Wednesday, 19 March 2014

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 describe 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 display 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:
AddHandlerAddressOfAliasAndAndAlsoAsBoolean
ByRefByteByValCallCaseCatchCBool
CByteCCharCDateCDecCDblCharCInt
ClassCLngCObjConstContinueCSByteCShort
CSngCStrCTypeCUIntCULngCUShortDate
DecimalDeclareDefaultDelegateDimDirectCastDo
DoubleEachElseElseIfEndEnd IfEnum
EraseErrorEventExitFalseFinallyFor
FriendFunctionGetGetTypeGetXML
Namespace
GlobalGoTo
HandlesIfImplementsImportsInInheritsInteger
InterfaceIsIsNotLetLibLikeLong
LoopMeModModuleMustInheritMustOverrideMyBase
MyClassNamespaceNarrowingNewNextNotNothing
Not
Inheritable
Not
Overridable
ObjectOfOnOperatorOption
OptionalOrOrElseOverloadsOverridableOverridesParamArray
PartialPrivatePropertyProtectedPublicRaiseEventReadOnly
ReDimREMRemove
Handler
ResumeReturnSByteSelect
SetShadowsSharedShortSingleStaticStep
StopStringStructureSubSyncLockThenThrow
ToTrueTryTryCastTypeOfUIntegerWhile
WideningWithWithEventsWriteOnlyXor

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 TypeStorage AllocationValue Range
BooleanDepends on implementing platformTrue or False
Byte1 byte0 through 255 (unsigned)
Char2 bytes0 through 65535 (unsigned)
Date8 bytes0:00:00 (midnight) on January 1, 0001 through 11:59:59 PM on December 31, 9999
Decimal16 bytes0 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
Integer4 bytes-2,147,483,648 through 2,147,483,647 (signed)
Long8 bytes-9,223,372,036,854,775,808 through 9,223,372,036,854,775,807(signed)
Object4 bytes on 32-bit platform 8 bytes on 64-bit platform Any type can be stored in a variable of type Object
SByte1 byte-128 through 127 (signed)
Short2 bytes-32,768 through 32,767 (signed)
Single4 bytes-3.4028235E+38 through -1.401298E-45 for negative values;1.401298E-45 through 3.4028235E+38 for positive values
StringDepends on implementing platform0 to approximately 2 billion Unicode characters
UInteger4 bytes0 through 4,294,967,295 (unsigned)
ULong8 bytes0 through 18,446,744,073,709,551,615 (unsigned)
User-DefinedDepends on implementing platformEach member of the structure has a range determined by its data type and independent of the ranges of the other members
UShort2 bytes0 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 inline type conversion functions:
S.NFunctionss & Description
1CBool(expression)
Converts the expression to Boolean data type.
2CByte(expression)
Converts the expression to Byte data type.
3CChar(expression)
Converts the expression to Char data type.
4CDate(expression)
Converts the expression to Date data type
5CDbl(expression)
Converts the expression to Double data type.
6CDec(expression)
Converts the expression to Decimal data type.
7CInt(expression)
Converts the expression to Integer data type.
8CLng(expression)
Converts the expression to Long data type.
9CObj(expression)
Converts the expression to Object type.
10CSByte(expression)
Converts the expression to SByte data type.
11CShort(expression)
Converts the expression to Short data type.
12CSng(expression)
Converts the expression to Single data type.
13CStr(expression)
Converts the expression to String data type.
14CUInt(expression)
Converts the expression to UInt data type.
15CULng(expression)
Converts the expression to ULng data type.
16CUShort(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
 
 
 
 
Source : http://www.tutorialspoint.com 

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