英文文献翻译计算机程序3

1、姓名：刘峻霖班级：通信143班学号：08ComputerLanguageandProgrammingI.IntroductionProgramminglanguages,incomputerscience,aretheartificiallanguagesusedtowriteasequenceofinstructions(acomputerprogram)thatcanberunbyacomputer.Similartonaturallanguages,suchasEnglish,programminglanguageshaveavocabulary,grammar,andsyntax.Ho

2、wever,naturallanguagesarenotsuitedforprogrammingcomputersbecausetheyareambiguous,meaningthattheirvocabularyandgrammaticalstructuremaybeinterpretedinmultipleways.Thelanguagesusedtoprogramcomputersmusthavesimplelogicalstructures,andtherulesfortheirgrammar,spelling,andpunctuationmustbeprecise.Programmi

3、nglanguagesvarygreatlyintheirsophisticationandintheirdegreeofversatility.Someprogramminglanguagesarewrittentoaddressaparticularkindofcomputingproblemorforuseonaparticularmodelofcomputersystem.Forinstance,programminglanguagessuchasFORTRANandCOBOLwerewrittentosolvecertaingeneraltypesofprogrammingprobl

4、emsFORTRANforscientificapplications,andCOBOLforbusinessapplications.Althoughtheselanguagesweredesignedtoaddressspecificcategoriesofcomputerproblems,theyarehighlyportable,meaningthattheymaybeusedtoprogrammanytypesofcomputers.Otherlanguages,suchasmachinelanguages,aredesignedtobeusedbyonespecificmodelo

5、fcomputersystem,orevenbyonespecificcomputerincertainresearchapplications.Themostcommonlyusedprogramminglanguagesarehighlyportableandcanbeusedtoeffectivelysolvediversetypesofcomputingproblems.LanguageslikeC,PASCALandBASICfallintothiscategory.II.LanguageTypesProgramminglanguagescanbeclassifiedaseither

6、low-levellanguagesorhigh-levellanguages.Low-levelprogramminglanguages,ormachinelanguages,arethemostbasictypeofprogramminglanguagesandcanbeunderstooddirectlybyacomputer.Machinelanguagesdifferdependingonthemanufacturerandmodelofcomputer.High-levellanguagesareprogramminglanguagesthatmustfirstbetranslat

7、edintoamachinelanguagebeforetheycanbeunderstoodandprocessedbyacomputer.Examplesofhigh-levellanguagesareC,C+,PASCAL,andFORTRAN.Assemblylanguagesareintermediatelanguagesthatareveryclosetomachinelanguagesanddonothavetheleveloflinguisticsophisticationexhibitedbyotherhigh-levellanguages,butmuststillbetra

8、nslatedintomachinelanguage.1.MachineLanguagesInmachinelanguages,instructionsarewrittenassequencesof1sand0s,calledbits,thatacomputercanunderstanddirectly.Aninstructioninmachinelanguagegenerallytellsthecomputerfourthings:(1)wheretofindoneortwonumbersorsimplepiecesofdatainthemaincomputermemory(RandomAc

9、cessMemory,orRAM),(2)asimpleoperationtoperform,suchasaddingthetwonumberstogether,(3)whereinthemainmemorytoputtheresultofthissimpleoperation,and(4)wheretofindthenextinstructiontoperform.Whileallexecutableprogramsareeventuallyreadbythecomputerinmachinelanguage,theyarenotallprogrammedinmachinelanguage.

10、Itisextremelydifficulttoprogramdirectlyinmachinelanguagebecausetheinstructionsaresequencesof1sand0s.Atypicalinstructioninamachinelanguagemightread1001011001011andmeanaddthecontentsofstorageregisterAtothecontentsofstorageregisterB.2.High-LevelLanguagesHigh-levellanguagesarerelativelysophisticatedsets

11、ofstatementsutilizingwordsandsyntaxfromhumanlanguage.Theyaremoresimilartonormalhumanlanguagesthanassemblyormachinelanguagesandarethereforeeasiertouseforwritingcomplicatedprograms.Theseprogramminglanguagesallowlargerandmorecomplicatedprogramstobedevelopedfaster.However,high-levellanguagesmustbetransl

12、atedintomachinelanguagebyanotherprogramcalledacompilerbeforeacomputercanunderstandthem.Forthisreason,programswritteninahigh-levellanguagemaytakelongertoexecuteanduseupmorememorythanprogramswritteninanassemblylanguage.3.AssemblyLanguagesComputerprogrammersuseassemblylanguagestomakemachine-languagepro

