《计算机专业英语》-Unit5TheProgrammingLanguages

TextA:ProgrammingFundamentals下一页返回TextA:ProgrammingFundamentalsTheprogramminglanguageisthevocabularyandsetofgrammaticalrulesforinstructingacomputertoperformspecifictasks.Thetermprogramminglanguageusuallyreferstohigh-levellanguage,suchasBASIC,C,C++,COBOL,FORTRAN,Ada,andPascal.Eachlanguagehasauniquesetofkeywords(wordsthatitunderstands)andaspecialsyntaxfororganizingprograminstructions.上一页下一页返回TextA:ProgrammingFundamentalsHigh-levelprogramminglanguages,whilesimplecomparedtohumanlanguages,aremorecomplexthanthelanguagesthecomputeractuallyunderstands,whicharecalledmachinelanguages.EachdifferenttypeofCPUhasitsownuniquemachinelanguage.Lyingbetweenmachinelanguagesandhigh-levellanguagesarelanguagescalledassemblylanguages.Assemblylanguagesaresimilartomachinelanguages,buttheyaremucheasiertoprograminbecausetheyallowaprogrammertosubstitutenamesfornumbers.Machinelanguagesconsistofnumbersonly.上一页下一页返回TextA:ProgrammingFundamentalsLyingabovehigh-levellanguagesarelanguagescalledfourth-generationlanguages(usuallyabbreviated4GL).4GLsarefarremovedfrommachinelanguagesandrepresenttheclassofcomputerlanguagesclosesttohumanlanguages.Regardlessofwhatlanguageyouuse,youeventuallyneedtoconvertyourprogramintomachinelanguagesothatthecomputercanunderstandit.Therearetwowaystodothis.上一页下一页返回TextA:ProgrammingFundamentals(1)TocompiletheprogramHere,itistotransformaprogramwritteninahigh-levelprogramminglanguagefromsourcecodeintoobjectcode.Programmerswriteprogramsinaformcalledsourcecode.Sourcecodemustgothroughseveralstepsbeforeitbecomesanexecutableprogram.Thefirststepistopassthesourcecodethroughacompiler,whichtranslatesthehigh-levellanguageinstructionsintoobjectcode.上一页下一页返回TextA:ProgrammingFundamentalsThefinalstepinproducinganexecutableprogram—afterthecompilerhasproducedobjectcode—istopasstheobjectcodethroughalinker.Thelinkercombinesmodulesandgivesrealvaluestoallsymbolicaddresses,therebyproducingmachinecode.上一页下一页返回TextA:ProgrammingFundamentals(2)TointerprettheprogramAninterpretertranslateshigh-levelinstructionsintoanintermediateform,whichitthenexecutes.Incontrast,acompilertranslateshigh-levelinstructionsdirectlyintoamachinelanguage.Compiledprogramsgenerallyrunfasterthaninterpretedprograms.Theadvantageofaninterpreter,however,isthatitdoesnotneedtogothroughthecompilationstageduringwhichmachineinstructionsaregenerated.Thisprocesscanbetime-consumingiftheprogramislong.Theinterpreter,ontheotherhand,canimmediatelyexecutehigh-levelprograms.Forthisreason,interpretersaresometimesusedduringthedevelopmentofaprogram,whenaprogrammerwantstoaddsmallsectionsatatimeandtestthemquickly.Inaddition,interpretersareoftenusedineducationbecausetheyallowstudentstoprograminteractively.上一页下一页返回TextA:ProgrammingFundamentalsBothinterpretersandcompilersareavailableformosthigh-levellanguages.However,BASICandLISPareespeciallydesignedtobeexecutedbyaninterpreter.Inaddition,pagedescriptionlanguages,suchasPostScript,useaninterpreter.EveryPostScriptprinter,forexample,hasabuiltininterpreterthatexecutesPostScriptinstructions.上一页下一页返回TextA:ProgrammingFundamentalsThequestionofwhichlanguageisbestisonethatconsumesalotoftimeandenergyamongcomputerprofessionals.Everylanguagehasitsstrengthsandweaknesses.Forexample,FORTRANisaparticularlygoodlanguageforprocessingnumericaldata,butitdoesnotlenditselfverywelltoorganizinglargeprograms.Pascalisverygoodforwritingwellstructuredandreadableprograms,butitisnotasflexibleastheCprogramminglanguage.C++embodiespowerfulobjectorientedfeatures,butitiscomplexanddifficulttolearn.Thechoiceofwhichlanguagetousedependsonthetypeofcomputertheprogramistorunon,whatsortofprogramitis,andtheexpertiseoftheprogrammer.上一页下一页返回TextA:ProgrammingFundamentalsWordsandExpressionsprogramminglanguage:编程语言；程序设计语言keyword:n.关键字syntax:n.语法；句法comparedto:与……相比machinelanguage:n.机器语言assemblylanguage:n.汇编语言substitute:vt.代替fourthgenerationlanguage:第4代语言represent:vt.代表compile:vt.编制；编辑

