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F5227VISUALBASIC.NETPROGRAMMING

Topic3.0CommonProgrammingTechniques3.4 SubProceduresandFunction

Procedures

CourseLearningOutcome(CLO) Upon completion of this course, students should be able to :

1. Create a simpe VB.NET based application based on the

Windows Application template.

2. Describe on essential terminology including memory,

.

3. Apply object oriented programming techniques to

create classes, add methods and add properties.

4. create a simple VB.NET based Web forms application

that uses an XML Web Service and manipulate data in

database by using Microsoft ADO.NET.

Procedures Procedure aunitofcodethatexecuteswhencalledfrom

anotherplace.

NotanewfaceSubproceduredefinition abuttonclickevent

PrivateSub btnDisplay_Click(ByVal senderAsSystem.Object,

ByValeAsSystem.EventArgs) HandlesbtnDisplay.Click

.EndSub

Or:

lstOutput.Items.Clear() subprocedurecall

proceduredefinition Defineswhat toexecutewhentheprocedureiscalled.

procedurecall Defineswhen toexecutetheprocedure.3

Procedures Aproceduremusthaveanamefollowingby().

E.g.

lstOutput.Items. Clear()

lstOutput.Items. Add(******)

CDbl(txtInputOne.Text)

Purposeofusingprocedures makeyourcodewellorganizedandeasytounderstand.

4

ProceduresWithout Using Procedures:Button click event:

Create variablesTake two user inputs, and

store them to variablesPerform the addition and

display the result

Perform the subtraction andi l l

Using Procedures:Create variablesButton click event:

Take two user inputs, andstore them to variables

Add()Subtract()

Multiply()i iisplay e resulPerform the multiplication

and display the resultPerform the division and

display the result (handle

divide by 0 situation here)End of event

ivi eEnd of eventDefine Add():

Perform the addition anddisplay the result

Define Subtract():Perform the subtraction and

display the resultDefine Divide()

Perform the division anddisplay the result(handledivide by 0 situation here)

Cont.

TherearetwotypesofproceduresinVisualBasic.NET:

9Subprocedures

Funct onsproce ures

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Subprocedure

ASubprocedureisablockofcodethatis

executedin

response

to

an

event

that

you

can

callwithparameterswhichdoesntreturna

.

BybreakingthecodeinamoduleintoSubprocedures,itbecomesmucheasiertofindor

modifythecodeinyourapplication.

Cont.

Subproceduresare methods whichdonotreturnavalue.

EachtimewhentheSubprocedureiscalledthestatementswithinitareexecuteduntilthe

matchingEndSubisencountered.

SubMain(), thestartingpointoftheprogramitselfisasubprocedure.

SubProcedures Sub procedure executeablockofcodeswhencalled

DefineaSubprocedure:

Private Sub name()

actionshere

ThekeywordPrivate meansthisSubcanonlybeusedbythisForm.

TheSubprocedurecallmustmatchwiththeSubproceduredefinition.

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SubProcedures E.g.auserdefinedSubdefinitionandSubcall

PrivateSubbtnCompute_Click(ByVal senderAsSystem.Object,ByVal eAs

System.EventArgs) HandlesbtnDisplay.Click

intFirst =CInt(nudFirst.Value)

intSecond =CInt(nudSecond.Value)

Add()Subcall.TheprogramwilllookforaSubdefinitionwiththesamenameto ec ew atto o

EndSub

SubdefinitionPrivateSubAdd()

DimintResult AsInteger=0

intFirstand intSecondareglobalvariables,sotheycanusedbybothSubs.intResult=intFirst +intSecond

txtAddResult.Text =CStr(intResult)

EndSub

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SubMain(bytradition)isasubprocedurethatisthefirstsubtobeexecuted,itiswherethe

programstarts.

Whenthe

application

starts

execution, control

istransferredtoMainSubprocedure

automaticallywhichiscalledbydefault.

SubProcedures

Subprocedurescanhavedifferentformalparameters,andtheseformalparameterscan

beseparatedwithlinecontinuationsfora

more

readable

source

text. Itcantakearguments,suchasconstants,

variables,orexpressions,thatarepassedtoit

bythecallingcode.

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Syntax

[Private|Public][Static]Sub

procedurename (arguments)statementsEndSub

Example:

PrivateSubMain()

Console.WriteLine("Hello there!")

Console.WriteLine("PressEntertocontinue...")

Console.ReadLine()

EndSub

CallingaSubProcedure

Onceyouhaveaprocedure,whetheryou

createdit

or

it

is

part

of

VBasic,

you

can

use

it.

Usingaprocedureisalsoreferredtoascalling

.

Beforecallingaprocedure,youshouldfirstlocatethesectionofcodeinwhichyouwant

touseit.

Tocallasimpleprocedure,typeitsnamefollowedbyparenthesesinthesectionwhere

youwanttouse.

