unit 2 vb variables

8/13/2019 Unit 2 VB Variables

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Vipul J JoshiNarsinhbhai Institute of Computer Studies and Management(NICM)

Kadi


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A storage location in memory (RAM)

Holds data/information while the program is running

These storage locations can be referred to by their

names

Every variable has three properties:

Name- reference to the location - cannot be changed

Value- the information that is stored - can be changedduring program execution, hence the name variable

Data Type- the type of information that can be stored -

cannot be changed


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You the programmer make up a name for thevariable

Visual Basic associates that name with alocation in the computer's RAM

The value currently associated with thevariable is stored in that memory location

You simply use the name you choose whenyou need to access the value


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Copy and store values entered by the user Perform arithmetic manipulation on values

Test values to see if they meet a criteria Temporarily hold and manipulate the value of

a control property Hold data/information so that it can be

recalled for use at a later point in the code


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Data type - Specifies type of data variable can store Integer variables: Long, Integer, Short, Byte Floating-point variables: Single, Double

Fixed decimal point variable: Decimal Boolean variables: True, False

Character variable: Char

Text variable: String

The Object variable Default data type assigned by Visual Basic

Can store many different types of data

Less efficient than other data types


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Data type Prefix Size ValuesByte byt 1 byte positive integer value from 0 to 255Short shr 2 byte integer from 32,768 to +32,767Integer int 4 byte integer from +/- 2,147,483,647

Long lng 8 byte integer from +/- 9,223,372,036,854,775,807Single sng 4 byte single-precision, floating-point numberDouble dbl 8 byte double-precision, floating-point numberDecimal dec 16 byte number with up to 28 significant digits

Char chr 2 byte Any single characterBoolean bln 2 byte True or False

String str (4 byte) Text - Any number/combination of charactersDate dtm 8 byte 8 character date: #dd/mm/yyyy#Object obj (4 byte) An address that refers to an object


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First character must be a letter or underscore Must contain only letters, numbers, and

underscores (no spaces, periods, etc.)

Can have up to 255 characters Cannot be a VB language keyword Naming Conventions Should be meaningful

Follow 3 char prefix style - 1st 3 letters in lowercaseto indicate the data type

After that, capitalize the first letter of each word

Example: intTestScore


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A variable declaration is a statement thatcreates a variable in memory

Syntax: Dim VariableNameAs DataType Dim (short for Dimension) - keyword

VariableName - name used to refer to variable

As - keyword DataType - one of many possible keywords to

indicate the type of value the variable will contain

Example: Dim intLength as Integer


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A starting or initialization value may bespecified with the Dim statement

Good practice to set an initial value unlessassigning a value prior to using the variable Syntax:

Dim VariableNameAs DataType= Value Just append " = value to the Dim statement

= 5assigning a beginning value to the variable

Example: Dim intLength as Integer = 5


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Variable MUST be declared prior to the codewhere they are used

Variable should be declared first in theprocedure (style convention)

Declaring an initial value of the variable in thedeclaration statement is optional

Refer to default values (next slide)


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Data type Default (Initial) value

All numeric types Zero (0)

Boolean FalseChar Binary 0

String or Object Empty

Date 12:00 a.m. on January 1, 0001


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Actual value/data/information Similar to a variable, but can NOT change

during the execution of a program. Examples of Literals:

Numeric: 5 ; 157 ; 195.38256

String: Paul ; Hello!!! ; Jackson, AL 36545

Char: a ; 1 ; ? ; @

Boolean: True ; False


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Programs often need to use given values

For example: decTotal *= 1.06

Adds 6% sales tax to an order total

Two problems with using literals for these typesof values

The reason for multiplying decTotal by 1.06 isnt

always obvious

If sales tax rate changes, must find and change every

occurrence of .06 or 1.06


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Use of named constantsresolves both these issues Can declare a variable whose value is set at

declaration and cannot be changed later: Syntax: Const CONST_NAMEAs DataType= Value

