C++面向对象程序设计双语教程（第3版）课件全套 ch01Introduction-ch08Templates

IntroductionC++面向对象程序设计双语教程(第3版)Chapter101OverviewofProgrammingWhatIsProgramming?Muchofhumanbehaviorandthoughtischaracterizedbylogicalsequences.Sinceinfancy

youhavebeenlearninghowtobehaveandhowtoperformtasks.Andyouhavelearnedto

expectcertainbehaviorfromotherpeople.OverviewofProgrammingOnthebroadscale,mathematicscouldneverhavebeendevelopedwithoutlogically

sequencedstepsforsolvingproblemsandprovingtheorems.Massproductionwouldnever

haveworkedwithoutoperationstakingplaceinacertainorder.Ourwholecivilizationisbased

ontheorderofthingsandactions.Wecreateorder,bothconsciouslyandunconsciously,throughaprocessthatwecallprogramming.OverviewofProgrammingProgrammingProgrammingisplanninghowtosolveaproblem.Nomatterwhatmethodisusedthe

pencilandpaper,sliderule,addingamachine,orcomputer-problemsolvingrequiresprogramming.Ofcours,howoneprogramdependsonthedeviceoneusesinproblem-solving.OverviewofProgrammingProgramamingisplanningtheperformanceofataskoranevent.Computerprogrammingistheprocessofplanningasequenceofstepsforacomputertofollow.Computerprogramisasequenceofinstructionstobeperformedbyacomputer.OverviewofProgrammingTowriteasequenceofinstructionsforacomputertofollow,wemustgothrougha

three-phaseprocess:problem-solving,implementation,andmaintenance(seeFigure1-1).OverviewofProgrammingUnderstand(define)theproblemandwhatthesolution

mustdo.Analysisandspecification.Developalogicalsequenceofstepsthatsolvesthe

problem.Generalsolution(algorithm).Followthestepsexactlytoseeifthesolutiondoessolvetheproblem.Verify.OverviewofProgrammingAnalgorithmisaverbalorwrittendescriptionofalogicalsequenceofactions(orevents).Afterdevelopingageneralsolution,theprogrammerteststhealgorithm,walkingthrougheach

stepmentallyormanually.Ifthealgorithmdoesnotwork,theprogrammerrepeatsthe

problem-solvingprocess,analyzestheproblemagainandcomesupwithanotheralgorithm.OverviewofProgrammingWhentheprogrammerissatisfiedwiththealgorithm,he/shetranslatesitintoa

programminglanguage.Althoughaprogramminglanguageissimpleinform,itisnotalwayseasytouse.Programmingforcesyoutowriteverysimple,exactinstruction.Translatinganalgorithmintoaprogramminglanguageiscalledcodingthealgorithm.OverviewofProgrammingOnceaprogramhasbeenputintouse,itisoftennecessarytomodifyit.Modificationmay

involvefixinganerrorthatisdiscoveredduringtheuseoftheprogramorchangingthe

programinresponsetochangesintheuser'srequirements.Eachtimetheprogramismodified,itisnecessarytorepeattheproblem-solvingandimplementationphasesforthemodified

aspectsoftheprogram.OverviewofProgrammingThisphaseoftheprogrammingprocessisknownasmaintenanceandactuallyaccountsforthemajorityoftheeffortexpendedonmostprograma.Inaword,theproblem-solving,implementationandmaintenancephasesconstitutetheprogramslifecycle.OverviewofProgramming02ProgrammingMethodologiesProgrammingmethodologydealswiththeanalysis,designandimplementationof

programs.Therearemanyformsofprogrammingmethodology.Thepurposeofmaking

explicitawarenessofprogrammingmethodologyistoallowtheprogrammertobeawareof

theprocessesandprocedureswhichtheyusewhenconstructingprograms.ProgrammingMethodologiesDataAbstractionOneofthekeystosuccessfulprogrammingistheconceptofabstraction.Abstractionis

