Pascal Tutorial 过程式编程语言.docx

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1、PascalTutorial-IntroIntroductionIFYOUKNOWNOTHINGABOUTPASCA1.AssumingthatyouknownothingatallaboutPascal,andinfact,thatyoumayknownothingaboutprogrammingingeneral,wewillbegintostudyPascal.IfyouarealreadysomewhatfamiliarwithprogrammingandespeciallyPascal,youW川probablywanttoskipveryquicklythroughthefirst

2、fewchapters.Youshouldatleastskimthesechapters,andyoushouldreadtheremainderofthisintroduction.Afewcommentsareinordertogetusstartedintherightdirection.ThesampleprogramsincludedwiththistutorialaredesignedtoteachyouthebasicsofPascalandtheydonotincludeanycleverortrickycode.Nearlyalloftheprogramsarereally

3、quitedumbasfarasbeingusefulprograms,butallwillteachoneormoreprinciplesofPascal.Ihaveseenonetutorialthatincludeda12pageprogramasthefirstexample.Infacttherewereonly2exampleprogramsintheentiretutorial,anditwasimpossibletogleantheessentialsofprogrammingfromthatsystem.Forthisreason,Iwillcompletelybypassa

4、nylongprogramsuntiltheveryendofthistutorial.Inorderto川UStratefundamentalconceptsusedinPascalprogramming,allprogramswillbeveryshortandconciseuntilwereachthelastchapter.1.ARGERPASCA1.PROGRAMSChapter16hassomeratherlargeprogramstoillustratetoyouhowtowritealargeprogram.Itwouldbeadisservicetoyoutoshowyoua

5、lloftheconstructsofPascalandnotshowyouhowtoputthemtogetherinameaningfulwaytobuildalargeprogram.AftercompletingallofthefundamentalsofPascal,itwillthenbeveryeasyforyoutousethetoolslearnedtobuildaslargeaprogramasyoudesireorrequireforyournextprogrammingproject.AnotherproblemIhavenoticedinexampleprograms

6、istheuseofonewordforalldefinitions.Forexample,asortprogramisstoredinafilecalledSORT,theprogramisnamedSort,andvariouspartsoftheprogramarereferredtoasSortl1Sort2,etc.Thiscanbeconfusingsinceyouhavenoideaiftheprogramnamemustbethesameasthefilename,orifanyoftheothernameswerechosentobethesamebecauseofsomeo

7、bscurerulenotclearlydocumented.Forthisreason,theexampleprogramsusecompletelyarbitrarynameswheneverthechoiceofanameaddsnothingtothereadabilityorclarityofaprogram.Asan川UStrationofthistthefirstprogramisnamedPuppy_Dog.Thisaddsnothingtotheunderstandingoftheprogrambutdoesillustratethattheprogramnamemeansn

8、othingtothePascalcompilerconcerningwhattheprogramdoes.DuetothefundamentaldesignofthePascallanguage,certainwordsarereservedandcanonlybeusedfortheirdefinedpurposes.ThesearelistedinyorTURBOPascalreferencemanual.Allofthesampleprogramsinthistutorialarewrittenwiththereservedwordsinalllower-caseletters,and

9、theuservariablesinlowercasewiththefirstlettercapitalizedsincethisisbecominganacceptedindustrystandard.Dontworryaboutwhatreservedwordsareyet,theywillbecompletelydefinedlater.Inthistutorial,allreservedwords,typenames,variablenames,andprocedureandfunctionnameswillbelistedinboldfacetypewithinthetextasan

10、aidtothestudent.whatIsacompiler?TherearetwomethodsusedtorunanycomputerprogramthatiswritteninareadableformofEnglish.Thefirstmethodistouseaninterpreter.AninterpreterisaprogramthatlooksateachlineoftheEnglishprogram,decideswhattheEnglishonthatlinemeans,anddoeswhatitsaystodo.Ifoneofthelinesisexecutedrepe