Looks like a normal declaration except:

Const used instead of Dim

An initialization value is required

By convention, entire name capitalized with underscore

characters to separate words


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The objective of our code is now clearer

Const sngSALES_TAX_RATE As Single = 1.06

decTotal *= sngSALES_TAX_RATE Can change all occurrences in the code simply

by changing the initial value set in thedeclaration

If tax rate changes from 6% to 7%

Const sngSALES_TAX_RATE As Single = 1.07


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What Indicates the part of the program where thevariable can be used

When From the variable declaration until the end ofthe code block (procedure, method, etc.) where it is

declared Variable cannot be used before it is declared

Variable declared within a code block is only visible tostatements within that code block

Called Local Variable Can be declared at the beginning of the class code window

(General Declarations section) and be available to all blocks Called Form Level Variable

Variables that share the same scope cannot have the samename (same name ok if different scope)


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What Indicates the part of the program where the

variable exists in memory When From the beginning of the code block

(procedure, method, etc.) where it is declared untilthe end of that code block

When the code block begins the space is created to holdthe local variables

Memory is allocated from the operating system When the code block ends the local variables are destroyed

Memory is given back to the operating system


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Syntax: variablename = expression Assigns the value of the expression to the

variable. (The variable must be on the left andthe expression on the right.)

Example: intNumber1 = 4

intNumber2 = 3 * (2 + 2) intNumber3 = intNumber1

IntNumber1 = intNumber1 + 6


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A value of one data type can be assigned to a variable

of a different type

An implicit type conversion is an attempt to automatically

convert to the receiving variables data type A widening conversion suffers no loss of data

Converting an integer to a single

Dim sngNumber as Single = 5

A narrowing conversion may lose data Converting a decimal to an integer

Dim intCount = 12.2 intCount becomes 12


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VB provides a set of functions that perform data type

conversions These functions will accept a literal, variable name, or

arithmetic expression The following narrowing conversions require an

explicit type conversion

Double to Single

Single to Integer Long to Integer

Boolean, Date, Object, String, and numeric types

represent different sorts of values and require

conversion functions as well


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Ctype Usage

CBool Convert to Booldata type

CByte Convert to Bytedata type

CChar Convert to Chardata type

CDate Convert to Datedata type

CDbl Convert to Doubledata type

CDec Convert to Decimaldata type

CInt Convert to Intdata type

CLng Cpnvert to LongtypeCObj Convert to Objecttype

CShort Convert to Shortdata type

CSng Convert to Singledata type

CStr Convert to Stringtype

CType (converting Var,Datatype)

CType is compiled in-line, meaning theconversion code is part of the code thatevaluates the expression. Execution is fasterbecause there is no call to procedure toperform the conversion


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The Val functionis a more forgiving means ofperforming string to numeric conversions

Uses the form Val(string) If the initial characters form a numeric value,

the Val function will return that Otherwise, it will return a value of zero


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Val Function Value Returned

Val("34.90) 34.9

Val("86abc) 86

Val("$24.95) 0

Val("3,789) 3

Val(") 0

Val("x29) 0

Val("47%) 47

Val("Geraldine) 0


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Returns a string representation of the value inthe variable calling the method

Every VB data type has a ToString()method Uses the form VariableName.ToString For example

Dim number as Integer = 123lblNumber.text = number.ToString

Assigns the string 123 to the text property of the

lblNumber control


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Dim Amnt As Single = 9959.95

Dim strAmnt As String

strAmnt = Amnt.ToString(C)Or use the following picture numeric format string:

strAmnt = Amnt.ToString($#,###.00)

Output:

Both statements will format the value as $9,959.95.


