Computing with c sharp and the net framework 2003

ComputingwithC#and
the.NETFramework
ISBN:0763723398
byArt
Gittleman
JonesandBartlettPublishers
©2003(753pages)

Bothnoviceandexperienced
programmerswillfindthat
thistextservesasan
accessibleandthorough
guidetoobject-orientedand
event-drivenprogramming
conceptsthroughthe
author'sspiralteaching
approach.
CDContent
TableofContents
ComputingwithC#andthe.NET
Framework
Preface
AnIntroductionto
Chapter1 ComputingwithC#
Chapter2 - C#ProgrammingBasics
SoftwareEngineering
Chapter3 withControlStructures
MoreControlStructures
Chapter4 andTypes
GettingStartedwith
Chapter5 - Object-Oriented

Programming
Chapter6 - WorkingwithObjects
Chapter7 - Arrays
Event-Driven
Chapter8 Programming
Chapter9 - UserInterfaces
Chapter10 - Inheritance
ExceptionHandlingand
Chapter11 Input/Output
Chapter12 - DataStructures
Chapter13 - ThreadsandAnimation
Chapter14 - Networking
Chapter15 - UsingaDatabase
Chapter16 - ASP.NET
Chapter17 - XMLandWebServices
BinaryandHexadecimal
AppendixA Numbers
BitwiseandShift
AppendixB Operators
OperatorPrecedence
AppendixC Table
AppendixD - TheASCIICharacterSet
AppendixE - SimpleTypes
AnswerstoSelectedExercises
Index
ListofFigures
ListofCodeExamples
CDContent

BackCover
ComputingwithC#demystifiestheartof
programmingwithC#throughclearexplanationsand
intuitiveexamples.Bothnoviceandexperienced
programmerswillfindthatthistextservesasan
accessibleandthoroughguidetoobject-orientedand
event-drivenprogrammingconcepts.Readersdevelop
amasteryofobjectsthroughtheauthor’sspiral
teachingapproach:firststraightforwardexamplesare
presented,thensimpleclassdesign,andfinallythe
moredifficultaspectsofinheritanceand
polymorphism.Theauthorapplieshisspiralteaching
approachthroughoutthetext,andreadersacquirea
meaningfulunderstandingofprogrammingconcepts
andtechniques.Thistextsetsthestandardfortoday’s
C#programmingbooks;readersofalllevelswill
benefitfromtherichlearningexperiencethatthistext
provides.
DistinctiveFeatures:
200complete,fullyannotatedprogramsare
includedtoprovideconceptswithaconcrete
embodimentthatfacilitateslearning.
Inadditiontobasicprogrammingconcepts,this
textintroducesdatastructures,threads,
networking,databaseaccess,XML,Web
programming,andWebservices.
Readerscanpracticetheirskillsthroughthe
followingexercises:TestYourUnderstanding,Skill

Builder,CriticalThinking,Debugging,Program


Modification,ProgramDesign,andmore!


ComputingwithC#andthe.NETFramework
ArtGittleman
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Copyright©2003byArtGittleman
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Allrightsreserved.Nopartofthematerialprotectedbythiscopyright
maybereproducedorutilizedinanyform,electronicormechanical,
includingphotocopying,recording,orbyanyinformationstorageand
retrievalsystem,withoutwrittenpermissionfromthecopyrightowner.
LibraryofCongressCataloging-in-PublicationData
Gittleman,Art.
ComputingwithC#andthe.NETframework/ArthurGittleman.
p.cm.
ISBN0-7637-2339-8
1.C#(Computerprogramlanguage)2.Microsoft.NETFramework.I.
Title.
QA76.73.C154G582003
005.13'3-dc212002040703
Editor-in-Chief,College:J.MichaelStranz
ProductionManager:AmyRose
AssociateEditor:TheresaDiDonato
AssociateProductionEditor:KarenC.Ferreira


SeniorMarketingManager:NathanJ.Schultz
ProductionAssistant:JennyL.McIsaac
CoverDesign:KristinE.Ohlin
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printedon45#HighlandPlus.
070605040310987654321
ToCharlottewithlove