11、atedly,itmustbescannedandanalyzedeachtime,greatlyslowingdownthesolutionoftheproblemathand.Acompiler,ontheotherhand,isaprogramthatlooksateachEnglishstatementonetimeandconvertsitintoacodethatthecomputerunderstandsdirectly.Whenthecompiledprogramisactuallyrun,thecomputerdoesnothavetofigureoutwhateachsta

12、tementmeans,itisalreadyinaformthatthecomputercanrundirectly,resultinginmuchfasterexecutionoftheprogram.ThistutorialiswrittenespeciallyforBorlandInternationalsTURBOPascalcompilersversion5.0through7.0.Theseareveryhighqualitycompilersthatcandonearlyanythingyouwillaskthemtodosincetheyaresoflexible.Theor

13、iginalintentofthistutorialwastowriteitinsuchawaythatitwouldbecompletelygenericandusablewithanygoodPascalcompiler.TheprogrammersatBorlandincludedagreatmanynonstandardaidsforthePascallanguageandresultedinaverygoodproductthathasdominatedthemarketformicrocomputers.Tocompletelyomitalloftheextensionswould

14、dothoseofyouwiththeBorlandcompilerarealdisservice,andtoincludetheextensionswouldnotallowothercompilerstobeusedeffectivelywiththistutorial.ThedecisionwasmadetousetheBorlandextensionswhichmaymakethetutorialdifficulttousewithothercompilers.IfyouhaveaneedtousePascalwithsomeothercompiler,TURBOPascalissoi

15、nexpensivethatitwouldbeawisedecisiontopurchaseacopysolelyforthepurposeoflearningthePascalprogramminglanguage,thenmovingtotheothercompileronaminicomputeroramainframeusingtheaccumulatedknowledgetoveryquicklylearntheextensionsprovidedbythatparticularcompiler.Atanyrate,thistutorialwillnotteachyoueveryth

16、ingyouwilleverneedtoknowaboutPascal.Itwill,however,teachyouthefundamentalsandtheadvancedfeaturesofPascal,butofevenmoreimportanceistheknowledgeofPascalterminologyneededtoprogressonyourownintomoreadvancedtopicsofPascalandprogrammingingeneral.Youwillfindthatexperiencewillbeyourbestteacher.WHICHVERSIONO

17、FTURBOPASCA1.?SomeoftheexampleprogramswillnotworkwithsomeoftheearlierversionsofTURBOPascal.Thisisprimarilyduetothefactthatobjectorientedprogrammingcapabilitieswereaddedtoversion5.5,andimprovedoninlaterversions.Mostoftheexampleprogramswillworkwithanyversionhowever.Itshouldbepointedoutthateachsuccessi

18、veversionofTURBOPascalhasbeenanimprovementoverthepreviousversionsinceadditionalcapabilitieshavebeenadded,andeachnewonecompilesalittlefasterandresultsinsmallerbutfasterexecutablecodethanthepreviousversion.AnyoftheversionsofTURBOPascalcanbeusedtolearntoprograminPascal,sowhicheverversionyouhaveonhandwi

19、llbeadequate.1.ater,whenyoubecomemoreversedinprogrammingtechniques,youmaywishtoupgradetotheabsolutelatestversion.EAR1.YVERSIONSOFTURBOPASCA1.MostofthefileswillcompileproperlywithTURBOPascalversions2.0through4.0.Nowarningwillbegivenaboutwhichfileswillnotcompilewiththeseversionssincetheyhavebeensupers

20、ededforsolong.Ifyouarestillusingoneoftheearlierversions,itwouldbegoodforyoutopurchaseanewerversionbecauseoftheflexibility.WHATABOUTTURBOPASCA1.VERSION5.5&NEWER?Chapters14and15ofthistutorialarewrittenespeciallyforTURBOPascalversion5.5andnewertodiscusstheuseofobjectorientedprogrammingandhowtousetheBor