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Dim Amount As Decimal = 42492.45

Debug.WriteLine(Amount.ToString($#,###.00))

$42,492.45

Amount = 0.2678

Debug.WriteLine(Amount.ToString(0.000))

0.268

Amount = -24.95

Debug.WriteLine(Amount.ToString

($#,###.00;($#,###.00)))

($24.95)


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We used variables to store individual values. As a matter offact, most programs store sets of data of different types. Forexample, a program for balancing your checkbook must

store several pieces of information for each check: thechecksnumber, amount, date, and so on. All these pieces ofinformation are necessary to process the checks, and ideally,they should be stored together.

You can create custom data types that are made up of

multiple values using structures. A VB structure allowsyou to combine multiple values of the basic data types andhandle them as a whole. For example, each check in acheckbook-balancing application is stored in a separate

structure


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Syntax:[ Public | Protected | Friend | Protected Friend |Private]

Structure structName

Dim variable1 As varTypeDim variable2 As varType

...

Dim variablen As varType

End Structure

In the above syntax structName is the name of the user defined datatype,that follows the naming convention of a variable. Publicoption makes thesedatatypes available in all projects, modules, classes. If declared Private theuser defined datatypes can be used where it is declared, same applies toFriendand Protected Friend. variable1is the name of the element of an userdefined datatype. typeis the primitive datatype available in visual basic


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Example:Structure Empdetails

Dim EmpNo As Integer

Dim EmpName As String

Dim EmpSalary As IntegerDim EmpExp As Integer

End Structure

*Event Scope

Dim TotalSal As Empdetails

TotalSal.EmpNo = TextBox1.TextTotalSal.EmpName = TextBox2.Text

TotalSal.EmpSalary = TextBox3.Text

TotalSal.EmpExp = TextBox4.Text

TextBox5.Text = Val(TotalSal.EmpSalary) *

Val(TotalSal.EmpExp)*End of Event Scope


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A standard structure for storing data in anyprogramming language is the array.

Whereas individual variables can hold singleentities, such as one number, one date, orone string

Arrays can hold sets of data of the same type(a set of numbers, a series of dates, and soon). An array has a name, as does a variable,and the values stored in it can be accessed by

an index.


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Unlike simple variables, arrays must bedeclared with the Dim (or Public) statement

followed by the name of the array and theindex of the last element in the array inparenthesesfor example:

Dim intSalary(15) as Integer

It holds the value of 16 persons. To assignvalues you can write

intSalary(0) = 25000


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Arrays, like variables, are not limited to thebasic data types. You can declare arrays thathold any type of data, including objects.

The other way to store multiple values is byusing structure

Dim colors(2) As Colorcolors(0) = Color.BurlyWood

colors(1) = Color.AliceBlue

colors(2) = Color.Sienna

Structure Employee

Dim Name As String

Dim Salary As Decimal

End Structure

Dim Emps(15) As Employee

Emps(2).Name = Hello All

Emps(2).Salary = 62000


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Just as you can initialize variables in the sameline in which you declare them, you can

initialize arrays, too, with the followingconstructor.Dim arrayname() As type = { entry0, entry1, ...

entryN }

Dim Names() As String = {Hello,All}

This statement is equivalent to the followingstatements

Dim Names(1) As String

Names(0) = Hello

Names(1) = All


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The first element of an array has index 0. The number thatappears in parentheses in the Dimstatement is one fewer than

the arraystotal capacity and is the arraysupper limit (or upper

bound). The index of the last element of an array (its upperbound) is given by the method GetUpperBound, which

accepts as an argument the dimension of the array and returnsthe upper bound for this dimension. The arrays we examined sofar are one-dimensional and the argument to be passed to the

GetUpperBound method is the value 0. The total number ofelements in the array is given by the method GetLength,

which also accepts a dimension as an argument. The upperbound of the following array is 19, and the capacity of the array

is 20 elements:


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Dim Names(19) As Integer

The first element is Names(0), and the last isNames(19).

