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1、Unit3ComputerLanguageandProgrammingSectionAProgrammingLanguageI.IntroductionProgramminglanguages,incomputerscience,aretheartificiallanguagesusedtowriteasequenceofinstructions(acomputerprogram)thatcanberunbyacomputer.Similartonaturallanguages,suchasEnglish,programminglanguageshaveavocabu
2、lary,grammar,andsyntax.However,naturallanguagesarenotsuitedforprogrammingcomputersbecausetheyareambiguous,meaningthattheirvocabularyandgrammaticalstructuremaybeinterpretedinmultipleways.Thelanguagesusedtoprogramcomputersmusthavesimplelogicalstructures,andtherulesfortheirgrammar,spelling
3、,andpunctuationmustbeprecise.Programminglanguagesvarygreatlyintheirsophisticationandintheirdegreeofversatility.Someprogramminglanguagesarewrittentoaddress（处理）aparticularkindofcomputingproblemorforuseonaparticularmodelofcomputersystem・Forinstance,programminglanguagessuchasFORTRAN1andCOBO
4、L2werewrittentosolvecertaingeneraltypesofprogrammingproblems一FORTRANforscientificapplications,andCOBOLforbusinessapplications.Althoughtheselanguagesweredesigntoaddressspecificcategoriesofcomputerproblems,theyarehighlyportable（可移植），meaningthattheymaybeusedtoprogrammanytypesofcomputers.Ot
5、herlanguages,suchasmachinelanguages,aredesignedtobeusedbyonespecificmodelofcomputersystem,orevenbyonespecificcomputerincertainresearchapplications.Themostcommonlyusedprogramminglanguagesarehighlyportableandcanbeusedtoeffectivelysolvediversetypesofcomputingproblems.LanguageslikeC,PASCALa
6、ndBASICfallinto（属于）thiscategory.I.LanguageTypesProgramminglanguagescanbeclassifiedaseitherlow-levellanguagesorhigh-levellanguages.Low-levelprogramminglanguages,ormachinelanguages,arethemostbasictypeofprogramminglanguagesandcanbeunderstooddirectlybyacomputer.Machinelanguagesdifferdependi
7、ngonthemanufacturerandmodelofcomputer.High-levellanguagesareprogramminglanguagesthatmustfirstbetranslatedintoamachinelanguagebeforetheycanbeunderstoodandprocessedbyacomputer.Examplesofhigh-levellanguagesareC,C++6,PASCAL,andFORTRAN.Assemblylanguagesareintermediatelanguagesthatar
