and press enter to compile your code.ï·
If there are no errors in your code the command prompt will t
ake you to the next line
and would generate
helloworld.exe
executable file.ï·
Next, type
helloworld
to execute your program.ï·
You will be able to see "Hello World" printed on the screen.
VB.NET
16V
B.Net is an object
-
oriented programming languag
e. In Object
-
Oriented Programming
methodology, a program consists of various objects that interact with each other by means
of actions. The actions that an object may take are called methods. Objects of the same kind
are said to have the same type or, more
often, are said to be in the same class.
When we consider a VB.Net program, it can be defined as a collection of objects that
communicate via invoking each other's methods. Let us now briefly look into what do class,
object, methods
,
and instant variables
mean.
ï·
Object
-
Objects have states and behaviors. Example: A dog has states
-
color, name,
breed as well as behaviors
-
wagging, barking, eating, etc. An object is an instance of
a class.ï·
Class
-
A class can be defined as a template/blueprint that descri
bes the
behaviors/states that object of its type support.ï·
Methods
-
A method is basically a behavior. A class can contain many methods. It is
in methods where the logics are written, data is manipulated and all the actions are
executed.ï·
Instant Variables
-
Each object has its unique set of instant variables. An object's
state is created by the values assigned to these instant variables.
A Rectangle Class in VB.Net
For example, let us consider a Rectangle object. It has attributes like length and width.
De
pending upon the design, it may need ways for accepting the values of these attributes,
calculating area and displaying details.
Let us look at an implementation of a Rectangle class and discuss VB.Net basic syntax on the
basis of our observations in it:
I
mports System
Public Class Rectangle
Private length As Double
Private width As Double
'Public methods
Public Sub AcceptDetails()
4.
VB.NET
â
Basic Syntax
VB.NET
17
length = 4.5
width = 3.5
End Sub
Public Function GetArea() As Double
GetArea
= length * width
End Function
Public Sub Display()
Console.WriteLine("Length: {0}", length)
Console.WriteLine("Width: {0}", width)
Console.WriteLine("Area: {0}", GetArea())
End Sub
Shared Sub Main()
Dim r A
s New Rectangle()
r.Acceptdetails()
r.Display()
Console.ReadLine()
End Sub
End Class
When the above code is compiled and executed, it produces the following result:
Length: 4.5
Width: 3.5
Area: 15.75
In previous chapter, we crea
ted a Visual Basic module that held the code. Sub Main indicates
the entry point of VB.Net program. Here, we are using Class that contains both code and data.
You use classes to create objects. For example, in the code, r is a Rectangle object.
An object i
s an instance of a class:
Dim r As New Rectangle()
A class may have members that can be accessible from outside class, if so specified. Data
members are called fields and procedure members are called methods.
VB.NET
18Shared
methods or
static
methods can be invoked
without creating an object of the class.
Instance methods are invoked through an object of the class:
Shared Sub Main()
Dim r As New Rectangle()
r.Acceptdetails()
r.Display()
Console.ReadLine()
End Sub
Identifiers
An identifier is a name used
to identify a class, variable, function, or any other user
-
defined
item. The basic rules for naming classes in VB.Net are as follows:
ï·
A name must begin with a letter that could be followed by a sequence of letters, digits
(0
-
9) or underscore. The first c
haracter in an identifier cannot be a digit.ï·
It must not contain any embedded space or symbol like ?
-
+! @ # % ^ & * ( ) [ ]
{ } . ; : " ' / and
\
. However, an underscore ( _ ) can be used.ï·
It should not be a reserved keyword.
VB.Net Keywords
The follow
ing table lists the VB.Net reserved keywords:
AddHandler
AddressOf
Alias
And
AndAlso
As
Boolean
ByRef
Byte
ByVal
Call
Case
Catch
CBool
CByte
CChar
CDate
CDec
CDbl
Char
CInt
Class
CLng
CObj
Const
Continue
CSByte
CShort
CSng
CStr
CType
CUInt
CULng
CUShor
t
Date
Decimal
Declare
Default
Delegate
Dim
DirectCast
Do
VB.NET
19D
ouble
Each
Else
ElseIf
End
End If
Enum
Erase
Error
Event
Exit
False
Finally
For
Friend
Function
Get
GetType
GetXML
Namespace
Global
GoTo
Handles
If
Implements
Imports
In
Inherits
Integer
Inte
rface
Is
IsNot
Let
Lib
Like
Long
Loop
Me
Mod
Module
MustInherit
MustOverride
MyBase
MyClass
Namespace
Narrowing
New
Next
Not
Nothing
Not
Inheritable
Not
Overridable
Object
Of
On
Operator
Option
Optional
Or
OrElse
Overloads
Overridable
Overrides
ParamAr
ray
Partial
Private
Property
Protected
Public
RaiseEvent
ReadOnly
ReDim
REM
Remove
Handler
Resume
Return
SByte
Select
Set
Shadows
Shared
Short
Single
Static
Step
Stop
String
Structure
Sub
SyncLock
Then
Throw
To
True
Try
TryCast
TypeOf
UInteger
While
Widening
With
WithEvents
WriteOnly
Xor
VB.NET
20D
ata types refer to an extensive system used for declaring variables or functions of different
types. The type of a variable determines how much space it occupies in storage and how the
bit pa
ttern stored is interpreted.