上一页下一页返回TextA:ProgrammingFundamentalssourcecode:源代码objectcode:目标代码executableprogram:可执行程序linker:n.连接器；链接程序module:n.模块；组件value:n.值；参数symbolicaddress:符号地址machinecode:机器代码，机器编码上一页下一页返回TextA:ProgrammingFundamentalsinterpreter:n.翻译器(参考compiler：编译器)intermediate:adj.中间的，中级的interactively:adv.交互式地builtin:adj.嵌入的;固定的n.内置strength:n.优势；优点weakness:n.劣势；缺点numericaldata:数值数据readable:adj.可读的flexible:adj.灵活的；可变通的；有弹性的embody:vt.体现expertise:n.专门知识；专门技术上一页下一页返回TextA:ProgrammingFundamentalsNotes①Assemblylanguagesaresimilartomachinelanguages,buttheyaremucheasiertoprograminbecausetheyallowaprogrammertosubstitutenamesfornumbers.Machinelanguagesconsistofnumbersonly.②Regardlessofwhatlanguageyouuse,youeventuallyneedtoconvertyourprogramintomachinelanguagesothatthecomputercanunderstandit.③Thechoiceofwhichlanguagetousedependsonthetypeofcomputertheprogramistorunon,whatsortofprogramitis,andtheexpertiseoftheprogrammer.上一页返回TextB:ProgramDevelopmentToolsProgramminglanguagesareclassifiedintofivemajorcategories:machinelanguages,assemblylanguages,thirdgenerationlanguages,fourthgenerationlanguages,andnaturallanguages.Machineandassemblylanguagesarereferredtoaslowlevellanguages;thirdgeneration,fourthgenerationandnaturallanguagesarecalledhighlevellanguages.Alowlevellanguageiswrittentorunononeparticularcomputer.Ahighlevellanguagecanrunonmanydifferenttypesofcomputer.下一页返回TextB:ProgramDevelopmentTools1.MachineLanguagesMachinelanguage,whichisalsocalledthefirstgenerationlanguage,sometimesreferredtoasmachinecodeorobjectcode,isacollectionofbinarydigitsorbits(1sand0s)thatthecomputerreadsandinterprets.Machinelanguageistheonlylanguageacomputeriscapableofunderstanding.Moreover,machinelanguageprogramsrunonlyonthecomputerforwhichtheyweredeveloped,thatis,theyaremachinedependent.Onedisadvantageofmachinelanguageprogramsthenisthattheyarenotportabletoothercomputers.Second,asyoumightimagine,codinginthe1sand0sofmachinelanguagecanbetediousandtimeconsuming.上一页下一页返回TextB:ProgramDevelopmentTools2.AssemblyLanguagesBecausemachinelanguageprogramsaresodifficulttowrite,thesecondgenerationofprogramminglanguages,calledassemblylanguages,evolved.Assemblylanguageswerefirstdevelopedinthe1950s,whentheywerereferredtoassecondgenerationprogramminglanguages.Theyeliminatedmuchoftheerrorproneandtimeconsumingproceduresfirstgenerationprogrammingneededwiththeearliestcomputers,freeingtheprogrammerfromtediumsuchasrememberingnumericcodesandcalculatingaddresses.Withanassemblylanguage,instructionswerewrittenusingabbreviations.Aswithmachinelanguages,assemblylanguagesareoftendifficulttolearnandaremachinedependent.