21、landextensions.Sincethetopicofobjectorientedprogrammingisaverylargeanddiversefieldofstudyandonlyalimitedspaceisavailabletodiscussitinthistutorial,thesechapterswillgiveyouonlyabriefoverviewofwhatitisandhowtouseit.Youwillfind13completeexampleprogramstogetyoustartedinthisnewandverymeaningfulendeavorand

22、thisintroductionshouldwhetyourappetitetocontinueyourstudyinmoredepth.IfyouareusinganearlyversionofTURBOPascalwithouttheobjectorientedextensions,itwouldpayyoutoupgradesoyoucanlearnhowtousethisnewprogrammingmethod.Objectorientedprogramminghasthepotentialtogreatlyimprovethequalityofyourcodeandtoreducet

23、hedebuggingtimerequired.PREPARATIONFORUSEOFTHISTUTORIA1.CopytheexamplefilesintoyourTURBOPascalworkingdirectoryandyouarereadytobegin,providedofcoursethatyouhavealreadylearnedhowtostarttheTURBOsystemandhowtoeditaPascalfile.IfyouarenotusingTURBOPascal,youwillstillbeabletocompileandexecutemanyofthesePas

24、calfiles,sincemostoftheexamplesusestandardPascalsyntax.TherewillbesomestatementsusedwhichareuniquetoTURBOPascalandwillnotworkwithyourcompiler.Thiswillbeespeciallytruewhenyoucometothechapteronstandardinputandoutputsincethisiswheremostcompilersdiffer.Unfortunately,thisisoneofthemostimportantaspectsofa

25、nyprogramminglanguage,sinceitisrequiredtogetdataintoandoutofthecomputertodoanythinguseful.Youwillalsofindthatchapter13,coveringthetopicofunits,isuniquetoTURBOPascalandwillnotworkwithanyPascalcompilersotherthanTURBOPascal.WHATABOUTTHEPROGRAMMINGEXERCISES?Itishighlysuggestedthatyoudotheprogrammingexer

26、cisesafteryoucompletethestudyforeachchapter.Theyarecarefullyselectedtotestyourunderstandingofthematerialcoveredinthatchapter.Ifyoudonotwrite,enter,debug,andruntheseprograms,youW川OnlybeproficientatreadingPascal.Ifyoudotheexercisescompletely,youwillhaveagoodstartatbeingaPascalprogramwriter.Itshouldals

27、obementionedthatthistutorialwillnotteachyoueverythingyouwilleverneedtoknowaboutPascal.Youwillcontinuetolearnnewtechniquesaslongasyoucontinuetowriteprograms.Experienceisthebestteacherherejustasitisinanyendeavor.ThistutorialwillteachyouenoughaboutPascalthatyoushouldfeelverycomfortableasyousearchthroug

28、hthereferencemanualforsometopic.YouwillalsobeabletoreadandunderstandanyPascalprogramyoufindintextbooksormagazines.AlthoughtheprimarygoalofthistutorialistoteachyouthesyntaxanduseofPascal,themostimportantbyproductistheknowledgeofPascalterminologyyouwillgain.Thisterminologywillenableyoutolearnevenmorea

29、boutPascalandprogrammingingeneral.THEANSWERSTOPROGRAMMINGEXERCISESThefilepasans.zipcontainsananswertoeachoftheprogrammingexercisesgivenattheendofthechapters.Youshouldattempttodooriginalworkoneachoftheexercisesbeforereferringtotheseanswers,inordertogainyourownprogrammingexperience.Theseanswersaregive

30、nforyourinformationincaseyouarecompletelystuckonhowtosolveaparticularproblem.Theseanswersarenotmeanttobetheonlyanswer,sincetherearemanywaystoprogramanything,buttheyaremeanttoillustrateonewaytosolvethesuggestedprogrammingproblem.TheanswersareallincompilablefilesnamedintheformatCHnn_m.PASwhereisthecha