Debug.WriteLine(Names.GetLowerBound(0))Output: 0

Debug.WriteLine(Names.GetUpperBound(0))

Output: 19

You can also use length() property of arrayto retrieve the count of element


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Dim a(,) As Integer = {{10, 20, 30}, {11, 21, 31},

{12, 22, 32}}

Console.WriteLine(a(0, 1)) will print 20

Console.WriteLine(a(2, 2)) will print 32

Debug.WriteLine(numbers.Rank

)2 dimensions in array


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Dynamic arrays are array that are declaredusing a Dim statement with blank parenthesis

initially and are dynamically allocateddimensions using the Redimstatement. ThePreserve keyword is used with Redim

to preserve the existing elements intake.


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Module Module1

Sub Main()

Dim a() As Integer = {2, 2}

Dim i, j As Integer

Console.WriteLine("Array before Redim")

For i = 0 To a.GetUpperBound(0)Console.WriteLine(a(i))

Next

ReDim Preserve a(5)

Console.WriteLine("Array after Redim")

For j = 0 To a.GetUpperBound(0)

Console.WriteLine(a(j))

Next

Console.ReadLine()

End Sub

End Module


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Arithmetic Operators

^ Exponential

* Multiplication

/ Floating Point Division

\ Integer Division

MOD Modulus (remainder from division)

+ Addition

Subtraction

& String Concatenation (putting them together)


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Examples of use: decTotal = decPrice + decTax

decNetPrice = decPrice - decDiscount

dblArea = dblLength * dblWidth

sngAverage = sngTotal / intItems

dblCube = dblSide ^ 3


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The backslash (\) is used as an integer divisionoperator

The result is always an integer, created bydiscarding any remainder from the division

Example intResult = 7 \ 2 result is 3

shrHundreds = 157 \ 100 result is 1 shrTens = (157 - 157 \ 100 * 100) \ 10

result is ?


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This operator can be used in place of thebackslash operator to give the remainder of a

division operationintRemainder = 17 MOD 3 result is 2

dblRemainder = 17.5 MOD 3 result is 2.5

Any attempt to use of the \ or MOD operatorto perform integer division by zero causes aDivideByZeroException runtime error


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Concatenate: connect strings together Concatenation operator: the ampersand (&) Include a space before and after the & operator

Numbers after & operator are converted to strings

How to concatenate character strings strFName = "Bob"

strLName = "Smith"

strName = strFName & " Bob

strName = strName & strLName Bob Smith

intX = 1 intY = 2

intResult = intX + intY

strOutput = intX & + & intY & = & intResult 1 + 2 = 3


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Operatorprecedencetells us the order in whichoperations are performed

From highest to lowest precedence:

Exponentiation (^) Multiplicative (* and /)

Integer Division (\)

Modulus (MOD)

Additive (+ and -) Parentheses override the order of precedence Where precedence is the same, operations

occur from left to right


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Parenthesis Exponential

Multiplication / Division Integer Division MOD Addition / Subtraction String Concatenation Relational Operators (< , > , >= ,


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6 * 2 ^ 3 + 4 / 2 = 50

7 * 4 / 26 = 8

5 * (4 + 3)15 Mod 2 = 34

intX = 10

intY = 5

intResultA = intX + intY * 5 'iResultA is 35

iResultB = (intX + intY) * 5 'iResultB is 75 dResultA = intX - intY * 5 'dResultA is -15 dResultB = (intX - intY) * 5 'dResultB is 25


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It will execute some logic when a conditionbecome true goes to If and some other logic

when the condition is false goes to Else. It is always perform results for comparison of

two values.Ifcondition Then

Logic...ElseIfcondition-n Then

Logic...

Else

Logic....