上一页下一页返回TextB:ProgramDevelopmentToolsAssemblylanguagesdohaveseveraladvantagesovermachinelanguages.Insteadofusingaseriesofbits,theprogrammerusesmeaningfulabbreviationsforprograminstruction,calledsymbolicinstructioncodes,ormnemonics.Withanassemblylanguage,aprogrammerwritescodessuchasAforaddition,Cforcompare,Lforload,andMformultiply.Anotheradvantageofassemblylanguageisthattheprogrammercanrefertostoragelocationswithsymbolicaddresses.Forexample,insteadofusingtheactualnumericstorageaddressofaunitprice,aprogrammercanusethesymbolicnamePRICE.上一页下一页返回TextB:ProgramDevelopmentToolsOnedisadvantageofanassemblylanguageprogramisthatitmustbetranslatedintomachinelanguagebeforethecomputercanunderstandit.Theprogramcontainingtheassemblylanguagecodeiscalledthesourceprogram.Thecomputercannotunderstandorexecutethissourceprogramuntilitistranslated.Autilityprogramcalledanassemblerisusedtotranslateassemblylanguagestatementsintothetargetcomputer’smachinecode.Theassemblerperformsamoreorlessisomorphictranslation(aonetoonemapping)frommnemonicstatementsintomachineinstructionsanddata.上一页下一页返回TextB:ProgramDevelopmentTools3.ThirdGenerationLanguagesTheintroductionofthecompilerin1952spurredthedevelopmentofthirdgenerationcomputerlanguages.TheselanguagesenableaprogrammertocreateprogramfilesusingcommandsthataresimilartospokenEnglish.Thirdgenerationcomputerlanguageshavebecomethemajormeansofcommunicationbetweenthedigitalcomputeranditsuser.上一页下一页返回TextB:ProgramDevelopmentToolsInformationinasourceprogramisconvertedintotheobjectprogrambyanintermediateprogramcalledaninterpreterorcompiler.Aninterpreterisaprogramthatconverts(orexecutes,inprogrammingjargon)asourceprogram,usuallyonastepbystep,linebyline,orunitbyunitbasis.Thepriceforthisconvenienceisthattheprogramswritteninthirdgenerationlanguagesrequiremorememoryandrunmoreslowlythanthosewritteninlowerlevellanguages.上一页下一页返回TextB:ProgramDevelopmentTools4.FourthGenerationLanguagesFourthgenerationlanguagesattempttomakecommunicatingwithcomputersasmuchliketheprocessesofthinkingandtalkingtootherpeopleaspossible.Theproblemisthatthecomputerstillonlyunderstandszerosandones,soacompilerandinterpretermuststillconvertthesourcecodeintothemachinecodethatthecomputercanunderstand.FourthgenerationlanguagestypicallyconsistofEnglishlikewordsandphrases.Whentheyareimplementedonmicrocomputers,someoftheselanguagesincludegraphicdevicessuchasiconsandonscreenpushbuttonsforuseduringprogrammingandwhenrunningtheresultingapplication.