Data Types Available in VB.Net
VB.Net provides a wide range of data types. The following table shows all the data types
available:
Data Type
Storage Allocation
Value Range
Boolean
Depends on
implementing
platform
True
or
False
Byte
1 byte
0 through 255 (unsigned)
Char
2 bytes
0 through 65535 (unsigned)
Date
8 bytes
0:00:00 (midnight) on January 1, 0001 through
11:59:59 PM on December 31, 9999
Decimal
16 bytes
0 through +/
-
79,228,162,514,264,337,593,543,950,335
(+/
-
7.9...E+2
8) with no decimal point; 0
through +/
-
7.9228162514264337593543950335 with 28
places to the right of the decimal
Double
8 bytes
-
1.79769313486231570E+308 through
-
4.94065645841246544E
-
324, for negative
values
4.94065645841246544E
-
324 through
1.79769313486
231570E+308, for positive
values
5.
VB.NET
â
Data Types
VB.NET
21Integer
4 bytes
-
2,147,483,648 through 2,147,483,647
(signed)
Long
8 bytes
-
9,223,372,036,854,775,808 through
9,223,372,036,854,775,807(signed)
Object
4 bytes on 32
-
bit
platform
8 bytes on 64
-
bit
platform
Any type can be
stored in a variable of type
Object
SByte
1 byte
-
128 through 127 (signed)
Short
2 bytes
-
32,768 through 32,767 (signed)
Single
4 bytes
-
3.4028235E+38 through
-
1.401298E
-
45 for
negative values;
1.401298E
-
45 through 3.4028235E+38 for
positive values
St
ring
Depends on
implementing
platform
0 to approximately 2 billion Unicode characters
UInteger
4 bytes
0 through 4,294,967,295 (unsigned)
ULong
8 bytes
0 through 18,446,744,073,709,551,615
(unsigned)
User
-
Defined
Depends on
implementing
platform
Each me
mber of the structure has a range
determined by its data type and independent of
the ranges of the other members
UShort
2 bytes
0 through 65,535 (unsigned) VB.NET
22Example
The following example demonstrates use of some of the types:
Module DataTypes
Sub Mai
n()
Dim b As Byte
Dim n As Integer
Dim si As Single
Dim d As Double
Dim da As Date
Dim c As Char
Dim s As String
Dim bl As Boolean
b = 1
n = 1234567
si = 0.12345678901234566
d = 0.1234
5678901234566
da = Today
c = "U"c
s = "Me"
If ScriptEngine = "VB" Then
bl = True
Else
bl = False
End If
If bl Then
'the oath taking
Console.Write(c & " and," & s & vbCrLf)
Console.WriteLine("declaring on the day of: {0}", da)
Console.WriteLine("We will learn VB.Net seriously")
Console.WriteLine("Lets see what happens to the floating point
variables:")
Console.WriteLine("The Single: {0}, The
Double: {1}", si, d)
End If
VB.NET
23
Console.ReadKey()
End SubEnd Module
When the above code is compiled and executed, it produces the following result:
U and, Me
declaring on the day of: 12/4/2012 12:00:00 PM
We will learn VB.Net seriously
Lets s
ee what happens to the floating point variables:
The Single:0.1234568, The Double: 0.123456789012346
The Type Conversion Functions in VB.Net
VB.Net provides the following in
-
line type conversion functions:
S.N
Functions & Description
1
CBool(expression)
C
onverts the expression to Boolean data type.
2
CByte(expression)
Converts the expression to Byte data type.
3
CChar(expression)
Converts the expression to Char data type.
4
CDate(expression)
Converts the expression to Date data type
5
CDbl(expression)
Converts the expression to Double data type.
VB.NET
246
CDec(expression)
Converts the expression to Decimal data type.
7
CInt(expression)
Converts the expression to Integer data type.
8
CLng(expression)
Converts the expression to Long data type.
9
CObj(expressi
on)
Converts the expression to Object type.
10
CSByte(expression)
Converts the expression to SByte data type.
11
CShort(expression)
Converts the expression to Short data type.
12
CSng(expression)
Converts the expression to Single data type.
13
CStr(exp
ression)
Converts the expression to String data type.
14
CUInt(expression)
Converts the expression to UInt data type.
15
CULng(expression)
Converts the expression to ULng data type.
VB.NET
2516
CUShort(expression)
Converts the expression to UShort data type.
Example
The following example demonstrates some of these functions:
Module DataTypes
Sub Main()
Dim n As Integer
Dim da As Date
Dim bl As Boolean = True
n = 1234567
da = Today
Console.WriteLine(bl)
Console.Write
Line(CSByte(bl))
Console.WriteLine(CStr(bl))
Console.WriteLine(CStr(da))
Console.WriteLine(CChar(CChar(CStr(n))))
Console.WriteLine(CChar(CStr(da)))
Console.ReadKey()
End Sub
End Module
When the above code is compiled and e
xecuted, it produces the following result:
True
-
1
True
12/4/20121
1
VB.NET
26A
variable is nothing but a name given to a storage area that our programs can manipulate.