13、gramseasiertowrite.Inanassemblylanguage,eachstatementcorrespondsroughlytoonemachinelanguageinstruction.Anassemblylanguagestatementiscomposedwiththeaidofeasytoremembercommands.ThecommandtoaddthecontentsofthestorageregisterAtothecontentsofstorageregisterBmightbewrittenADDB,Ainatypicalassemblylanguages

14、tatement.Assemblylanguagessharecertainfeatureswithmachinelanguages.Forinstance,itispossibletomanipulatespecificbitsinbothassemblyandmachinelanguages.Programmersuseassemblylanguageswhenitisimportanttominimizethetimeittakestorunaprogram,becausethetranslationfromassemblylanguagetomachinelanguageisrelat

15、ivelysimple.Assemblylanguagesarealsousedwhensomepartofthecomputerhastobecontrolleddirectly,suchasindividualdotsonamonitorortheflowofindividualcharacterstoaprinter.III.ClassificationofHigh-LevelLanguagesHigh-levellanguagesarecommonlyclassifiedasprocedure-oriented,functional,object-oriented,orlogiclan

16、guages.Themostcommonhigh-levellanguagestodayareprocedure-orientedlanguages.Intheselanguages,oneormorerelatedblocksofstatementsthatperformsomecompletefunctionaregroupedtogetherintoaprogrammodule,orprocedure,andgivenanamesuchas“procedureA.”Ifthesamesequenceofoperationsisneededelsewhereintheprogram,asi

17、mplestatementcanbeusedtoreferbacktotheprocedure.Inessence,aprocedureisjustamini-program.Alargeprogramcanbeconstructedbygroupingtogetherproceduresthatperformdifferenttasks.Procedurallanguagesallowprogramstobeshorterandeasierforthecomputertoread,buttheyrequiretheprogrammertodesigneachproceduretobegene

18、ralenoughtobeusedindifferentsituations.Functionallanguagestreatprocedureslikemathematicalfunctionsandallowthemtobeprocessedlikeanyotherdatainaprogram.Thisallowsamuchhigherandmorerigorouslevelofprogramconstruction.Functionallanguagesalsoallowvariablessymbolsfordatathatcanbespecifiedandchangedbytheuse

19、rastheprogramisrunningtobegivenvaluesonlyonce.Thissimplifiesprogrammingbyreducingtheneedtobeconcernedwiththeexactorderofstatementexecution,sinceavariabledoesnothavetoberedeclared,orrestated,eachtimeitisusedinaprogramstatement.Manyoftheideasfromfunctionallanguageshavebecomekeypartsofmanymodernprocedu

20、rallanguages.Object-orientedlanguagesareoutgrowthsoffunctionallanguages.Inobject-orientedlanguages,thecodeusedtowritetheprogramandthedataprocessedbytheprogramaregroupedtogetherintounitscalledobjects.Objectsarefurthergroupedintoclasses,whichdefinetheattributesobjectsmusthave.Asimpleexampleofaclassist

21、heclassBook.ObjectswithinthisclassmightbeNovelandShortStory.Objectsalsohavecertainfunctionsassociatedwiththem,calledmethods.Thecomputeraccessesanobjectthroughtheuseofoneoftheobjectsmethods.Themethodperformssomeactiontothedataintheobjectandreturnsthisvaluetothecomputer.Classesofobjectscanalsobefurthe

22、rgroupedintohierarchies,inwhichobjectsofoneclasscaninheritmethodsfromanotherclass.Thestructureprovidedinobject-orientedlanguagesmakesthemveryusefulforcomplicatedprogrammingtasks.Logiclanguagesuselogicastheirmathematicalbase.Alogicprogramconsistsofsetsoffactsandif-thenrules,whichspecifyhowonesetoffac

23、tsmaybededucedfromothers,forexample:IfthestatementXistrue,thenthestatementYisfalse.Intheexecutionofsuchaprogram,aninputstatementcanbelogicallydeducedfromotherstatementsintheprogram.Manyartificialintelligenceprogramsarewritteninsuchlanguages.IV.LanguageStructureandComponentsProgramminglanguagesusespe

24、cifictypesofstatements,orinstructions,toprovidefunctionalstructuretotheprogram.Astatementinaprogramisabasicsentencethatexpressesasimpleideaitspurposeistogivethecomputerabasicinstruction.Statementsdefinethetypesofdataallowed,howdataaretobemanipulated,andthewaysthatproceduresandfunctionswork.Programme