End If


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If IsNumeric(txtNo.Text) ThenlblAns.Text = Yes its Numeric

End If

If txtNo.Text Mod 2 =0 Then

lblAns.Text = Its Even

ElselblAns.Text = Its Odd

End If

n1= txtNo1.Text

n2= txtNo2.Text

If no1 > no2 ThenlblAns.Text = no1 & Big

ElseIf no2>no1 Then

lblAns.Text = no2 &Big

ElselblAns.Text = Both Equal

End If

Use with Logical Operators

If no110 Then

lblAns.Text = Its Ok

ElselblAns.Text =Not Good

End If


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When we are comparing the same expression with

several values , then we can use Select....Case

statement as and alternative of If...Then...Else

We can use the To keyword for range of values We can also use Iskeyword for specific comparision

SelectCaseexpression

Case expression-n

LogicCaseElse

Logic

EndSelect


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Looping structure are used when a group ofstatements is to be executed repeatedly untila condition become True or False

VB.Net supports the follwoing loopstructures

For Next

Do Loop

While End While

For each Next


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The For loop executes a block of statements aspecific number of time

Remember that Next keyword should be used

in For....Next at the end.

Forcounter = start Toend [Stepincrement/decrement]Logic

Next


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Dim I as Integer

For I=0 To 10 Step 1

Logic...

NextDim I as Integer

For I=0 To 10Logic...

Next

Dim I as Integer

For I=50 To 1 Step -2

Logic...

Next

Dim I,J,K as Integer

For I=1 To 50

For J=1 To 30

For K=1 To 10

Logic...

Next Next Next

Dim I,J as Integer

For I=1 To 50

For J=1 To 30

Logic...

Next J,I

Dim I as IntegerFor I=1 To 100 Step 2

Next


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While loop keeps executing until thecondition against which it tests remain true.

The While statement always checks thecondition before it begins the loop.

In While loop programmer have to maintainor keep track of increment or decrement

value.Whilecondition

Logic

EndWhile

Dim no As Integer=5

While no>0

MsgBox(no)

no=no-1

End While


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Repeats a block of statments while a Booleancondition is False or until the conditionbecomes True.

We can use either While or Until. While: Repeat loop until condition is False. Until: Repeat the loop until condition is True.

Do{While| Until} condition

Logic.........

Loop

Do

Logic.........

Loop{While| Until} condition


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Dim ctl As new ControlDim cnt As Integer

For Each ctl Inme.Controls

If TypeOfctl Is TextBox Then

cnt = cnt +1

End If

Next

MsgBox(cnt)

TypeOf....Is Operator:

This operator is chechked first parameter withsecond type that whether given object is and

object of Is a given class.


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This is not a type of Loop Executes a series of statements making

repeated reference to a single object. The use of it do not require calling a name of

object again and again. To make this type of code more efficient and

easier to read, we use this blockWithobjectName

Logic

EndWith


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// Setting up properties of my button by using codeWith btnAns

.Text = Click Me

.ForeColor = Color.Green

.BackColor = Color.White

.Height= 50

.Width=100

End With


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A procedure is a set of one or more program statements that can

be run or call by referring to the procedure name.

Divide the big program into small procedures

An application is easier to debug and easy to find error.

Reusability of code. Two types of procedures are In-builtor User- defined procedure.

VB.Net have following type of procedures

Sub proceduresdoes not return value.

Event-handling procedures are sub procedure that execute inresponse to an event is triggered(Button1_Click)

Function procedures return a value

Property proceduresused in object oriented concept


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Public Class SubProdedure

Private Sub Button1_Click(ByVal sender As System.Object,

ByVal e As System.EventArgs) Handles Button1.Click

Hi(12, 15) // call Hi(12,15)

Sub Hi(ByVal a As Integer, ByVal b As Integer)

MsgBox("Hello I am Here " & "" + (a + b).ToString)

End Sub

End Class


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A Function procedure is similar to a subprocedure, but it return a value to the callingprogram.

Function may or may not have argument By Val is by default argument type As clause is written after the parameter list is

set. It return a value so call function using:

varname= functionName(argument)

By default function are public


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[Modifiers] FunctionFunctionName [(ParameterList)]

AsReturnType

Statements

Return Values]

End Function

Function add(ByVal s1 As Integer, ByVal s2 As Integer)

As Integer

Return s1 + s2

End Function


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We can specify procedure argument as an optionallike in C++ (default argument)

Its not compulsory to pass for calling it

It should be indicate by Optional keyword with

default value other wise it overwritten with defaultvalue.