Preface
C#andthe.NETFrameworksupportanew,integrated,powerfulInternet
programmingmodel.WenolongerneedtouseVisualBasicforrapid
applicationdevelopmentandforms,C++forobject-orientedapplications,
andASPfortheWeb.WecanuseC#forall,andwiththe.NET
Frameworkwehaveaplatformwithahugelibrarythatcanintegrate
applicationsacrosstheInternet.
ThistextteachesC#fromthebeginning,butincludesenoughmaterialfor
atwo-termcoursecoveringmoreadvancedtopics.Itteachesthe
conceptsofcomputingnecessaryforaCS-1course,butallowsthose
withpriorexperienceprogramminginanotherlanguagetoproceed
quicklyovertheearlierchapterstolearntheexcitingC#languageand
.NETFrameworkindepth.
CoretopicsincludeC#basics,controlstructures,types,object-oriented
programming,andarrays.Nextcomeevent-drivenprogramming,user
interfaces,andinheritance.Additionaltopicsincludeexceptionhandling,
files,datastructures,threads,animation,networking,databases,web
programmingwithASP.NET,andXMLandwebservices.Thelater
chapterscan,forthemostpart,bestudiedindependently,soan
instructorhasflexibilityinthechoiceoftopicsforamoreadvanced
course.
Ibelieveonelearnsbestfromexample,and,therefore,eachchapterhas
manycompleteprograms.Asprogrammerswelearntoaddcommentsto
ourcode,butforpedagogicalpurposeswherecommentswouldbeso
detailedastoclutterthecode,Iprefertousenotes.Eachnotecontainsa

longerexplanationofakeylineofcode,andappearsjustafterthecode,
allowingeasierreadingofthecodeitself.Byusingnotesinthisway,I
alsoavoidclutteringthetextwithdetailedcodeexplanationsandcan
focusonexplainingconcepts.
Onealsolearnsbydoing.TofacilitatelearningIincludemanyvaried
exercises.TestYourUnderstandingExercisesattheendofeachsection
givereadersachancetoassimilatethematerialimmediately.Answersto
theodd-numberedexercisesappearattheendofthetext,andanswers


totheeven-numberedexercisesareavailablewithcodeforallprogram
examplesonaStudentResourceCDincludedwiththetext.ThisCDalso
includesthe.NETframeworkSDK.
IincludeSkillBuilderandCriticalThinkingexercisesattheendofmost
chapterstoallowreaderstomasternewconcepts.Answerstothese
appearattheendofthebook.Adebuggingexerciseattheendofmost
chaptershelpsdevelopthisnecessaryskill.
ProgramModificationexercisesallowreaderstotacklethiscommontask.
ProgramDesignexercisesprovidepracticeincludingtheentire
developmentprocess.
Onecandebateendlesslythebestwaytointroduceobjects.Iliketo
presentobjectsearly,butusingaspiralapproachsostudentsbuilda
soundfoundationbeforedelvingintothedetails.ThusIstartwithan
intuitiveexampleinChapter5andcontinuetoshow,usingUML,howto
designaclassandcodeitinC#.IdefersomeconceptstoChapter6,and
themoredifficultinheritanceconceptstoChapter9.
Ithankreviewers
GeraldBaumgartner,TheOhioStateUniversity
DavidBinkley,LoyolaCollege
CorinneHoisington,CentralVirginiaCommunityCollege

KenrickMock,UniversityofAlaskaAnchorage
fortheirmanyperceptivecommentsandsuggestionsthatdidmuchto
improvethemanuscript.Ithasbeeagreatpleasureworkingwiththevery
helpfulandamiableCSteamatJonesandBartlett,includingMichael
Stranz,TheresaDiDonato,AmyRose,JennyMcIsaac,andKaren
Ferreira.
Thewebsiteforthisbookis
/>

IwillposterrataassoonasIbecomeawareofthem.Pleaseemailany
correctionstomeat



Chapter1:AnIntroductiontoComputingwith
C#
DownloadCDContent


Overview
Onceuponatime,giantdigitalcomputersfilledlargeroomswiththeir
thousandsofvacuumtubes.Theywereslowbeasts,butlooked
awesome.Intheyearssinceelectronicdigitalcomputerswerefirst
developedinthe1940s,computershavedramaticallydecreasedinsize
andincreasedincomputingpower.Startingasatoolforscienceand
engineering,computershavebecomeanessentialpartofoursociety.
Studyingcomputingchallengesustokeepupwithrapidtechnological
change.WithC#(pronouncedCsharp)wecanlearnthebasic
techniquesofprogrammingthathavebroughtustothispoint,andgo
forwardwithobject-oriented,interactive,graphical,event-driven

programming,networking,andwebservicesthattakeustothefuture.

