Monday, 25 July 2016
VB.Net - Basic Syntax
VB.Net is an object-oriented programming language. 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.
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.
Class - A class can be defined as a template/blueprint that describes the behaviors/states that object of its type support.
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.
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. Depending 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:
Imports System
Public Class Rectangle
Private length As Double
Private width As Double
'Public methods
Public Sub AcceptDetails()
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 As 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 created 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 is 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.
Shared 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:
A name must begin with a letter that could be followed by a sequence of letters, digits (0 - 9) or underscore. The first character in an identifier cannot be a digit.
It must not contain any embedded space or symbol like ? - +! @ # % ^ & * ( ) [ ] { } . ; : " ' / and \. However, an underscore ( _ ) can be used.
It should not be a reserved keyword.
VB.Net Keywords
The following 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 CUShort Date
Decimal Declare Default Delegate Dim DirectCast Do
Double 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
Interface 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 ParamArray
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 - Data Types
Data 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 pattern 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+28) 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 1.79769313486231570E+308, for positive values
Integer 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
String 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 member 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)
Example
The following example demonstrates use of some of the types:
Module DataTypes
Sub Main()
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 = 0.12345678901234566
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
Console.ReadKey()
End Sub
End 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 see 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)
Converts 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.
6
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(expression)
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(expression)
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.
16
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.WriteLine(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 executed, it produces the following result:
True
-1
True
12/4/2012
1
1
vb.net programming
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