Optional argument must be at last declareFunction add(ByVal s1 As Integer, Optional ByVal s2 As Integer =1)

As IntegerReturn s1 + s2

End Function

-----------------------------------------------------------------

Sub ad(ByVal s As Integer, Optional ByVal v As Integer = 1)

MsgBox(s + v)

End Sub


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There are two ways to pass arguments:

By Val (By Value) Default in VB.NET

By Ref (By Reference) By Val: refers to pass a copy of a variable to

procedure. We can make changes to the copyand the original will notbe altered. Variable

itself will not change with in the procedure By Ref: refers to actual argument(memory

address) itself is passed for the same variable

and arguments


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Sub Button ClickDim x,y As Integer

x= txt1.Texty= txt2.TextSwap(x,y)

txt3.Text = xtxt4.Text=y

End Sub

Sub Swap(By Val a As Integer,By Val b As Integer)Dim temp As Integer

temp=aa=bb=temp

End Sub


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3 ways to pass arguments

Passing Args. by Position(Ordered)

Passing Args. by Name (Use varname and :) Mixing Args. by Position and by Name


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FO is the implementation of Polymorphismconcept of the OOP.

In VB.Net we can declare two or moreprocedure with same name

When we declare more than one prodedurewith the same name but number argument

may be differing, types of arguments may bediffer or sequence of thoes argument may bediffer.


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Private Sub btn_Click()

add(...........)

End Sub

----------------

Sub add()

logic

End Sub------------------

Sub add(ByVal no As Integer)

logic

End Sub

------------------

Sub add(ByVal no1 As Integer, ByVal no2 As Integer)

logicEnd Sub

-----------------------

Sub add(ByVal no1 As Integer, ByVal no2 As Integer, ByVal no3 As

Integer)

logic

End Sub


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IIF

Returns one of two objects, depending on the

evalution of expression.

Its like Ternary operator in C or C++

IIF(Expression,Truepart,Falsepart)

Example

Dim salary As Integer =50000Dim strAns as String

strAns = IIF(salary>30000,Good,Bad)

MsgBox(StrAns)


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StrReverse(string)

Returns a string in which the character order of a

specified string is reversed

ASC(char)

Returns ASCII value for the input character

Chr(int)

Returns the character of that relative ASCII value


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Length() Compare() Concat() Copy() Equals() Trim() EndsWith() StartsWith() Indexof()

Ucase,Lcase,ToUpper,ToLower

Insert() PadLeft() PadRight() Remove() Replace() Substring()


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Objective of MsgBox is to produce a pop-upmessage box, prompt the user and returns aninteger indicating which button is clicked byuser

MsgBox and InputBox are inbuilt functions.MsgBox(Prompt,Button+Icon Style,Title)

MsgBoxis the Model dialog box MsgBox returns an integer value. The value is

determine by the type of buttons being

clicked by the user. (1-vbOk,2 vbCancel,3 vbAbort, 4 vbRetr ,5 vbI nore, 6 vbYes, 7 vbNo)


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Its an advance version of MsgBox function MessageBox is the class and show is method

of it Show method has more argument then

MsgBox function. It have special argumentfor icon and button

MessageBox.Show(Text,caption,button,icon,default button,options,helpbutton)


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InputBox function is to accept data from theuser.

An InputBox function will display a promptbox where the user can enter a value or amessage in the form of text.

The InputBox function with return a vlaue. We

need to declare the data type for values to beaccepted on the InputBox.

varName= InputBox(Prompt,Title,default_text,x-pos,

y-pos)


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11

2


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Create new project or Existing Project, Addnew form.

Set the property of mainform

Name= frmMDI or frmMain

Text= Main Form

IsMDIContainer=true

WindowState= Maximized (Set as StartUp form)


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What is Error ?

Error is somting that is unexpected.