crucialtobuildingthecomplexsoftwaresystems,Agooddefinitionofabstractioncomesfrom

andcanbesummedupasconcentratingontheaspectsrelevanttotheproblemandignoring

thosethatarenotimportantatthemoment.ProgrammingMethodologiesThepsychologicalnotionofabstractionallowsonetoconcentrateonaproblemata

certainlevelofgeneralizationregardlessoftheirrelevantlow-leveldetails;useofabstraction

alsoallowsonetoworkinanenvironmentwithfamiliarconceptsandtermswithouttheneed

totransformittoanunfamiliarstructure.ProgrammingMethodologiesStructuredProgrammingDividingaproblemintosmallersub-problemsiscalledstructureddesign.Eachsub-problemisthenanalyzedandasolutionisobtainedtosolvethesub-problem.The

solutionstoallsub-problemsarecombinedtosolvetheoverallproblem,Thisprocessof

implementingastructureddesigniscalledstructuredprogramming.ProgrammingMethodologiesThestructured-design

approachisalsoknownasthetop-downdesign,stepwiserefinementandmodular

programming(seeFigure1-2).ProgrammingMethodologiesForusingstructuredprogramming,therearemanygoodreasons:codesareeasierto

understandanderrorsareeasiertofind.Anerrorwillalwaysbelocalizedtoasubroutineor

functionratherthanburiedsomewhereinamassofcode.Thescopeofvariablescanbe

controlledmoreeasily,Withthereuseofcodesaswellasbeingreusedwithinasingl

application,themodularprogrammingallowscodestobeusedinmultipleapplications.Thus.

programsareeasiertodesignthedesignerjustneedstothinkaboutthehigh-levelfunctions.ProgrammingMethodologiesCollaborativeprogrammingispossible--modularprogrammingenablesmorethanone

programmertoworkonasingleapplicationatthesametimewhilethecodescanbestored

acrossmultiplefiles.ProgrammingMethodologiesTheoutputisthesameasabove,butthistimethechanceofthescriptoperationbeing

alteredduetoatypingerrorisgreatlyreduced.Inaddition,ifthereisanerror,thetaskof

correctingitismademuchsimpler.Theprogrammercanalsousethefunctionalitythroughout

theirapplicationwithoutworryingabouthavingtorewritethecode,therebyimprovingthe

codeandthetimeefficiency.ProgrammingMethodologiesStructuredprogramnmingStructuredprogramnmingisaprogrammingparadigmthatenforcesalogicalstructureontheprogrambeingwrittentomakeitmoreelicientandeasiertounderstandandmodifyItisakindoftop-downdesign,stepwiserefinementandmodularprogramming.Itdividesaproblemintoseveralsub-problems,andeachsub-roblemisthenanalyzed,afterward.asolutionisobtainedtosolvethesub-problem.Thesolutionstoallsub-problemsarefnallycombinedtosolvetheoverallproblem.ProgrammingMethodologiesObject-OrientedProgramming(OOP)isawidelyusedprogrammingmethodology.InOOP,thefirststepistoidentifythecomponentscalledobjects,whichformthebasisofthesolution,andtodeterminehowtheseobjectsinteractwithoneanother,asshowninFigure1-3.Thenextstepistospecifyforeachobjecttherelevantdataandpossibleoperationstobeperformedonthedata.Object-OrientedProgrammingProgrammingMethodologiesFipure1-3Object-orientedprogramming.ProgrammingMethodologies03CharacteristicsofObject-OrientedProgrammingObject-orientedprogramming(OOP)isaprogrammingparadigmthatuses“objects”

datastructuresconsistingofdatafieldsandmethodstogetherwiththeirinteractions-to

designapplicationsandcomputerprograms.Programmingtechniquesmayincludefeaturessuchasdataabstraction,encapsulation,polymorphism,andinheritance.Itwasnotcommonly

usedinthemainstreamsoftwareapplicationdevelopmentuntiltheearly1990s.Manymodern

programminglanguagesnowsupportOOP.CharacteristicsofObject-OrientedProgrammingAclassAclassisauser-defineddatatypewhichcontainsvariables,propertiesandmethodsinit.Aclassdefinestheabstractcharacteristicsofathing(object),includingitscharacteristics(itsattributes,fieldsorproperties)andthething'sbehaviors(thethingsitcando,ormethods