25、rsusestatementstomanipulatecommoncomponentsofprogramminglanguages,suchasvariablesandmacros(mini-programswithinaprogram).Statementsknownasdatadeclarationsgivenamesandpropertiestoelementsofaprogramcalledvariables.Variablescanbeassigneddifferentvalueswithintheprogram.Thepropertiesvariablescanhavearecal

26、ledtypes,andtheyincludesuchthingsaswhatpossiblevaluesmightbesavedinthevariables,howmuchnumericalaccuracyistobeusedinthevalues,andhowonevariablemayrepresentacollectionofsimplervaluesinanorganizedfashion,suchasatableorarray.Inmanyprogramminglanguages,akeydatatypeisapointer.Variablesthatarepointersdono

27、tthemselveshavevalues;instead,theyhaveinformationthatthecomputercanusetolocatesomeothervariablethatis,theypointtoanothervariable.Anexpressionisapieceofastatementthatdescribesaseriesofcomputationstobeperformedonsomeoftheprogramsvariables,suchasX+Y/Z,inwhichthevariablesareX,Y,andZandthecomputationsare

28、additionanddivision.Anassignmentstatementassignsavariableavaluederivedfromsomeexpression,whileconditionalstatementsspecifyexpressionstobetestedandthenusedtoselectwhichotherstatementsshouldbeexecutednext.Procedureandfunctionstatementsdefinecertainblocksofcodeasproceduresorfunctionsthatcanthenbereturn

29、edtolaterintheprogram.Thesestatementsalsodefinethekindsofvariablesandparameterstheprogrammercanchooseandthetypeofvaluethatthecodewillreturnwhenanexpressionaccessestheprocedureorfunction.Manyprogramminglanguagesalsopermitminitranslationprogramscalledmacros.Macrostranslatesegmentsofcodethathavebeenwri

30、tteninalanguagestructuredefinedbytheprogrammerintostatementsthattheprogramminglanguageunderstands.V.HistoryProgramminglanguagesdatebackalmosttotheinventionofthedigitalcomputerinthe1940s.Thefirstassemblylanguagesemergedinthelate1950swiththeintroductionofcommercialcomputers.Thefirstprocedurallanguages

31、weredevelopedinthelate1950stoearly1960s:FORTRAN,createdbyJohnBackus,andthenCOBOL,createdbyGraceHopperThefirstfunctionallanguagewasLISP,writtenbyJohnMcCarthy4inthelate1950s.Althoughheavilyupdated,allthreelanguagesarestillwidelyusedtoday.Inthelate1960s,thefirstobject-orientedlanguages,suchasSIMULA,eme

32、rged.Logiclanguagesbecamewellknowninthemid1970swiththeintroductionofPROLOG6,alanguageusedtoprogramartificialintelligencesoftware.Duringthe1970s,procedurallanguagescontinuedtodevelopwithALGOL,BASIC,PASCAL,C,andAdaSMALLTALKwasahighlyinfluentialobject-orientedlanguagethatledtothemergingofobject-oriente

33、dandprocedurallanguagesinC+andmorerecentlyinJAVA10.Althoughpurelogiclanguageshavedeclinedinpopularity,variationshavebecomevitallyimportantintheformofrelationallanguagesformoderndatabases,suchasSQL.计算机程序一、序言计算机程序是指导计算机执行某个功能或功能组合的一套指令。要使指令获取执行，计算机必定执行程序，也就是说，计算机要读取程序，尔后按正确的序次推行程序中编码的步骤，直至程序结束。一个程序可多次

34、执行，而且每次用户输给计算机的选项和数据不同样，就有可能获取不同样的结果。程序可分为两大类：应用程序和操作系统。应用程序直接为用户执行某项功能，如字办理或玩游戏。操作系统管理计算机和与之相连的各种资源和设备，如随机接见储藏器、硬盘驱动器、监察器、键盘、打印机和调制解调器，以便使其他程序能够使用它们。操作系统的例子包括：DOS、Windows95、OS/2和UNIX。二、程序开发软件设计者经过特其他应用程序来开发新程序，这些应用程序常被称作合用程序或开发程序。程序员使用称作文本编写器的另一种程序，来以称作编程语言的特别标记编写新程序。使用文本编写器，程序员创办一个文本文件，这个文本文件是一个有序