Objectives
Introducebasiccomputingconcepts
SurveyC#history,itsfeatures,andhowitworks
IntroducetheelementsofaC#program
Introducetheprogramdevelopmentprocess


1.1IntroductiontoComputing
Hardware
Acomputerhasseveralbasiccomponents(seeFigure1.1).The
processorexecutesprogramsstoredinmemory,usingthememoryto
storedataneededincomputations.Externalstorage,includingdisk
drives,holdsprogramsanddata.Inputdevicessuchasakeyboardanda
mouseallowuserinteraction.Outputdevicesdisplayresults.Changing
technologyimprovestheperformanceofthesecomponentsandprovides
newtypes,butcurrentcommercialcomputershavethisorganization.


Figure1.1:Acomputersystem

Software
Softwareconsistsoftheprogramsthecomputerexecutes.Theoperating
systemsoftwaremakesitmucheasierforustousethecomputer.It
providesaninterfacetothehardwareforus,sothateachofusdoesnot
havetowriteprogramstoreadinputfromthekeyboard,writeoutputto
thescreen,orcreatefilesontheharddisk.Anoperatingsystemcanbe
relativelysimple,providingfewservices,oritcanbeahugeprogramwith
manybellsandwhistlesforustouse.

Programmersappreciateutilityprogramssuchaseditorsthatallowusto
createormodifyprogramsandcompilersthattranslateprogramsfrom
onelanguagetoanothertofacilitatetheirexecution.Endusersrunword
processors,spreadsheets,games,browsers,andmanyother
applications.Businessesrelyoncomputersoftwaretoservecustomers
andforthebusinesses'accounting,payroll,andothermanagement
needs.


Theprocessorexecutessoftwareusingitsspeciallydesignedinstruction
set.Eachinstructionissimplesothatitmaytakehundreds,thousands,
ormillionsofinstructionstoimplementthetaskswewantoursoftwareto
perform.Eachinstructionhasseveralparts.Thesepartsspecifythe
operation(addition,forexample)thattheinstructionperforms,andany
operandsthatituses,suchasthenumberstoadd.Eachmemory
locationhasanumericaladdress.High-levellanguagessuchasC#
provideinstructionstoperformtheequivalentofmanylow-levelmachine
instructions.

High-LevelLanguages
Eachprocessorhasitsowninstructionsetthatusesnumericalcodesfor
theoperatorsandnumericaladdressesfortheoperations.Each
instructionperformsonebasicstepsuchasanaddition,aload,ora
store.Programmingusingaprocessor'sinstructionsetwouldmakeit
difficulttoaccomplishanybutthesimplesttasks.Moreover,wewould
havetowritesuchaprogramalloveragainfortheinstructionsetofa
differentprocessor.AprogramusingprocessorABC'sinstructionsetwill
notrunonprocessorXYZ,andviceversa.
Ahigh-levellanguageallowsustoexpressthecomputationinamore
understandableform,combiningseveralstepsintooneexpression,and

towriteaprogramthatwecanimplementonmanytypesofprocessors.
Forexample,wecanexpressanadditionas
totalSalary=baseSalary+bonus;


Figure1.2:Translatingahigh-levelprogram
andwritemorecomplicatedstatementssuchas
totalScore=
(judge1Score+judge2Score+judge3Score)*difficulty;
whichrepresentsthetotalscoreobtainedbyfirstaddingthescoresof


threejudges,andthenmultiplyingthatsumbyadifficultyfactor.Weuse
theasterisk,*,todenotemultiplication.