operationsorfeatures).Onemightsaythataclassisablueprintorfactorythatdescribesthe

matureofsomething.CharacteristicsofObject-OrientedProgrammingMethodThemethodisasetofproceduralstatementsforachievingthedesiredresult.Itperforms

differentkindsofoperationsondifferentdatatypes.Inaprogramminglanguage,methods

sometimesreferredtoas“functions”)areverbs.Forexample,Lassie,beingaDogobject,has

theabilitytobark.CharacteristicsofObject-OrientedProgrammingMethodSobarkisoneofLassie'smethods.Shemayhaveothermethodsaswell

forexample,sitoreatorwalkorsave.Withintheprogram,usingamethodusuallyaffects

onlyoneparticularobject;alldogscanbark,butyouneedonlyoneparticulardogtodothe

barking.CharacteristicsofObject-OrientedProgrammingMessagepassingistheprocessbywhichanobjectsendsdatatoanotherobjectorasks

theotherobjecttoinvokeamethodwhichisknowntosomeprogramminglanguagesas

interfacing.Forexample,the22啊obiectcalledBreedermaytelltheLassieobjecttositbypassing

a“sit”messagewhichinvokes

Lassie's“sit”method.MessagePassingCharacteristicsofObject-OrientedProgrammingAbstractionisoneofthemostpowerfulandvitalfeaturesprovidedbyobject-oriented

programming.Theconceptofabstractionrelatestotheideaofhidingdatathatarenotneededforthepresentation.Themainideabehinddataabstractionistoclearlyseparatetheproperties

ofdatatypeandtheassociatedimplementationdetails.AbstractionCharacteristicsofObject-OrientedProgrammingEncapsulationEncapsulationconcealsthefunctionaldetailsofaclassfromobjectsthatsendmessages

toit.Forexample,theDogclasshasabarkmethod.Thecodeforthebarkmethoddefines

exactlyhowabarkhappens(e.g,byaninhalemethodandthenanexhalemethod,ata

particularpitchandvolume).Timmy,Lassie'sfiend,however,doesnotneedtoknowexactly

howshebarks.Encapsulationisachievedbyspecifyingwhichclassesmayusethemembersofanobject.CharacteristicsofObject-OrientedProgrammingInheritanceisaprocessinwhichaclassinheritsallthestateandbehaviorofanother

class.Thistypeofrelationshipiscalledchild-parentorisarelationship.“Subclasses”aremore

specializedversionsofaclass,whichinheritattributesandbehaviorsfromtheirparentclasses,andcanintroducetheirown.InheritanceCharacteristicsofObject-OrientedProgrammingForexample,theDogclassmighthavesub-classescalledCollie,Chihuahua,and

GoldenRetriever.Inthiscase,LassiewouldbeaninstanceoftheColliesubclass.Supposethe

DogclassdefinesamethodcalledbarkandapropertycalledfurColor.Eachofitssub-classes

(Collie,Chihuahua,andGoldenRetriever)willinheritthesemembers,meaningthatthe

programmeronlyneedstowritethecodeforthemonce.CharacteristicsofObject-OrientedProgramming04C++ProgrammingLanguage“Aslongastherewerenomachines,programmingwasnoproblematall;whenwehadafewweakcomputers,programmingbecameamildproblemandnowthatwehavegiganticcomputers,programminghasbecomeanequallygiganticproblem,Inthissensetheelectronicindustryhasnotsolvedasingleproblem,ithasonlycreatedthem-ithascreatedtheproblemofusingitsproduct”(E.WDijkstra,TuringAwardLecture,1972).C++ProgrammingLanguageHistoryofCandC++CevolvedfromtwopreviousprogramminglanguageBCPLandB.BCPLwasdevelopedin1967byMartinRichardsasalanguageforwritingoperatingsystemssoftwareandcompilers.KenThompsonmodeledmanyfeaturesinhislanguageBaftertheircounterpartsinBCPLandusedBtocreateearlyversionsoftheUNIXoperatingsystemattheBellLaboratoriesin1970onaDECPDP-7computer.C++ProgrammingLanguageHistoryofCandC++BothBCPLandBwere“typeless”anguage-everydataitemccupiedone“word”inmemorywhiletheburdenoftreatingadata