35、指令表，也称为程序源文件。组成程序源文件的单个指令被称为源代码。在这个时候，一种特其他应用程序将源代码翻译成机器语言或目标代码操作系统将认作真程序并能够执行的一种格式。将源代码翻译成目标代码的应用程序有3种：编译器、讲解器和汇编程序。这3种应用程序在不同样种类的编程语言上执行不同样的操作，但是它们都起到将编程语言翻译成机器语言的同样目的。编译器将使用FORTRAN、C和Pascal等高级编程语言编写的文本文件一次性从源代码翻译成目标代码。这不同样于BASIC等讲解执行的语言所采用的方式，在讲解执行的语言中程序是随着每条指令的执行而逐个语句地翻译成目标代码的。讲解执行的语言的优点是，它们能够马上

36、开始执行程序，而不需要等到所有的源代码都获取编译。对程序的更正也能够相当快地作出，而无需等到重新编译整个程序。讲解执行的语言的缺点是，它们执行起来慢，由于每次运行程序，都必定对整个程序一次一条指令地翻译。另一方面，编译执行的语言只编译一次，因此计算机执行起来要比讲解执行的语言快得多。由于这个原因，编译执行的语言更常使用，而且在专业和科学领域几乎总是获取采用。另一种翻译器是汇编程序，它被用于以汇编语言编写的程序或程序组成部分。汇编语言也是一种编程语言，但它比其他种类的高级语言更凑近于机器语言。在汇编语言中，一条语句平时能够翻译成机器语言的一条指令。今天，汇编语言很少用来编写整个程序，而是最经常地

37、采用于程序员需要直接控制计算机某个方面功能的场合。程序经常被编写作一套较小的程序段，每段代表整个应用程序的某个方面。各段独立编译此后，一种被称为连接程序的程序将所有编译好的程序段组合成一个能够执行的完满程序。程序极稀有第一次能够正确运行的，因此一种被称为调试程序的程序常被用来帮助查找被称为程序错误的问题。调试程序平时在运行的程序中检测到一个事件，并向程序员指出事件在程序代码中的起源。近来出现的编程系统，如Java，采用多种方法相结合的方式创办和执行程序。编译器取来Java源程序，并将其翻译成中间形式。这样的中间程序随后经过因特网传达给计算机，而这些计算机里的讲解程序接下来将中间程序作为应用程序

38、来执行。三、程序元素大多数程序可是由少许几种步骤组成，这些步骤在整个程序中在不同样的上下文和以不同样的组合方式多次重复。最常有的步骤执行某种计算，尔后依照程序员指定的顺序，进入程序的下一个步骤。程序经常需要多次重复不长的一系列步骤，比方，阅读游戏得分表，从中找出最高得分。这种重复的代码序列称为循环。计算机所拥有的使其这样适用的能力之一，就是它们能够作出条件判断，并依照正在办理的数据的值执行不同样的指令。if-then-else（若是则否则）语句经过测试某个数据段，尔后依照结果从两个指令序列中选出一个，来执行这个功能。这些选择对象中的指令之一可能是一个goto语句，用以指引计算机从程序的另一个部

39、分选择下一条指令。比方，一个程序可能比较两个数，并依照比较的结果而分支到程序的另一个部分：Ifxisgreaterthanythengotoinstruction#10elsecontinue程序经常不仅一次地使用特定的一系列步骤。这样的一系列步骤能够组合成一个子例程，而子例程依照需要可在主程序的不同样部分进行调用或接见。每次调用一个子例程，计算机都会记住它自己在该调用发生时处在程序的那个地址，以便在运行完该子例程后还能够够回到那处。在每次调用从前，程序能够指定子例程使用不同样的数据，从而做到一个通用性很强的代码段只编写一次，而被以多种方式使用。大多数程序使用几种不同样的子例程。其中最常用的是函数、过程、库程序、系统程序以及设备驱动程序。函数是一种短子例程，用来计算某个值，如角的计算，而该值计算机仅用一条基本指令无法计算。过程执行的是复杂一些的功能，如给一组名称排序。库程序是为好多不同样的程序使用而编写的子例程。系统程序和库程序相似，但实质上用于操作系统。它们为应用程序供应某种服务，如打印一行文字。设备驱动程序是一种系统程序，它们加到操作系统中，以使计算机能够与扫描仪、调制解调器或打印机等新设备进行通信。设备驱动程序经常拥有能够直接作为应用程序执行的特色