上一页下一页返回TextB:ProgramDevelopmentToolsManyfourthgenerationlanguagesuseStructuredQueryLanguage(SQL)asthebasisforoperations.SQLwasdevelopedatIBMtodevelopinformationstoredinrelationaldatabases.Eventually,itwasadoptedbytheAmericanNationalStandardsInstitute(ANSI)andlaterbytheInternationalStandardsOrganization(ISO)asameansofmanagingstructured,factualdata.ManydatabasecompaniesofferanSQLtypedatabasebecausepurchasersofsuchdatabasesseektooptimizetheirinvestmentsbybuyingopendatabases,i.e.,thoseofferingthegreatestcompatibilitywithothersystems.Thismeansthattheinformationsystemsarerelativelyindependentofvendor,operatingsystem,andcomputerplatform.上一页下一页返回TextB:ProgramDevelopmentTools5.NaturalLanguagesWhereasafourthgenerationlanguageprogrammustfollowaspecificsetofrulesandsyntax,anaturallanguageprogramdoesnot.Anaturallanguage,sometimescalledafifthgenerationlanguage,isatypeofquerylanguagethatallowstheusertoenterrequeststhatresemblehumanspeech.Forexample,anSQLquerytoobtainalistofGPAsthatexceed3.5mightbewrittenasSELECTLAST_NAME,FIRST_NAMEFROMSTUDENTWHEREGPA＞3.5.AnaturallanguageversionofthatsamequerymightbewrittenorspokenasTELLMETHENAMESOFSTUDENTSWITHGPAOVER3.5.Fifthgenerationlanguagesareusedmainlyinartificialintelligenceresearch.Prolog,OPS5,andMercuryareexamplesoffifthgenerationlanguages.上一页下一页返回TextB:ProgramDevelopmentToolsWordsandExpressionscategory:n.种类，分类；范畴binarydigit:二进制位advantage:n.优势disadvantage:n.缺点；劣势tedious:adj.沉闷的；冗长乏味的Timeconsuming:adj.花费大量时间的；旷日持久的Errorprone:adj.易于出错的tedium:n.沉闷；单调乏味abbreviation:n.缩写；缩写词上一页下一页返回TextB:ProgramDevelopmentToolsmnemonics:n.助记方法，帮助记忆的公式utilityprogram:应用程序assembler:n.［计］汇编程序；汇编机isomorphic:adj.同构的；同形的spur:vt.激励，鞭策complicated:adj.难懂的，复杂的refinement:n.改进noteworthy:adj.值得注意的；显著的nonprofessional:n.外行；非专业人士routine:n.函数上一页下一页返回TextB:ProgramDevelopmentToolsstorebought:adj.现成的；店里买的sourceprogram:源程序objectprogram:目标程序implement:vt.实施，执行；实现pushbutton:按钮optimize:vt.使最优化artificialintelligencelanguage:人工智能语言querylanguage:查询语言resemble:vt.类似；与……一样version：n.版本上一页下一页返回TextB:ProgramDevelopmentToolsNotes①Assemblylanguagesdohaveseveraladvantagesovermachinelanguages.与机器语言相比较，汇编语言确实有不少优点。②InternationalBusinessMachineCorporation(IBM)：国际商业机器公司，或万国商业机器公司，简称IBM上一页下一页返回TextB:ProgramDevelopmentTools③ALGOL(ALGOrithmicLanguage):ALGOL这个名称是算法语言的简称，这种语言不是计算机制造公司为某种特定机器设计的，而是纯粹面向描述计算过程的，也就是所谓面向算法描述的。ALGOL是计算机发展史上首批产生的高级语言，其语法是用严格公式化的方法说明的。