ExampleCodeProgram1

ModuleModule1

SubMain()

System.Console.WriteLine("HellofromVisualBasic")

EndModule

CodeProgram2

ModuleModule1

SubMain()

DisplayMessage()

n u

SubDisplayMessage()

System.Console.WriteLine("HellofromVisual

Basic")

EndSub

EndModule

FunctionProcedures

Functionisamethodwhichreturnsavalue.

Functionsareusedtoevaluatedata,makecalculationsortotransformdata.

Declarin

aFunction

is

similar

to

declarin

a

Subprocedure.

FunctionsaredeclaredwiththeFunctionkeyword

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Example

ModuleModule1

SubMain()

EndSub

,

Integer)AsLong

Returnint1+int2

EndFunction

EndModule

Explaination

Returnavaluefromafunctionwiththe

Return statement Theprogramreturningthesumofthetwo

.

Whencallafunctionbyusingitsnameandan

argumentlistenclosedinparentheses,that

nameisreplacedbythevaluereturnedbythe

function

Example

ModuleModule1

SubMain()

DimintValueAsInteger=2

System.Console.WriteLine("{0}+{1}={2}",_intValue,

nt a ue, em nt a ue, nt a ue

EndSub

FunctionAddem(ByValint1AsInteger,ByValint2AsInteger)

AsLong

Returnint1+int2

EndFunction

EndModule

PassingParameters

Parameterscanbepassedtoaprocedureinoneoftwoways.

Eitherbyreference(ByRef)orbyvalue(ByVal).

When ouusetheb re erence methodchangesmadetoparameters'valuesinasub

procedureareknownwhencontrolreturns

backtothecallingprocedure

ByRefisthedefaultmethodofparameterpassinginVB6andpriorversionswhenthe

parameter'sdatatypeisanintrinsiconesuch

as

Integer,

Long,

Boolean,

String,

etc

ByVal

Thensecondmethodispassbyvalue(ByVal).

Thisisthedefaultforallnonintrinsicdatatypes.

W enpasse yva ue,t eca ngproce ureknowsnothingaboutchangesmadetothe

parameter'svalueinasubprocedure.

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VB.NETpassesallparametersByVal.

Thus,don'trelyonthedefaultbehaviorand

alwaysexplicitly

specify

ByVal or

ByRef in

your

parameterlists.

AModuleforVB.NETisafile(endingin.vb)thatcontainsprogramcodeandsub

proceduresto

execute.

Youmayalsoincludemodulesintoother

projectstocallon.

Accessibility

TheaccessibilitycanbePublic,Protected,Friend,ProtectedFriend,orPrivate.

YoucandefineSub proceduresinmodules,, .

TheyarePublic bydefault,whichmeansyou

cancallthemfromanywhereinyour

application.

Syntax

[accessibility]Subsubname[(argumentlist)]

'StatementsoftheSubproceduregohere.

EndSub

Example:

PrivateSubDisplayMessage(ByValstrTextAsString)

ArgumentDeclaration Youdeclareeachargumentforaprocedure

thesamewayyoudeclareavariable,

specifyingtheargumentnameanddatatype.

,

andwhethertheargumentisoptional.

ArgumentSyntax

[Optional][ByVal|ByRef] [ParamArray] argumentnameAsdatatype

Iftheargumentisoptional,youmustalsosupplyadefaultvalueinits

declaration,asfollows:

CopyOptional[ByVal|ByRef] argumentnameAsdatatype=defaultvalue

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LocalVariablesandGlobalVariables

LocalVariables:

Purpose: foraspecificproceduretouse

Scope:onlyusedinsidethatprocedure

Where:createdinsideaprocedure

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GlobalVariables:

Purpose:avariablesharedbydifferentprocedures

Scope:theform,alsocalledformvariables,canbeusedanywhereinthesameform

Where:createdatthebeginningoftheClass,outsideofanyprocedures

LocalVariablesandGlobalVariables

Local Variables:Add Button click event procedure:

3 local variables, only used

inside this procedure

Create variables 1, 2, and 3Take user input and store invariable 1 and 2

Add variable 1 to variable 2l

Global Variables:Create 2 global variables outside of

any procedure, can be used anywhere

Create variables 1, 2Add Button click event procedure:

Add()End of event procedureProcedure Add():

1local variable onl usedlvariable 3

End of event procedure

,

inside this procedure

Create variable 3use global variable 1 and 2

Take the user input and storein variable 1 and 2

use global variable 1 and 2, andlocal variable 3

Add variable 1 to variable 2and store the result tovariable 3

End of Add procedure

Conclusion

ASub procedureisaseriesofVisualBasic

statementsenclosedbytheSub andEndSubstatements.

Eachtimetheprocedureiscalled,its

statementsareexecuted,startingwiththefirst

executablestatementaftertheSub statement

andendingwiththefirstEndSub,ExitSub,orReturnstatementencountered.