Compilers
Acompilertranslatesaprogramfromonelanguagetoanother.Ifwewant
towriteaprograminahigh-levellanguageandrunitonprocessorABC,
wecanuseacompilertotranslateourhigh-levelprogramtoan
equivalentprogramusingtheinstructionsetofprocessorABC.Each
high-levelstatementwillusuallytranslatetoseveralprocessorABC
instructions.Figure1.2showsthisprocess.
TorunthesameprogramonprocessorXYZwewouldneedanother
compilerthattranslatesfromthehigh-levellanguagetotheinstructionset
ofprocessorXYZ.Thehigh-levelprogramiscalledthesourcecode,and
thetranslatedprogramiscalledtheexecutablecodeorthebinarycode
(reflectingitsuseofthebinarynumbersystemtorepresentoperatorsand
operands.)ImplementationsoftheCandC++languagesusuallyuse
compilerstoproduceexecutablecodeforspecificprocessors.
Compilersareindispensabletoolsforprogramdevelopers,butendusers

havenodesiretousethem.Aplayerofagamewantsaprogramthatwill
run—anexecutableprogram.Thevendorofthatgamemustprovide
executableversionsofthegameforeachprocessor.

Interpreters
Aninterpreterisaprogramthatexecutesthecoderatherthantranslating
ittoanotherlanguage.Forexample,aninterpreterwouldexecutethe
statement
totalSalary=baseSalary+bonus;
byfindingthevaluesofbaseSalaryandbonus,addingthem,and
storingtheresultintotalSalary.Inthisexample,theinterpreter
executesahigh-levellanguagestatement.TheBASIClanguage,usedon
earlypersonalcomputersthathadinsufficientmemorytosupportthe
compilationprocess,wastypicallyimplementedbyaninterpreter.


Wecouldalsouseaninterpretertoallowonemachinetosimulatethe
instructionsofanother,asshowninFigure1.3.Forexample,wecould
writeaprogramthatexecutes,onprocessorXYZ,programswrittenusing
processorABC'sinstructionset.ManyJavaimplementationsusea
combinationofcompilationandinterpretation,asdidthefirst
implementationsofthePascallanguage.


Figure1.3:Aninterpreterexecutingeachhigh-level
statement

Networks
Thusfarwehavefocusedonthesoftwareandhardwareforasingle
computer.WiththeadventoftheInternet,computerseasilycommunicate

withothercomputersinthesameoffice,thesamecompany,oratremote
sitesallovertheworld.Manyofususeemailmorethanweuseregular
mailorthetelephone.Acomputermaybeconnectedbycabletoother
computersinanetwork,oruseamodemtoconnectovertelephonelines.
TheInternetisavastnetworkofnetworksoverwhichweusefamiliar
servicessuchasemailandfiletransfer.TheWorldWideWeb,arapidly
growingpartoftheInternet,useshypertexttocreateaweboflinksfrom
onecomputertoanother.Hypertext,whichwediscusslaterinthetext,
allowsustoincludeimages,sounds,formattedtext,andlinkstoother
computersinwebpageswhichwedisplayusingabrowser.Manyuse
browsersoftwareastheirprimaryaccesstocomputers.Webservices
allowcomputerstocommunicatewithoneanother.
TheBIGPicture
Operatingsystemsoftwarehandlesthedetailsofinput,output,andfiles.
Eachhardwareprocessorusesitsownlow-levelinstructionset.Higher-


levellanguagesallowprogrammerstowritestatementsthataremore
meaningful.Acompilertranslatesaprograminahigh-levellanguageto
theinstructionsetforaspecificprocessor.Aninterpreterexecutesthe
high-levelcodedirectly.

TestYourUnderstanding
1. Describeeachcomponentofthecomputerthatyouwillbeusing
toprograminC#.Whatisthefunctionofeach?
2. Listseveralsoftwareapplicationsyouhaveusedorwouldliketo
use.Identifyeachasanoperatingsystem,wordprocessor,
game,etc.
3. Whatdowecallthetypeofprogramthattranslatesaprogram
inahigh-levellanguagetoanequivalentprograminanother

language?
4. Whatdowecallthetypeofprogramthatexecutesanother
program?
Answers
3. Acompiler.