itemasawholenumberorarealnumber.forexample.fellontheshouldersofthe

programmer.C++ProgrammingLanguageThemostimportantthingtodowhenlearningC++istofocusonconceptsandnotgetlostinlanguage-technicaldetails.Thepurposeoflearningaprogramminglanguageistobecomeabetterprogrammer,thatis,tobecomemoreeffectiveatdesigningandimplementingnewsystemsandatmaintainingoldones.Forthis,theappreciationofprogramminganddesigntechniquesisfarmoreimportantthantheunderstandingofdetails,whichcomeswithtimeandpractice.LearningC++C++ProgrammingLanguageC++supportsavarietyofprogrammingstyles.Allarebasedonstrongstatictypechecking,andmostaimatachievingahighlevelofabstractionandadirectrepresentationoftheprogrammer'sideas.Eachstylecanachieveitsaimseffectivelywhilemaintainingrun-timeandspaceefficiency.C++ProgrammingLanguageAprogrammeroriginallyusingadifferentlanguage(sayC,Fortran,Smalltalk,Pascal,orModula-2)shouldrealizethattogainthebenefitsofC++,theymustspendtimelearningandinternalizingprogrammingstylesandtechniquessuitabletoC++.ThesamesituationappliestoprogrammersusedtoanearlierandlessexpressiveversionofC++.C++ProgrammingLanguageThoughtlesslyapplyingtechniqueseffectiveinonelanguagetoanothertypicallyleadstoawkward,poorlyperforming,andhard-to-maintaincode.Suchcodeisalsomostfrustratingtowritebecauseeverylineofcodeandeverycompilererrormessageremindstheprogrammerthatthelanguageuseddiffersfrom“theoldlanguage”.C++ProgrammingLanguageYoucanwriteinthestyleofFortran,C,Smalltalk,etcinanylanguage,butdoingsoisneitherpleasantnoreconomicalinalanguagewithadifferentphilosophy.EverylanguagecanbeafertilesourceofideasonhowtowriteC++programs.However,ideasmustbetransformedintosomethingthatfitswiththegeneralstructureandtypesystemofC++inordertobeeffectiveindifferentcontexts.C++ProgrammingLanguageC++supportsagradualapproachtolearning.Howyouapproachlearninganewprogramminglanguagedependsonwhatyoualreadyknowandwhatyouamtolearn.Thereisnosingleapproachthatsuitseveryone.MyassumptionisthatyouarelearingC++tobecomeabetterprogrammeranddesigner.Ergo,yourpurposeinlearningC++isnotsimplytolearnanewsyntaxfordoingthingsthewayyouusedto,buttolearnnewandbetterwaysofbuildingsystems.C++ProgrammingLanguageThishastobedonegraduallybecauseacquiringanysignificantnewskilltakestimeandrequirespractice.Considerhowlongitwouldtaketolearnanewnaturallanguagewellortolearntoplayanewmusicalinstrumentwell.Becomingabettersystemdesigneriseasierandfaster,butnotasmucheasierandfasterasmostpeoplewouldlikeittobe.C++ProgrammingLanguage谢谢观看C++面向对象程序设计双语教程(第3版)BasicFacilities—ShiftingfromCtoC++ProgramsC++面向对象程序设计双语教程(第3版)Chapter201C++ProgramStructureTheC++programconsistsofidentifiers，declarations，variables，constants，expressions，statements，andcomments.Acommonstructureforasimple，onefile，C++programincludesthefollowing：Comments.Theydescribeprogramfeature，author，andsoon.C++ProgramStructureIncludestatements.Theyspecifytheheaderfilesforlibraries.Usingnamespacestatement.Typically，thisisonly“usingnamespacestd”.Globaldeclarations（constants，types，variables，…）.Avoidglobalvariablesifpossible.C++ProgramStructureFunctionprototypes（declarations）.Mainfunctiondefinition.Functiondefinitions.C++ProgramStructureThefollowingexampleisusedtoillustrateaC++programstructure.Donotbetoo