31、pternumber,andmistheexercisenumber.Ifthereismorethanoneanswerrequired,anA,B,orCisincludedfollowingtheexercisenumber.AdVanCetoChaPter1RetUmtotheTableOfContentsCopyright1986-1997CoronadoEnterprises-1.astupdate,March16,1997GordonDodriH-dodrill-PleaSeemailanycommentsorSIlggeStiOns.PascalTutorial-Chapter

32、1WhatIsAComputerProgram?THISCHAPTERISFORNEWPROGRAMMERSIfyouareacompletenovicetocomputersyouwillfindtheinformationinthischapteruseful.Ifhowever,youhavehadsomeexperiencewithprogramming,youcancompletelyignorethischapter.Itwilldealwithafewfundamentalsofcomputersingeneralandwillintroducenothingthatisspec

33、ifictoPascal.WHATISACOMPUTERPROGRAM?Acomputerisnothingbutaverydumbmachinethathastheabilitytoperformmathematicaloperationsveryrapidlyandveryaccurately,butitcandonothingwithouttheaidofaprogramwrittenbyahumanbeing.Moreover,ifthehumanbeingwritesaprogramthatturnsgooddataintogarbage,thecomputerwillveryobe

34、diently,andveryrapidly,turnthegooddataintogarbage.Itispossibletowriteacomputerprogramwithonesmallerrorinitthatwilldothatverything,andinsomecasesappeartobegeneratinggooddata.Itisuptothehumanprogrammertodesignaprogramtoachievethedesiredresults.Acomputerprogramissimplyarecipewhichthecomputerwilluseonth

35、einputdatatoderivethedesiredoutputdata.Itissimilartotherecipeforbakingacake.Theinputdataiscomparabletotheingredients,includingtheheatsuppliedbytheoven.Theprogramiscomparabletotherecipeinstructionstomix,stir,wait,heat,cool,andallotherpossibleoperationsontheingredients.Theoutputofthecomputerprogramcan

36、becomparedtothefinalcakesittingonthecounterreadytobecutandserved.Acomputerprogramisthereforecomposedoftwoparts,thedatauponwhichtheprogramoperates,andtheprogramthatoperatesonthedata.Thedataandprogramareinseparableasimpliedbythelastsentence.WHATARECONSTANTS?Nearlyanycomputerprogramrequiressomenumberst

37、hatneverchangethroughouttheprogram.Theycanbedefinedonceandusedasoftenasneededduringtheoperationoftheprogram.Toreturntotherecipeanalogy,onceyouhavedefinedhowbigatablespoonis,youcanusethesametablespoonwithoutregardtowhatyouaremeasuringwithit.Whenwritingacomputerprogram,youcandefinethevalueofPl=3.14159

38、2,andcontinuetouseitwhereveritmakessenseknowingthatitisavailable,andcorrect.WHATAREVARIAB1.ES?Inadditiontoconstants,nearlyeverycomputerprogramusessomenumbersthatchangeinvaluethroughouttheprogram.Theycanbedefinedasvariables,thenchangedtoanyvaluesthatmakesensetotheproperoperationoftheprogram.Anexample

39、wouldbethenumberofeggsintheaboverecipe.Ifasinglelayerofcakerequired2eggs,thenatriplelayercakewouldrequire6eggs.Thenumberofeggswouldthereforebeavariable.HOWDOWEDEFINECONSTANTSORVARIAB1.ES?Allconstantsandvariableshaveanameandavalue.Inthelastexample,thenameofthevariablewaseggs,andthevaluewaseither2or6d

40、ependingonwhenwelookedatthestoreddata.Inacomputerprogramtheconstantsandvariablesaregivennamesinmuchthesamemanner,afterwhichtheycanstoreanyvaluewithinthedefinedrange.Anycomputerprogramminglanguagehasameansbywhichconstantsorvariablescanbefirstnamed,thenassignedavalue.ThemeansfordoingthisinPascalwillbe