1.2The.NETFramework
MicrosoftdevelopedtheC#languagealongwiththe.NETFramework,a
newcomputingplatformthatsimplifiesapplicationdevelopmentinthe
distributionenvironmentoftheInternet.Theydesignedthe.NET
Frameworktofulfillthefollowingobjectives[1]:
Toprovideaconsistentobject-orientedprogrammingenvironment
whetherobjectcodeisstoredandexecutedlocally,executed
locallybutInternet-distributed,orexecutedremotely.
Toprovideacode-executionenvironmentthatminimizessoftware
deploymentandversioningconflicts
Toprovideacode-executionenvironmentthatguaranteessafe
executionofcode,includingcodecreatedbyanunknownor
semitrustedthirdparty
Toprovideacode-executionenvironmentthateliminatesthe
performanceproblemsofscriptedorinterpretedenvironments
Tomakethedeveloperexperienceconsistentacrosswidely
varyingtypesofapplications,suchasWindows-based
applicationsandWeb-basedapplications
Tobuildallcommunicationonindustrystandardstoensurethat
codebasedonthe.NETFrameworkcanintegratewithanyother
code
The.NETFrameworkobjectivemeetstheneedsofprofessional
developers.Thistextpresentsonlyasmallpartofthe.NETFramework,

butwecannotclimbthemountainuntilwetakethefirststeps.
Thetwomainpartsofthe.NETFrameworkaretheCommonLanguage
Runtimeandthe.NETFrameworkclasslibrary.

TheCommonLanguageRuntime
TheCommonLanguageRuntime(CLR)managestheexecutionofcode


andprovidesservicesthatmaketheexecutionofcodeeasier."Runtime"
meansthatcodeisrunning,whichisanotherwayofsayingitisbeing
executed."CommonLanguage"meansthatthisruntimemanagesthe
executionofcodewritteninseverallanguagesthatsharetheservices
provided.
MicrosoftdevelopedC#totakeadvantageoftheCLR.Itsfeatureswork
especiallywellwiththeCLR.ThepopularVisualBasiclanguageevolved
toVisualBasic.NET,whichisanobject-orientedlanguagethattakes
advantageoftheCLR.VisualBasicprogrammershavetolearnmany
newfeaturestotakeadvantageoftheCLRusingVisualBasic.Net.C++,
likeitsCpredecessor,hasmanycapabilitiesthatdonotfitintothenew
approach.AversionofC++,calledmanagedC++,adaptsC++towork
withtheCLR,soC++programmerscanintegratecodewithotherCLR
users.
WecallcodethatusestheCLRmanagedcode.TheCommonType
Systemdefinesthetypesofdatathatmanagedcodecanuse.A
CommonLanguageSpecification(CLS)definesfeaturesthatevery
languagefordevelopingmanagedcodemustprovide.Programmerswho
useonlyfeaturesintheCommonLanguageSpecificationcanbuildan
applicationcombiningprogramsindifferentlanguages.Theywillknow
thatiftheyuseafeatureinonelanguage,aprograminanotherlanguage
willalsobeabletousethatsameconstruct.

Togiveasimplifiedexample,considernumbers.Supposewehavespace
foronly10numbers.Ifweuseonlynonnegativenumbers,wecanuse0,
1,2,3,4,5,6,7,8,and9.Ifweneedtoincludebothpositiveand
negativevalues,wewouldchoose–5,–4,–3,–2,–1,0,1,2,3,and4.
Theunsignedtypeallowsustouselargervalues,butthesignedtype
allowsustousenegativevalues.Inananalogoussituation,theCommon
TypeSystemprovidesbothunsignedandsignedtypes,butonlyrequires
thatlanguagesprovidesignedtypestosatisfytheCommonLanguage
Specification.
Adeveloperwhousesonlysignedtypescanexpecteverylanguagethat
followstheCLStointeroperatewiththecodeproduced.Adeveloperwho
usesunsignedtypesmayproducecodethatanotherlanguagethat


followstheCLSisnotrequiredtosupport.
Abigproblemfacingdevelopersisthemanydifferenttypesofprocessors
thatruncode.Windows,Macintosh,andUnixmachinesuseawide
varietyofhardware,asdopersonaldigitalassistants,cellphones,large
computers,andotherplatforms.Onewaytomakeaprogramworkon
eachofthesedevicesistotranslatetheprogramtothenativeinstruction
setforthatdevice.Saywehave10programminglanguagesand10
devices.Usingthisapproach,intheworstcase[2]wewouldneed100
compilerstotranslateprogramsineachofthe10languagestonative
codeforeachofthe10devices.Figure1.4diagramsthisjumbleof
compilers.