concernedwiththedetailsintheprogram-justobserveitsover-alllookandstructure.C++ProgramStructureAllC++programscompriseoneormorefunctions，whicharealogicalgroupingofone

ormorestatements.Afunctionisidentifiedbyafunctionnameandafunctionbody.C++ProgramStructureAfunctionnameisidentifiedbyawordfollowedbyparentheses.InExample2-1，mainisafunctionname.Allprogramsmusthaveafunctioncalledmain.Theexeeutionofaprogrambeginswiththemainfunction.Thekeywordintalongwiththefunctionnamesignifiesthatthefunctionreturnsanintegervalue.C++ProgramStructureAfunctionbodyissurroundedbycurlybraces（{}）.Thebracesdelimitablockof

programstatements.Everyfunctionmusthaveapairofbraces.C++ProgramStructure02Input/Output

StreamsAprogramperformsthreebasicoperations：itgetsdata，itmanipulatesthedata，anditoutputtheresults.BecausewritingprogramsforI/Oisquitecomplex，C++offersextensivesupportforI/Ooperations.InC++，I/Oisasequenceofcharacters，calledastream，fromthe

sourcetothedestination.Input/OutputStreamsAstreamisasequenceofcharactersfromthesourcetothedestination.Inputstreamisasequenceofcharactersfromaninputdevice（e.g.keyboard）tothecomputer.Outputstreamisasequenceofcharactersfromthecomputertoanoutputdevice（e.g.monitor）.Input/OutputStreamsThestandardlibraryoffersistreamforinput.Theistreamdealswiththecharacterstring

representationsofbuilt-intypesandcaneasilybeextendedtocopewithuser-definedtypes.Withinputstreams，theextractionoperator（>>）isusedtoremovevaluesfromthestream.Thismakessense：whentheuserpressesakeyonthekeyboard，thekeycodeisplacedinan

inputstream.Yourprogramthenextractsthevaluefromthestreamsoitcanbeused.InputStreamInput/OutputStreamsThe>>operator（“getfrom”）isusedasaninputoperator；ein（readsee-in）isoneofthestandardInput/Outputstreams，i.e.iostream.Thetypeoftheright-handoperandof>>determineswhatinputisacceptedandwhatisthetargetoftheinputoperation.Input/OutputStreamsOutputStreamWithoutputstreams，theinsertionoperator（<<）isusedtoputvaluesinthestream.Thisalsomakessense：youinsertyourvaluesintothestream，andthedataconsumer（e.g.monitor）usesthem.Input/OutputStreamsOutputStreamThe<<operator（“putin”）areusedasanoutputoperation.cout（readsee-out）isalsooneofthestandardInput/Outputstreams，i.e.iostream.Bydefault，valuesoutputtocoutareconvertedtoasequenceofcharacters.Input/OutputStreams03ConstantsC++offerstheconceptofauser-definedconstant，aconst，toexpressthenotionthatthevalueofavariablecannotbechangeddirectly.Thisisusefulinseveralcontexts.Forexample，manyvariablesdonotactuallyhavetheirvalueschangedafterinitialization；symbolic