COBOL(CommonBusinessOrientedLanguage)：面向商业的通用语言，又称为企业管理语言、数据处理语言等。COBOL是数据处理领域应用最为广泛的程序设计语言,是第一个广泛使用的高级编程语言。上一页下一页返回TextB:ProgramDevelopmentTools④DartmouthCollege:达特茅斯学院，成立于1769年，是美国第9所历史最悠久的学院，也是闻名遐迩的常春藤学院之一，坐落于美国新罕布什尔州的汉诺威(Hanover)小镇。⑤Thiswasthefirstwidespreadcomputerlanguagedesignedforandusedbynonprofessionalprogrammers.

这也是第一款为非专业程序员设计，被非专业程序员广泛使用的计算机语言。⑥Thepriceforthisconvenienceisthattheprogramswritteninthirdgenerationlanguagesrequiremorememoryandrunmoreslowlythanthosewritteninlowerlevellanguages.

这样做方便很多，但代价就是用第3代语言写的程序占据了更多的内存，比机器语言和汇编语言编写的程序运行时更慢。上一页下一页返回TextB:ProgramDevelopmentTools⑦ManyfourthgenerationlanguagesuseStructuredQueryLanguage(SQL)asthebasisforoperations.⑧AmericanNationalStandardsInstitute(ANSI):美国国家标准学InternationalStandardsOrganization(ISO):国际标准化组织⑨ExamplesoffourthgenerationlanguagesincludePROLOG,anartificialintelligencelanguagethatappliesrulestodatatoarriveatsolutions.

第4代计算机语言中就包括PROLOG,这是一种人工智能语言，把逻辑运用到程序编写中，以达到（自动）解决问题之目的。⑩…….anSQLquerytoobtainalistofGPAsthatexceed……

一个想得到GPA值大于3.5的学生姓名列表的SQL查询……上一页返回GrammarFocus一、一般现在时1.概念经常、反复发生的动作或行为及现在的某种状况。2.时间状语

always,usually,often,sometimes,everyweek(day,year,month……),onceaweek,onSundays等。3.用法（1)经常性或习惯性的动作，常与表示频度的时间状语连用。时间状语：every…,sometimes,at…,onSunday等。

(2)客观真理，客观存在，科学事实。

(3)表示格言或警句中。下一页返回GrammarFocus(4)现在时刻的状态、能力、性格、个性。二、一般过去时1.概念过去某个时间里发生的动作或状态；过去习惯性、经常性的动作、行为。2.时间状语

ago,yesterday,thedaybeforeyesterday,lastweek,last(year,night,month…),in1989,justnow,attheageof5,oneday,longlongago,onceuponatime,etc.上一页下一页返回GrammarFocus3.用法(1）在确定的过去时间里所发生的动作或存在的状态。(2）表示在过去一段时间内，经常性或习惯性的动作。三、一般将来时

1.概念表示将要发生的动作或存在的状态及打算、计划或准备做某事。2.时间状语

tomorrow,nextday(week,month,year…),soon,inafewminutes,by…,thedayaftertomorrow,etc.上一页下一页返回GrammarFocus3.用法（1)shall用于第一人称，常被will所代替。will在陈述句中用于各人称，在征求意见时常用于第二人称。WhichparagraphshallIreadfirst.Willyoubeathomeatseventhisevening?（2)begoing+不定式，表示将来。①主语的意图，即将做某事。Whatareyougoingtodotomorrow?②计划，安排要发生的事。Theplayisgoingtobeproducednextmonth.③有迹象要发生的事。上一页下一页返回GrammarFocusLookatthedarkclouds,thereisgoingtobeastorm.（3)be+不定式表将来，按计划或正式安排将发生的事。WearetodiscussthereportnextSaturday.（4)beabout+不定式，意为马上做某事。HeisabouttoleaveforBeijing.上一页下一页返回GrammarFocus四、现在完成时1.概念现在完成时用来表示之前已发生或完成的动作或状态，其结果和现在有联系。动作或状态发生在过去，但它的影响现在还存在；也可表示持续到现在的动作或状态。其构成：have(has)+过去分词。2.时间状语

recently,lately,since…for…,inthepastfewyears,etc.上一页下一页返回GrammarFocus3.用法（1）现在完成时表示到现在为止已完成或仍在持续的动作、状态，强调对现在的影响、联系,或表示经历、经验，即用过去发生的动作来说明现在的情况。（2）现在完成时用在过去已完成而其结果对现在仍有影响的动作来说明经历、经验,或表示某种感情色彩。（3）当现在完成时表示从过去某时持续到现在的动作或状态,以说明经历、经验,与for或since引导的表示一段时间的副词片语连用时,谓语动词要用be,keep,learn,live,read,serve,stay,study,teach,watch,work,write等表示持续的动词,不可使用arrive,become,begin,borrow,buy,c