Figure1.4:Compilingthreelanguagestonativecodeforthree
machines
Anotherapproach,usedbytheCLR,istoprovideanintermediate

languagethatismuchlikethenativelanguagesofdevices.This
languageiscalledMSIL,MicrosoftIntermediateLanguage.Wecompile
eachlanguagetoMSIL.DuringruntimetheCLRusesaJIT(JustIn
Time)compilertocompiletheMSILcodetothenativecodeforthe
deviceused.[3]ThisrequiresoneJITcompilerforeachdeviceto
translateMSILcodetothenativecodeforthatdevice.Thistranslation
processisnotasdifficultastranslatingahigh-levellanguagetonative
code,becausetheMSILcodeissimilartonativecode.



Figure1.5:Compilingusinganintermediate
language
Moreover,usingMSILgreatlyreducesthenumberofcompilersweneed.
For10languagesand10devices,weneedonecompilerforeach
languagetotranslateittoMSIL,andoneJITcompilerforeachdeviceto
translateMSILcodetonativecodeforthatdevice.Thusweneed20
compilersinsteadof100.Figure1.5illustratesthisapproach.

The.NETFrameworkClassLibrary
The.NETFrameworkClassLibraryprovidesalargeandveryusefulset
oftypesthatexpeditethedevelopmentprocess.Thelibrarygroupsthe
typesinnamespacesthatcombinerelatedtypes.Itcontainsabout100
namespacesofwhichweuseonlyasmallnumberinthistext.Someof
thenamespacesfromthelibrarythatweuseare:
System
Containsfundamentaltypes
System.Collections
Definesvariouscollectionsofobjects
System.Data

Managesdatafrommultiplesourcesincludingdatabases
System.Drawing
Providesgraphics
System.IO
Allowsreadingandwriting
System.Net
Providesaninterfacecomputersusetocommunicateover


networks
System.Runtime.Remoting
Supportsdistributedapplications
System.Text
Handlescharacterencoding
System.Threading
Enablesmultithreadedprogramming
System.Web
Enablesbrowser–servercommunication
System.Web.Services
Enablesthebuildinganduseofwebservices
System.Windows.Forms
ForuserinterfacesinWindows-basedapplications
System.Xml
ProvidessupportforprocessingXML
TheBIGPicture
The.NETFrameworkhelpsdevelopersbuildapplicationsforthediverse
Internetenvironment.TheCommonLanguageRuntimeand.NET
FrameworkClassLibraryprovideservicesandtypestomake
programmersmoreproductive.

TestYourUnderstanding
5. WhatdowecallcodethattargetstheCommonLanguage
Runtime?
6. Whatarethetwomainpartsofthe.NETFramework?
Answers


5. managedcode
[1]"Overviewofthe.NETFramework,"fromthe.NETFramework
Developer'sGuide.See />[2]Moderncompilersusesimilartechniquestoreducethenumber
neededtosupportmultipleplatforms.
[3]JavaalsousesaJITcompiler.


1.3OverviewofC#
History
FORTRANandCOBOLwereamongthefirsthigh-levellanguages,
introducedinthelate1950s.Botharestillusedtoday,FORTRANfor
scientificapplicationsandCOBOLforbusiness.Smalltalk,released
around1980,isafullyobject-orientedlanguagethatinfluencedits
successors,includingJavaandC#.
Systemsprogrammerswhoneededaccesstothemachinehardware
usedassemblylanguages,whichareverylow-levelandspecifictothe
hardware.TheClanguage,developedinthemid1970s,issometimes
describedasaportableassemblylanguage.Itisahigh-levellanguage,
likeFORTRANandCOBOL,butprovidesaccesstomachinehardware.
TheUNIXoperatingsystem,developedforthethen-newminicomputers,
wasmostlywritteninC,andbothCandUNIXrapidlygrewinpopularity.
Althoughitisgoodforsystemsprogramming,Cisasmalllanguagethat
doesnotfacilitatethedevelopmentoflargesoftwaresystems.Introduced