constantsleadtomoremaintainablecodethandoliteralsembeddeddirectlyincode；pointers

areoftenreadthroughbutneverwrittenthrough，andmostfunctionparametersarereadbut

notwrittento.ConstantsTheconstkeywordspecifiesthatavariable'svalueisconstantandtellsthecompilertopreventtheprogrammerfrommodifyingit.Itcanbeaddedtothedeclarationofavariabletodeclarethevariableasaconstant.ConstantsGiventhis，thecompilerknowsthevaluesofclandc2sothattheycanbeusedinconstantexpressions.Sincethevaluesofc3andc4arenotknownatcompiletime，storagemustbeallocatedfore3andc4.Becausetheaddressofc2istaken（andpresumablyusedsomewhere），storagemustbeallocatedforc2.ConstantsPointersandConstantsWhenusingapointer，twovariablesareinvolved：thepointeritselfandthevariablepointedto."Prefixing³thedeclarationofapointerwithconstmakesthevariable，butnotthepointer，aconstant.Todeclareapointeritself，ratherthantheobjectpointedto，tobeaconstant，weusethedeclaratoryoperator*constinsteadofplain*.Constants04FunctionsLetuslookbacktheprograminExample1-3ofChapter1.Whenyouworkonaprogram，itcanbedividedintoafewblockscalledfunetionbody.Sometimes，itisnotpracticaltoputtheentireprogramintoonefunction，e.g.themainfunction，asyouseeinExample1-3.Youmustlearntobreaktheproblemintomanageablepieces.FunctionsFunctionDeclarationsAfunctiondeclarationestablishesthenameofthefunction，thetypeofdatareturnedby

esofitsparameters.FunctionsAfunctiondeclarationconsistsofareturntype，aname，andaparameterlist.Inaddition，afunctiondeclarationmayoptionallyspecifythefunction'slinkage.InC++，thedeclarationcanalsospecifyanexceptionspecification，aconst-qualification，oravolatile-qualification.FunctionsAdeclarationinformsthecompileroftheformatandexistenceofafunctionpriortoitsuse.Afunctioncanbedeclaredseveraltimesinaprogram，providedthatallthedeclarationsarecompatible.Animplicitdeclarationofafunctionisnotallowed：everyfunctionmustbeexplicitlydeclaredbeforeitcanbecalled.FunctionsFunctionDeclarationsAfunctionargument（i.e.actualparameter）isanexpressionoravariablethatyouusewithinthe

parenthesesofafunctioncall.Afunetionparameter（i.e.formalparameter）isanobjeetorreferencedeclared

withintheparenthesisofafunctiondeclarationordefinition.FunctionsFunctionprototypesarerequiredforcompatibilitybetweenCandC++.Thenon-prototypeformofafunctionthathasanemptyparameterlistmeansthatthefunctiontakesanunknownnumberofparametersinC，whereas，inC++，itmeansthatittakesno

parameters.FunctionsFunctionDefinitionsAfunctiondefinitionconsistsofitsname，itsreturntype，itsparameterlistandbody.Thefunctionheaderspecifiesthefunction'sreturntype，nameandparameters.Thefunetionsignatureconsistsofthefunctionnameandtheparameterlist.FunctionsEveryfunctioninaprogrammustbedefinedsomewhere（onceonly）beforeitisinvoked.Afunctiondefinitionisafunctiondeclarationinwhichthebodyofthefunctionispresented.FunctionDefinitionsFunctionsDefaultArgumentsAgeneralfunctionoftenneedsmoreparametersthatarenecessarytohandlesimplecases.Inparticular，functionsthatconstructobjectsoftenprovideseveraloptionsforflexibility.FunctionsAdefaultargumentmeansthatthedefaultvaluesarepassedtotheparameterswhena

functionisinvokedwithoutthearguments.Ofcourse，theusercanchangethedefaultvalueif

heorsheprovidesavalueforthedefaultparameter.FunctionsInlineFunctionsAninlinefunctionisoneforwhichthecompilercopiesthecodefromthefunctiondefinitiondirectlyintothecodeofthecallingfunctionratherthancreatingaseparatesetofinstruetionsinmemory.Insteadoftransferringcontroltoandfromthefunctioncodesegment，amodifiedcopyofthefunctionbodymaysubstitutethefunctiondirectlyforthefunctioncall.Inthisway，theperformaneeoverheadofafunetioncallisavoided.FunctionsFunctionOverloadingMostoften，itisagoodideatogivedifferentfunctions

