计算机专业英语3.docx
- 文档编号:23142528
- 上传时间:2023-05-08
- 格式:DOCX
- 页数:5
- 大小:18.46KB
计算机专业英语3.docx
《计算机专业英语3.docx》由会员分享,可在线阅读,更多相关《计算机专业英语3.docx(5页珍藏版)》请在冰豆网上搜索。
计算机专业英语3
Unit3ComputerLanguageandProgramming
SectionAProgrammingLanguage
I.Introduction
Programminglanguages,incomputerscience,aretheartificiallanguagesusedtowriteasequenceofinstructions(acomputerprogram)thatcanberunbyacomputer.Similartonaturallanguages,suchasEnglish,programminglanguageshaveavocabulary,grammar,andsyntax.However,naturallanguagesarenotsuitedforprogrammingcomputersbecausetheyareambiguous,meaningthattheirvocabularyandgrammaticalstructuremaybeinterpretedinmultipleways.Thelanguagesusedtoprogramcomputersmusthavesimplelogicalstructures,andtherulesfortheirgrammar,spelling,andpunctuationmustbeprecise.
Programminglanguagesvarygreatlyintheirsophisticationandintheirdegreeofversatility.Someprogramminglanguagesarewrittentoaddress(处理)aparticularkindofcomputingproblemorforuseonaparticularmodelofcomputersystem.Forinstance,programminglanguagessuchasFORTRAN1andCOBOL2werewrittentosolvecertaingeneraltypesofprogrammingproblems—FORTRANforscientificapplications,andCOBOLforbusinessapplications.Althoughtheselanguagesweredesigntoaddressspecificcategoriesofcomputerproblems,theyarehighlyportable(可移植),meaningthattheymaybeusedtoprogrammanytypesofcomputers.Otherlanguages,suchasmachinelanguages,aredesignedtobeusedbyonespecificmodelofcomputersystem,orevenbyonespecificcomputerincertainresearchapplications.Themostcommonlyusedprogramminglanguagesarehighlyportableandcanbeusedtoeffectivelysolvediversetypesofcomputingproblems.LanguageslikeC,PASCALandBASICfallinto(属于)thiscategory.
II.LanguageTypes
Programminglanguagescanbeclassifiedaseitherlow-levellanguagesorhigh-levellanguages.Low-levelprogramminglanguages,ormachinelanguages,arethemostbasictypeofprogramminglanguagesandcanbeunderstooddirectlybyacomputer.Machinelanguagesdifferdependingonthemanufacturerandmodelofcomputer.High-levellanguagesareprogramminglanguagesthatmustfirstbetranslatedintoamachinelanguagebeforetheycanbeunderstoodandprocessedbyacomputer.Examplesofhigh-levellanguagesareC,C++6,PASCAL,andFORTRAN.Assemblylanguagesareintermediatelanguagesthatareveryclosetomachinelanguagesanddonothavetheleveloflinguisticsophisticationexhibitedbyotherhigh-levellanguages,butmuststillbetranslatedintomachinelanguage.
1.MachineLanguages
Inmachinelanguages,instructionsarewrittenassequencesof1sand0s,calledbits,thatacomputercanunderstanddirectly.Aninstructioninmachinelanguagegenerallytellsthecomputerfourthings:
(1)wheretofindoneortwonumbersorsimplepiecesofdatainthemaincomputermemory(RandomAccessMemory,orRAM),
(2)asimpleoperationtoperform,suchasaddingthetwonumberstogether,(3)whereinthemainmemorytoputtheresultofthissimpleoperation,and(4)wheretofindthenextinstructiontoperform.Whileallexecutableprogramsareeventuallyreadbythecomputerinmachinelanguage,theyarenotallprogrammedinmachinelanguage.Itisextremelydifficulttoprogramdirectlyinmachinelanguagebecausetheinstructionsaresequencesof1sand0s.Atypicalinstructioninamachinelanguagemightread1001011001011andmeanaddthecontentsofstorageregisterAtothecontentsofstorageregisterB.
2.High-LevelLanguages
High-levellanguagesarerelativelysophisticatedsetsofstatementsutilizingwordsandsyntaxfromhumanlanguage.Theyaremoresimilartonormalhumanlanguagesthanassemblyormachinelanguagesandarethereforeeasiertouseforwritingcomplicatedprograms.Theseprogramminglanguagesallowlargerandmorecomplicatedprogramstobedevelopedfaster.However,high-levellanguagesmustbetranslatedintomachinelanguagebyanotherprogramcalledacompilerbeforeacomputercanunderstandthem.Forthisreason,programswritteninahigh-levellanguagemaytakelongertoexecuteanduseup(用完)morememorythanprogramswritteninanassemblylanguage.
3.AssemblyLanguages
Computerprogrammersuseassemblylanguagestomakemachine-languageprogramseasiertowrite.Inanassemblylanguage,eachstatementcorrespondsroughlytoonemachinelanguageinstruction.Anassemblylanguagestatementiscomposedwiththeaidof(借助于,帮助)easytoremembercommands.ThecommandtoaddthecontentsofstorageregisterAtothecontentsofstorageregisterBmightbewrittenADDB,Ainatypicalassemblylanguagestatement.Assemblylanguagessharecertainfeatureswithmachinelanguages.Forinstance,itispossibletomanipulatespecificbitsinbothassemblyandmachinelanguages.Programmersuseassemblylanguageswhenitisimportanttominimizethetimeittakestorunaprogram,becausethetranslationfromassemblylanguagetomachinelanguageisrelativelysimple.Assemblylanguagesarealsousedwhensomepartofthecomputerhastobecontrolleddirectly,suchasindividualdotsonamonitorortheflowofindividualcharacterstoaprinter.
