专业英语听力材料.docx

专业英语听力材料.docx

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专业英语听力材料

Lecture2前17分钟

Lecture2后17分钟

Lecture3前18分钟

Lecture3后17分钟

Lecture4前18分钟

Lecture4后18分钟

Lecture5前17分钟

Lecture5后15分钟

Lecture6前19分钟

Lecture6后15分钟

Lecture7

Lecture8前15分钟

Lecture8第15—30分钟

Lecture8第30—48分钟

Lecture8第48—完

Lecture2前17分钟回首页

Thisiscomputerprogramming1fromtheUniversityofWashington.Welcomeback!

Todayinlecture2,we’llbegoingrightintothetechnicalcontentofthiscourseaswetalkaboutproblems,algorithmsandprograms.Asyoumaybeaware,programmingacomputerinvolvesagreatamountofdetail.We’llhaveplentyoftimelaterinthiscoursetogettoomanyofthosedetails.Butprogrammingalsoinvolveshigherlevelconceptsinproblemsolvingskills.I’dliketofocusonthattoday,lateronwe’llseedetailswhichwillhelpuscarryoutthesehigherlevelproblemsolvingstrategies.Sowe’lltalktodayaboutwhatproblemsmightbesolvedbycomputers,whatalgorithmsareandwhatprogramsare.We’llaboutageneralapproachtosolvingproblemswithcomputersanddiscusshowaresolutionscanbeturnedintocodethataCPUcanactuallyexecute,we’llfocustodayontheselargeideas.Tostartwith,computerprogrammingisprimarilyamatterofusingacomputertosolveaproblemthatmightbeonedefinitionofprogramming,problemsolvingthroughcomputers.Nownotallproblemsthatwerefertobythatnameineverydayusemightbeamenabletosolutionbycomputer.Problemoftrafficjamsduringrushhourforexample,probablycan’tbesolvedbywritingacprogram,andthesamegoesforproblemslikeworldpeaceorworldhunger.Heartofthisartprogrammingisbeabletorecognizewhichproblemsaresuitableforsolutions.Ingeneral,aproblemthatacomputercansolvehastobeoneforwhichyouasaprogrammercancomeupwithanalgorithm.Analgorithmisasequenceofprecisestepswhichwillleadthesolutionoftheproblem.Ifyoucan’tcomeupwiththealgorithmorsequenceofsteps,thenyoucan’tuseacomputertosolvetheproblem.Thesestepshavetobequitpreciseandtheyhavetobemechanicalinthesensethattheywillbecarriedoutbyamachine,thecomputeroncetheprogrammingisdone,ratherthanbyhumanbeing.Notionofthealgorithmisafundamentaloneanditperhapsquitedistinguishescomputersciencefromotherfieldsofscienceandengineering.Certainlyalgorithmsareusedinmanyotherfields,butnoworryexceptioncomputerscienceisthealgorithmitselfofnotion,naturenaturalcharacteristicskeepabilitiesofalgorithmsofcentralareaofstudy.Ifyoucancomeupwithanalgorithm,thenthenextstepisturnthatalgorithmintoacomputerprogram,alotofthiscoursewillbeaboutthatprocesstakingthealgorithmandturnitintoaprogramthatcanbeexecuted.Nowweexpressthesealgorithmsusingwhatwecallaprogramminglanguage,thisisaspecialnotationthatwewillbeabletotranslateintoaformthattheCPUitselfwillbeabletoexecute.OurcoursefocusesontheClanguage,therearemanyotherprogramminglanguagesthatyoumightheardseveralofthem,C++,Java,bothofwhicharequitcloselyrelatedtoCandderive（起源）tranit,othersFORTRAN,Basicyoumayhaveexperiencewith.Let’scompareprogrammingtoanotherkindofalgorithm-makeactivitythatwe’refamiliarwithfromeverydaylife,namelycooking.Solet’stakeatypicalproblem,youarehungry,youneedtoeatsomething,Fudgebrowniesoundsreallygood.Sohereistheproblem:

youwanttomakesomeFudgebrownie.OK,thatcoursebounds（跳跃）tothestatementoftheproblem,thegoal:

makeFudgebrownie,what’sthealgorithm?

Well,incookingwecallthatarecipe,arecipeissomethinglikeopentwobagsofchocolatechipsputtheminthebowl,addtwotablespoonsofflour,stir（搅拌）themtogetherandbakethemintheovenfor3hours,orwhateverthealgorithmis,youmayknowmoreaboutcookingthanIdo.OK,that’sthealgorithmknown,thestepbysteprecipethattellswhatthingstodoinwhatorder.Nowisthatquitlikeaprogram?

Well,notquit,whenwewriteaprogram,wewillbegiven（?

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）ittoaparticularcomputertoexecuteandwehavetowriteitinalanguageandnotationsthatthecomputerunderstands.Justlikearecipehastobewritteninalanguagethatthe（shouldbean‘a’here）cookunderstands.OK,soImayknowthesestepstogothroughanyingredientsbutI’vegottosaythatinEnglish,inRussian（orlan口误）orinwhateverthelanguagethecookis,you‘vegottousetherightterminology,therightoperationsanddoeverythinginexactlytherightorderbutnotendupwithFudgebrownie.OK,andIstillbehungryandIwanttosolvemyproblem.