differentnames，butwhensomefunctionsconceptuallyperformthesametaskonobjectsofdifferenttypes，itcanbemofeconvenienttogivethemthesamename.Usingthesamenameforoperationsondifferenttypesiscalledoverloading.Functions05ReferencesReferenceDefinitionAreferenceisasimplereferencedatatype.Areferenceisanaliasoralternativenameforanobject.ThismeansthatC++allowsyoutocreateasecondnamefortheobjectthatyoucanusetoreadormodifytheoriginaldatastoredintheobject.ReferencesParametersprovideacommunicationlinkbetweenthecallingfunction（suchasmain）andthecalledfunction.Theyenablefunctionstomanipulatedifferentdataeachtimetheyarecalled.Ingeneral，therearetwotypesofformalparameters：valueparametersandreferenceparameters.ReferenceVariablesasParametersReferencesReferencesasReturningValuesReturningvaluesfromafunctiontoitscallerbyvalue，address，orreferenceworksalmost

the

same way

aspassingparameterstoafunction.Theyhavethesameadvantages

and

disadvantages.Theprimarydifferencebetweenthetwoissimplytheoppositedirectionsofdataflow.However，thereisonemoreaddedbitofcomplexity-becauselocalvariablesinafunctiongooutofscopewhenafunctionreturns，weneedtoconsidertheeffectofthisoneachretumtype.ReferencesReturningbyreferenceistypicallyusedtoreturnargumentspassedbyreferencetothe

functionbacktothecallerusedontheright-handsideofanassignmentoperator.Ifthefunctioncallcanappearontheleft-handsideofanassignmentoperator，whatwillhappen？ReferenceasLeft-HandValuesReferences06NamespacesAnamespaceisamechanismforexpressinglogicalgrouping，i.e.ifdeclarationslogically

belongtogetheraccordingtospecificcriteria，thenacommon namespace

expressthisfact.NamespacesInthisexample，variablesa，b，fanddaredeclaredwithintwonamespacescalledmySpaceandyourSpacerespectively.Althoughthesevariableshavethesamename，declaringthemwithinthetwonamespaceswillnotcausearedefinitionerror；thenamespaceisabletoavoidnamecollisions（ofvariables，types，elassesorfunctions）.NamespacesHerethefunctionbodiesaredefinedoutsidethenamespacesmySpaeeandyourSpace，theaimof

thisistoseparatetheinterface（ie.funetiondeelaration）fromtheimplementation（i.e.functiondefinition）.NamespacesAsaresultofseparatingtheimplementationoftheinterface，eachfunctionnowhasexactlyonedeclarationandonedefinition.Userswillseeonlytheinterfacecontainingdeclarations.Theimplementationinthiscase，thefunctionbodieswillbeplaces“somewhereelse³whereauserdoesnotneedtosee.Namespaces谢谢观看C++面向对象程序设计双语教程(第3版)FoundationofClassesandObjects—DataAbstractionandDefinitionofClassesC++面向对象程序设计双语教程(第3版)Chapter301IntroductiontoStructuresAstructuretypeisauser-definedtype.Structuresareaggregatedatatypebuiltbyusingelementsofothertypes，thatis，structuresareawayofstoringmanydifferentvaluesinvariablesofpotentiallydifferenttypesunderthesamename.Thismakesitamoremodularprogram，whichiseasiertomodifybecauseitsdesignmakesthingsmorecompact.Forexample，astructurecanbeusedtostoreinformationaboutstudentsinadatabase.IntroductiontoStructuresWhenyoudefineastructure，youmustrememberthatthemaindifferencebetweenstructuresandarraysisthatthestruetureisacollectionofdifferentdatatypesandthearrayisacollectionofthesamedatatype.IntroductiontoStructuresDefiningaStructureinC++Theprecedingstructuredefinitiondoesnotreserveanyspaceinmemory，rather，thedefinitioncreatesanewdatatypethatisusedtodeclareavariable.Structure'svariableis

declaredlikevariablesofothertypes.IntroductiontoStructuresTheprogramdefinesasingleDatestructurecalledt