inthelater1960s,object-orientedprogrammingstartedtobecome
popularinthemid1980s.Languagesthatsupportobject-oriented
programmingdofacilitatethedevelopmentoflargesoftwaresystems.
C++extendsCtoincludeconstructsthatsupportobject-oriented
programming,whilestillincludingthosethataccessmachinehardware.
Consequently,C++grewinpopularity.
BASICwasdevelopedinthe1960sasaneasierwayforstudentsto
learntoprogram.Itusedaninterpretersostudentscouldimmediately
seetheresultsofexecution.Originally,personalcomputershadvery
limitedmemorychipsinwhichtoholdprograms,soBASIC,whichdidnot
requirecompilationtoalargerlow-levelrepresentation,becamethemain
languageusedonearlyPCs.Asmemorybecamecheaperandgraphics
capabilitiesgrew,BASICmorphedtoVisualBasic,anextremelypopular
languagefortherapiddevelopmentofuserapplications.
Withtheintroductionofthe.NETFramework,VisualBasicevolvedto
VisualBasic.NET,acousinofC#.OnewaywemightdescribeC#isasa


languagethattriestocombinetherapidapplicationdevelopmentof
VisualBasicwithmuchofthepowerofC++.
WiththeriseofdesktopcomputersandtherapidgrowthoftheInternetin
themid1990scametheneedforalanguagetosupportprogrammingto
enableusersonvastlydifferentsystemstointeractinasecureway.
Java,introducedin1995,usesaJavaVirtualMachinetoprovidesecurity
andenableprogramsdevelopedondifferentsystemstointeract.Alarge
libraryextendsitscapabilitiesforInternetprogramming.Becauseitsuited
thenewdemandsondevelopers,Javahasbecomeverypopular.
ThegoalsofC#aresimilartothoseofJava.Thoseversedinoneof
theselanguagescanrapidlyconverttousingtheother.C#hadthe
advantageofseeingtheJavaapproachandhowitmightenhanceit.C#

addsfeaturesfortheeasydevelopmentofcomponentstomakeiteasier
fordeveloperstocombineprogramswrittenondifferentsystems.One
canannotateaC#programwithattributesthatbecomepartofthe
runtimeusedbytheCLR.Thismetadatadescribestheprogramsothat
otherprogramscanuseit.C#,newlydevelopedinthetwenty-first
century,promisestobecomeverypopularastheprimary.NET
programminglanguage.

C#Features
Microsoft[4]identifiesC#asamodernobject-orientedlanguagethat
allowsprogrammerstoquicklybuild.NETcomponentsfromhigh-level
businessobjectstosystem-levelapplications.Thesecomponentscan
easilybeconvertedtowebservicestobeusedovertheInternet.
Importantcharacteristicsare:
Productivityandsafety:C#usesthe.NETplatformsupporting
webtechnologies.C#workswellwithXML,theemerging
standardtopassstructureddataovertheInternet.
TheC#designeliminatesmanycostlyprogrammingerrors.It
includesautomaticmemorymanagementandinitializationof
variables.Itcheckstypestoavoidruntimeerrors.


C#reducesupdatingcostsbysupportingversioninginthe
language,makingiteasierandlesscostlytointroducenew
versionsofaproduct.
Power,expressiveness,andflexibility:C#allowsaclose
connectionbetweentheabstractbusinessprocessandits
softwareimplementation.Thedevelopercanassociatemetadata
withaprogramthatwillallowtoolstodeterminethatacomponent
iscorrectlyidentifiedaspartofabusinessobjectortocreate

reports.
ToavoidtheneedtouseC++toaccessbasicmachinefunctions,
C#permitscarefullyidentifiedlow-levelaccesstomachine
resources.

HowC#Works
C#usesacompiler,butdoesnotimmediatelytranslateahigh-level
programtothemachineinstructionsofeachspecificprocessor.TheC#
compilertakesasinputthehigh-levelC#programandoutputsan
equivalentprogramwrittenusingtheMicrosoftIntermediateLanguage.
DuringruntimetheCLRusesaJITcompilertotranslatetheMSILcodeto
theinstructionsetoftheprocessor.Figure1.6showsthecompilationofa
C#programtoMSILfollowedbytheJITcompilationtonativecodeon
twodifferentprocessors.


Figure1.6:CompilingaC#program
TheadvantageofproducingMSILcodeinsteadofcodeforeachdifferent
processoristhatthesameintermediatecodewillrunonanyprocessor
thathasaCLR.WecandownloadaC#programwhichhasbeen
compiledtointermediatecodeononetypeofmachineandrunitona