Types of Error

Syntax (Design Time)

Runtime

Logical


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Exception Handling is an in-built mechanismin .NET to detect and handle run time errors.

Runtime errors are an expensive fact of lifeboth during development and after release asoftware to customers. Errors take time tofind and fix it

The .NET framework contains lots ofstandard exceptions. The exceptions are ariseduring the execution of a program. It can be

because of user, logic or system error.


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If programmer do not provide anymechanism to handle these error theprogram goes to terminates.

There are two way to trap Error

Structured Exception Handling (Newer)

Unstructured Exception Handling (Older)


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We use Try.......Catch......Finally statments. Catch and Finally blocks are optional All the exception are directly or indirectly

inherited from the ExceptionClass. We can Catch all the exception using

Catch ex As Exception block

Exceptionclass is the base class of all exceptionclass hirarchy. exobject of the class is used toaccess (error) the property of Exception class

You can use catch for multiple exception


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ex.ToString() will give the user a large

technical dump of the error that occurred likethe error description with path of the form inwhich error will arise, line of the error, eventname etc.

ex.Message() Will give a more to the

point error message. It display main moral ofthe error.


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In Button Click Event..........Try

Dim intNo1,intNo2 As Integer, ans As Integer

intNo1 = txtNo1.Text

intNo2 = txtNo2.Textans = intNo1+ intNo2

MsgBox(ans,Demo)

Catch ex As Exception

MsgBox(ex.ToString,Error1)MsgBox(ex.Message,Error2)

Finally

MsgBox(Hi i am at Finally part);

End Try


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OutOfMemory Exception NullReference Exception InvalidCast Exception

ArrayTypeMismatch Exception IndexOutOfRange Exception Arithmetic Exception

DivideByZeroException OverFlowException FileNotFoundException DirectoryNotFoundException


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UnStructured Exception are simple but now adays its obsolute in VB.NET programes

There are three way to handle error

On Error GoTo

On Error Resume Next

On Error GoTo 0 (Zero)


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Component Object Model is an interfacestandard for software component introducedby Microsoft in 1993. It is used to enable interprocess communication and dynamic objectcreation in any programming language thatsupports the technology. The term COM is

often used in the software developmentindustry as an umbrella term thatencompasses the OLE, OLE Automation,

ActiveX COM+ and DCOM technologies


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DCOM is Distributed Component ObjectModel.

It is the extension of the COM that allowsCOM components to communicate acrossthe network boundaries.

It can efficiently deploy and administrated

Its an open technology DCOM communications also work between

dissimilar computer hardware and OS


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COM DCOM

COM stands for Component objectmodel

Distributed component object model

COM is on local or on one single

machine

DCOM is a working across several

machinesCOM is used for Desktop Applications DCOM is used Network based

Applications

COM is collection of tools which areexecuted on client side environment

DCOM is a Distributed componentobject Model runs at the given server

COM Components exposes itsinterfaces at interface pointer whereclient access Components interface

DCOM is the protocol which enablesthe s/w components in differentmachine to communicate with eachother through n/w


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Managed Code is what Visual Basic .NET and C#compilers create.

The code, which is developed in .NETframework, is known as managed code. Thiscode is directly executed by CLR with help ofmanaged code execution. Any language that iswritten in .NET Framework is managed code.

Managed code uses CLR which in turns looksafter your applications by managing memory,handling security, allowing cross - language

debugging and so on


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The code, which is developed outside .NET,Framework is known as unmanaged code.

Applications that do not run under the

control of the CLR are said to be unmanaged,and certain languages such as C++ can beused to write such applications, which, for

example, access low - level functions of theoperating system. Background compatibilitywith code of VB, ASP and COM are examples

of unmanaged code


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Unmanaged code can be unmanaged sourcecode and unmanaged compile code.

Unmanaged code is executed with help of

wrapper classes. Wrapper classes are of two types: CCW (COM

Callable Wrapper)and RCW (Runtime

Callable Wrapper).


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unit 2 vb variables

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