41、giventhroughouttheremainderofthistutorial.WHATISSOGOODABOUTPASCA1.?Somecomputerlanguagesallowtheprogrammertodefineconstantsandvariablesinaveryhaphazardmannerandthencombinedatainanevenmorehaphazardmanner.Forexample,ifyouaddedthenumberofeggs,intheaboverecipe,tothenumberofcupsofflour,youwouldarriveatav

42、alidmathematicaladdition,butatotallymeaninglessnumber.Someprogramminglanguageswouldallowyoutodojustsuchanadditionandobedientlyprintoutthemeaninglessanswer.SincePascalrequiresyoutosetupyourconstantsandvariablesinaveryprecisemanner,thepossibilityofsuchameaninglessanswerisminimized.AwellwrittenPascalpr

43、ogramhasmanycrosscheckstominimizethepossibilityofacompletelyscrambledandmeaninglessoutput.Noticehowever,inthelaststatement,thatawellwrittenPascalprogramwasunderdiscussion.Itisstilluptotheprogrammertodefinethedatastructureinsuchawaythattheprogramcanhelppreventgarbagegeneration.Intheend,theprogramwill

44、benobetterthantheanalysisthatwentintotheprogramdesign.Ifyouareanoviceprogrammer,donotbeintimidatedbyanyoftheabovestatements.Pascalisawelldesigned,usefultoolthathasbeenusedsuccessfullybymanycomputernovicesandprofessionals.Withthesefewwarnings,youarereadytobegin.AdVanCetoChaPter2RetUmtotheTabIeOfCC)me

45、ritsCopyright1986-1997CoronadoEnterprises-1.astupdate,March16,1997GordonDodriH-dodriH-PleaSeemailanycommentsOrSUqqeStiOns.PascalTutorial-Chapter2GettingStartedInPascalYOURFIRSTPASCA1.PROGRAMExampleprogramTRIVIA1.PAS1.etsgetrightintoaprogramthatreallydoesnothing,butisanexampleofthemosttrivialPascalpr

46、ogram.1.oadTurboPascal,thenloadTRIVIA1.PASintotheintegratedenvironmentasaworkfile.ThisassumesyouhavebeensuccessfulinlearninghowtousetheTURBOPascalsystem.YoushouldnowhavethemosttrivialPascalprogrampossibleonyourdisplay,andwecantakealookateachparttodefinewhatitdoes.ThefirstlineisrequiredinthestandardP

47、ascaldefinitionandcontainstheprogramnamewhichcanbeanynameyoulike,aslongasitfollowstherulesforanidentifiergiveninthenextsection.Itcanhavenoblanks,otherwiseitwouldbeconsideredastwowordsanditwouldconfusethecompiler.ThefirstwordprogramisthefirstofthereservedwordsmentionedearlieranditistheindicatortotheP

48、ascalcompilerthatthisisthenameoftheprogram.Thesecondword,Puppy_Dog,istheprogramnameitself.Noticethatthelineendswithasemicolon.Pascalusesthesemicolonasastatementseparatorandalthoughallstatementsdonotactuallyendinasemicolon,mostdo,andtheproperuseofthesemicolonwillclearuplaterinyourmind.TURBOPascaldoes

49、notrequiretheprogramstatement,buttoremaincompatiblewithstandardPascal,itwillsimplyignoretheentirestatement.ItisrecommendedthatyouincludeaprogramnamebothtoaidyourthinkinginstandardPascal,andtoaddalittlemoreindicationofthepurposeofeachprogram.WHATISANIDENTIFIER?Allidentifiers,includingtheprogramname,procedureandfunctionnames,typedefinitions,andconstantandvariablenames,willstartwithanalphabeticalcharacterandbecomposedofanycombination