Hereisitsprocedurethatmanypeoplefindusefulasageneralstrategyforsolvingproblemswithacomputer.Thefirststepmaybeobviousbutit’sforstating,it’stospecifywhattheproblemis.Now,althoughit’sobvious,it’softenhardtodo.Problemthatyouaregiventosolvebyclient,customer,ateacheraresometimesvague（含糊不清的）andmaytakeconsiderable（这里应该是个类似“额外的”意思的词）amountofthenextstepofprocess,analysis.Studyingtheproblem,understandwhatitreallymeans,whatreallysort,learningmoreaboutit,asmuchasyoucanfindoutaboutit,eventuallyfromthatstudy,youhopeyoucandesignanalgorithmstepbystepprocedurefordesigningtheproblem（此句有误，后面是补充。

）,designingthesolutiontotheproblems.Onceyou’vegotthealgorithmfirmlyinmind,youcanthenimplementthealgorithm,thismeanswritingaprogram.Nowit’sreallyonlyatthisstateyouneedknowledgeoftheprogramminglanguage.Soyoucandotheproblemtransactions,theanalysis,thedesignwithoutknowingwhetheryouweregoingtouseCorJava（?

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）orFORTRAN,andthenattheimplantationstagebegintranslatingthatanalysisandalgorithmintotheprogramminglanguageyourcomputerwilluse.Areyoudoneyet?

Well,itwouldbeniceifthatwasthelaststep,butit’sveryeasytomakemistakessomewhereinthisprocesssotheprogramthatyouwritehastobetested,verifiedandindoingsoyoumayfindoutitdoesn’tworkexactlyasyouplannedto.Whereisthemistake?

Wellitmightbeintheprogrammingbutyoumayfindoutitwassomeoversetdesignormaybeyouhavetogobackevenafurtherlevel,maybetheanalysiswaswrongortheproblemwasstatedwrongoryoumisunderstoodwhatthepersonwhogivesyoutheproblemwanted.Allofthesethingswillrequirereanalysis,redesigningandfixingtheproblemorhopefullyfixingtheproblemandprogramandtryagain.Itwillkeepprocessinvolvingallofthesesteps.Let’stakeasimpleproblemandapplythisproceduretoit.OK,hereisaproblem:

isagivennumberevenorodd?

Soundssimple?

Yes,itissimple.Whyisitsuchasimpleproblem?

Youmayseenotrealisticallysimpletospendtimeoninacourse.Butactually,it’snotsofarremovefromreallifeproblemsyoumightwanttosolveyouhaveapayrollsystemandyouprintcheckseveryotherweekyouhavetodeterminewhetherthisisapayrollweekornot.Whatabouttheproblemsdeterminingwhetherayearisaleapyear?

Thatisasimilarflavortoit.Beyondthat,inacourselikethis,wasslidetheyareusedtopresentinformation.Itisdifficulttocompletelysolveandpresentcomplicatedproblems.Asoneofthereasonsbytheway,thatwerecommendyoulookintothetextbookforthiscourseoranothertextbookoranotherbookonthissubjectsothatyoucanseelarger,morerealisticandmoreinterestingexamples.Butfornow,thisexamplewillserveuswellandallowsustogothroughallofthestepsrecommendedforproblemsolvingandwhenwe’redonewe’llcomeupwithacompletesolutiontotheproblemincludingcode.SowhatwouldIsaythefirststepwas?

StatetheproblemuponIhavedonethatalready.AndsoIcangoontotheanalysis,andhere,youmaystartthinkingabout,uh,what’sreallymeant?

Whatnumbersareallowed?

IsanegativenumberwhatIneedtogetananswerfor?

Whataboutafractionalnumberlike10.3.Thatevenmakesensetoaskquestionforevenoroddyouhavetoaskyourselfthisquestionoryouperhapsasktheclientorteacherwhogiveyoutheproblem.Whereisthisnumbercomefrom?

Isthisnumberthatfixesforever?

Youhavetothinkaboutthatbeforeyoucanwriteanalgorithmfortheprogram.Thenthereisamorebasicquestionaboutwhatevenoroddmean.Withyourmathematicconcepts,en,mostpeoplerememberthisfromtheirschoolmathematicsbutifyouarenotsurethiswouldbeatimetogobackandlookupandremember,remindyourselfwhatthoseconceptsare.Ihavehadevencollegelevelstudentswith12yearsmathematicsbehindthemnotbesurewhetherzeroisanevenoroddnumber.Sothispossiblehasdoubtinyourmindaboutthesethingsandtheanalysisfaceiswhatitmakessensetofigureoutwhatitreallymeant.Finally,programsaysdeterminingtheanswerbuthowdoyoureportthatanswer.Youwantthecomputertolightupabillboard（广告信息）orspeakaword.Howwastheanswertobereported?

Youhavetosightonthattoo.Thisanalysismightleadyoutorestatetheprobleminmoreprecisetermssolet’strytodothatnow.LetmerestatetheproblemI’mreallygoingtosolveasthis:

giveanintegernumber.OK,sonowI’vepaidonthekindofnumberit’sgonnabe,it’sgonnabeaninteger,anumberwithoutdecimalpoints（小数点）.Typedinfromthekeyboardsoit’snotbuiltin,itisn’tsentfromasatellite,okorsomeotherobscuremethodasitgonnabetypedin,ifitisaneven,write“even”onthescreensonowwe’llspecifyhowtheansweristobereported.Andifit’soddwe’aregonnawrite“odd”onthescreensonowwehavemuchmoreprecisedefinitionofwhattheproblemisgoingtobeandwecanproceedtothinkaboutanalgorithm.Sohereistheone,le