Each variable in VB.Net has a specific type, which determines the size and
layout of the
variable's memory; the range of values that can be stored within that memory; and the set
of operations that can be applied to the variable.
We have already discussed various data types. The basic value types provided in VB.Net can
be categor
ized as:
Type
Example
Integral types
SByte, Byte, Short, UShort, Integer, UInteger, Long, ULong and
Char
Floating point types
Single and Double
Decimal types
Decimal
Boolean types
True or False values, as assigned
Date types
DateVB.Net also allows
defining other value types of variable like
Enum
and reference types of
variables like
Class
. We will discuss date types and Classes in subsequent chapters.
Variable Declaration in VB.Net
The
Dim
statement is used for variable declaration and storage alloc
ation for one or more
variables. The Dim statement is used at module, class, structure, procedure
,
or block level.
Syntax for variable declaration in VB.Net is:
[ ibute&#x att;&#xr120;list ] [ accessmodifier ] [[ Shared ] [ Shadows ] | [ Static ]]
[ ReadOnly ] Dim
[ WithEvents ] variablelist
Where,
ï·
attributelist
is a list of attributes that apply to the variable. Optional.
6.
VB.NET
â
Variables
VB.NET
27
ï·
accessmodifier
defines the access levels of the variables, it has values as
-
Public,
Protected, Friend, Protected Friend and Private. Optional.ï·
Shared
declares a shared variable, which is not associated with any specific instance
of a class or structure, rather available to all the instances of the class or structure.
Optional.ï·
Shadows
indicate that the variable re
-
declares and hides an identic
ally named
element, or set of overloaded elements, in a base class. Optional.ï·
Static
indicates that the variable will retain its value, even when the after termination
of the procedure in which it is declared. Optional.ï·
ReadOnly
means the variable can be
read, but not written. Optional.ï·
WithEvents
specifies that the variable is used to respond to events raised by the
instance assigned to the variable. Optional.ï·
Variablelist
provides the list of variables declared.
Each variable in the variable list has
the following syntax and parts:
variablename[ ( [ boundslist ] ) ] [ As [ New ] datatype ] [ = initializer ]
Where,
ï·
variablename
: is the name of the variableï·
boundslist
: optional. It provides list of bounds of each dimension of an array variable.ï·
New
: op
tional. It creates a new instance of the class when the Dim statement runs.ï·
datatype
: Required if Option Strict is On. It specifies the data type of the variable.ï·
initializer
: Optional if New is not specified. Expression that is evaluated and assigned
to
the variable when it is created.
Some valid variable declarations along with their definition are shown here:
Dim StudentID As Integer
Dim StudentName As String
Dim Salary As Double
Dim count1, count2 As Integer
Dim status As Boolean
Dim exitButton As New
System.Windows.Forms.Button
VB.NET
28Dim lastTime, nextTime As Date
Variable Initialization in VB.Net
Variables are initialized (assigned a value) with an equal sign followed by a constant
expression. The general form of initialization is:
variable_name = value;
f
or example,
Dim pi As Double
pi = 3.14159
You can initialize a variable at the time of declaration as follows:
Dim StudentID As Integer = 100
Dim StudentName As String = "Bill Smith"
Example
Try the following example which makes use of various types of var
iables:
Module variablesNdataypes
Sub Main()
Dim a As Short
Dim b As Integer
Dim c As Double
a = 10
b = 20
c = a + b
Console.WriteLine("a = {0}, b = {1}, c = {2}", a, b, c)
Console.ReadLine()
End Sub
En
d Module VB.NET
29When the above code is compiled and executed, it produces the following result:
a = 10, b = 20, c = 30
Accepting Values from User
The Console class in the System namespace provides a function
ReadLine
for accepting input
from the user and store
it into a variable. For example,
Dim message As String
message = Console.ReadLine
The following example demonstrates it:
Module variablesNdataypes
Sub Main()
Dim message As String
Console.Write("Enter message: ")
message = Console.Read
Line
Console.WriteLine()
Console.WriteLine("Your Message: {0}", message)
Console.ReadLine()
End Sub
End Module
When the above code is compiled and executed, it produces the following result (assume the
user inputs Hello World):
Enter m
essage: Hello World
Your Message: Hello World
Lvalues and Rvalues
There are two kinds of expressions:
ï·
lvalue :
An expression that is an lvalue may appear as either the left
-
hand or right
-
hand side of an assignment.ï·
rvalue :
An expression that is an rva
lue may appear on the right
-
but not left
-
hand
side of an assignment.
VB.NET
30Variables are lvalues and so may appear on the left
-
hand side of an assignment. Numeric
literals are rvalues and so may not be assigned and can not appear on the left
-
hand side.
Followin
g is a valid statement:
Dim g As Integer = 20
But following is not a valid statement and would generate compile
-
time error:
20 = g VB.NET
31End of ebook preview
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