III.ClassificationofHigh-LevelLanguages
High-levellanguagesarecommonlyclassifiedasprocedure-oriented,functional,object-oriented,orlogiclanguages.Themostcommonhigh-levellanguagestodayareprocedure-orientedlanguages.Inlanguages,oneormorerelatedblocksofstatementsthatperformsomecompletefunctionaregroupedtogetherintoaprogrammodule,orprocedure,andgivenanamesuchas"procedureA."Ifthesamesequenceofoperationsisneededelsewhereintheprogram,asimplestatementcanbeusedtoreferbacktotheprocedure.Inessence,aprocedureisjustamini-program.Alargeprogramcanbeconstructedbygroupingtogetherproceduresthatperformdifferenttasks.Procedurallanguagesallowprogramstobeshorterandeasierforthecomputertoread,buttheyrequiretheprogrammertodesigneachproceduretobegeneralenoughtobeuseindifferentsituations.
Functionallanguagestreatprocedureslikemathematicalfunctionandallowthemtobeprocessedlikeanyotherdatainaprogram.Thisallowsamuchhigherandmorerigorouslevelofprogramconstruction,Functionallanguagesalsoallowvariables—symbolsfordatathatcanbespecifiedandchangedbytheuserastheprogramisrunning—tobegivenvaluesonlyonce.Thissimplifiesprogrammingbyreducingtheneedtobeconcernedwiththeexactorderofstatementexecution,sinceavariabledoesnothavetoberedeclared,orrestated,eachtimeitisusedinaprogramstatement.Manyoftheideasfromfunctionallanguageshavebecomekey|partsofmanymodemprocedurallanguages.
Object-orientedlanguagesareoutgrowthsoffunctionallanguages.Inobject-orientedlanguages,thecodeusedtowritetheprogramandthedataprocessedbytheprogramaregroupedtogetherintounitscalledobjects,Objectsarefurthergroupedintoclasses,whichdefinetheattributesobjectsmusthave.AsimpleexampleofaclassistheclassBook.ObjectswithinthisclassmightbeNovelandShortStory.Objectsalsohavecertainfunctionsassociatedwiththem,calledmethods.Thecomputeraccessesanobjectthroughtheuseofoneoftheobject'smethods.Themethodperformssomeactiontothedataintheobjectandreturnsthisvaluetothecomputer.Classesofobjectscanalsobefurthergroupedintohierarchies,inwhichobjectsofoneclasscaninheritmethodsfromanotherclass.Thestructureprovidedinobject-orientedlanguagesmakesthemveryusefulforcomplicatedprogrammingtasks.
Logiclanguagesuselogicastheirmathematicalbase.Alogicprogramconsistsofsetsoffactsandif-thenrules,whichspecifyhowonesetoffactsmaybededucedfrom(推断)others,forexample:
IfthestatementXistrue,thenthestatementYisfalse.
Intheexecutionofsuchaprogram,aninputstatementcanbelogicallydeducedfromotherstatementsintheprogram.Manyartificialintelligenceprogramsarewritteninsuchlanguages.
IV.LanguageStructureandComponents
Programminglanguagesusespecifictypesofstatements,orinstructions,toprovidefunctionalstructuretotheprogram.Astatementinaprogramisabasicsentencethatexpressesasimpleidea—itspurposeistogivethecomputerabasicinstruction.Statementsdefinethetypesofdataallowed,howdataaretobemanipulated,andthewaysthatproceduresandfunctionswork.Programmersusestatementstomanipulatecommoncomponentsofprogramminglanguages,suchasvariablesandmacros(mini-programswithinaprogram).
Statementsknownasdatadeclarationsgivenamesandpropertiestoelementsofaprogramcalledvariables.Variablescanbeassigneddifferentvalueswithintheprogram.Thepropertiesvariablescanhavearecalledtypes,andtheyincludesuchthingsaswhatpossiblevaluesmightbesavedinthevariables,howmuchnumericalaccuracyistobeusedinthevalues,andhowonevariablemayrepresentacollectionofsimplervaluesinanorganizedfashion,suchasatableorarray.Inmanyprogramminglanguages,akeydatatypeisapointer.Variablesthatarepointersdonotthemselveshavevalues;instead,theyhaveinformationthatthecomputercanusetolocatesomeothervariable—thatis,theypointtoanothervariable.
Anexpressionisapieceofastatementthatdescribesaseriesofcomputationstobeperformedonsomeoftheprogram'svariables,suchasX+Y/Z,inwhichthevariablesareX,Y,andZandthecomputationsareadditionanddivision.Anassignmentstatementassignsavariableavaluederivedfrom(得自)someexpression,whileconditionalstatementsspecifyexpressionstobetestedandthenusedtoselectwhichotherstatementsshouldbeexecutednext.
Procedureandfunctionstatementsdefinecertainblocksofcodeasproceduresorfunct
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 计算机专业 英语