程序设计导论.pptx

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1、1indexReviewingcomputerhardwareIntroductionofprogramminglanguageAlgorithmsStructuredprogrammingThesoftwaredevelopmentprogress第1页/共48页2Computer HardwareComputersareconstructedfromphysicalcomponentsreferredtoashardwareHardwarefacilitatesthestorageandprocessingofdataunderthedirectionofafilesystemComput

2、erhardwaredoesnotstoredatausingthesamesymbolsthathumansdo第2页/共48页3Bits and BytesThesmallestandmostbasicdataiteminacomputerisabitOpenorclosedswitch0or1Thegroupingof8bitstoformalargerunitisreferredtoasabyteCanrepresentanyoneof256distinctpatternsThecollectionsofpatternsconsistingof0sand1susedtorepresen

3、tletters,singledigits,andothersinglecharactersarecalledcharacter codescomputer hardware第3页/共48页4Componentscomputer hardware第4页/共48页5Main Memory Unit(RAM)StoresdataandinstructionsassequenceofbytesAprogrammustresideinmainmemoryifitistooperateonthecomputerCombines1ormorebytesintoasingleunit,referredtoa

4、sawordConstructedasrandomaccessmemory,orRAMEverysectionofmemorycanbeaccessedrandomlyasquicklyasanyothersectionVolatile:dataislostwhenpoweristurnedoffSizeisusuallyspecifiedinbytes(MBorGB)computer hardware第5页/共48页6Central Processing Unit(CPU)Control unit:directsandmonitorstheoveralloperationofthecompu

5、terKeepstrackofwherethenextinstructionresidesIssuesthesignalsneededtobothreaddatafromandwritedatatootherunitsinthesystemExecutesallinstructionsArithmetic and Logic Unit(ALU):performsallofthecomputations,suchasaddition,subtraction,comparisons,andsoon,CPUsareconstructedasasinglemicrochip,whichisreferr

6、edtoasamicroprocessorcomputer hardware第6页/共48页7Input/Output UnitnThe input/output(I/O)unit provides access to the computer,allowing it to input and output datanIt is the interface to which peripheral(外围的)devices,such as keyboards,console screens,and printers,are attachedcomputer hardware第7页/共48页8Sec

7、ondary StoragenUsed as permanent storage for programs and dataMagnetic tape,magnetic disks,and CD-ROMsnDirect access storage device(DASD):allows a computer to read or write any one file or program independent of its position on the storage mediumMagnetic hard disk consists of rigid platters that spi

8、n together on a common spindleInitially,the most common magnetic disk storage device was the removable floppy diskcomputer hardware第8页/共48页9Magnetic Hard Disk扇区柱面道computer hardware第9页/共48页10Programming LanguagesComputer program:dataandinstructionsusedtooperateacomputerandproduceaspecificresultAprogr

9、amorsetofprogramsiscalledsoftwareProgramming:writinginstructionsinalanguagethatthecomputercanrespondtoandthatotherprogrammerscanunderstandProgramming language:setofinstructionsthatcanbeusedtoconstructaprogram第10页/共48页11Machine LanguageExecutable program:programthatcanoperateacomputerExecutableprogra

10、msarewrittenwithbinarynumbers,whichisacomputersinternallanguage(machine language)Anexampleofasimplemachinelanguageprogramcontainingtwoinstructionsis:1100000000000000000100000000001011110000000000000010000000000011Opcodeisshortforoperationcode;tellsthecomputertheoperationtobeperformedProgramming Lang

11、uages第11页/共48页12Assembly LanguagenAssembly language:uses the substitution of word-like symbols for the opcodes,and decimal numbers and labels for memory addresses LOAD firstADD secondMUL factorSTORE answer load R1,R0 load R2,new_number ADD R2,R1 jmp addressProgramming Languages第12页/共48页13Assembly La

12、nguage(continued)Programming Languages第13页/共48页14The level of languages11000000,00000000,00010000,00000010opcodeMachine languageAssembly languageADD op1 op2Language specificationrate=rate+1;High level languagecompileruse instructions that are directly tied to one type of computer.Source codeObject c

13、odeProgramming Languages第14页/共48页15High-to-Low Level Languages(compile&link)Programming Languages第15页/共48页16Data pipe line1+ratedep*R_step1 depositrateoutputrateR_step1depositoutputR_step1registersControlunitWhat is a program(physically)Asetofinstructionsthatcanmakethecomputerrunchronologically.rate

14、=rate+1;result=rate*deposit a program第16页/共48页17Program is a white box for data processing(logically)a program第17页/共48页18Coding an algorithm:construct a white box step by stepAlgorithms第18页/共48页19Algorithms (arithmetic progression)Algorithms第19页/共48页20AlgorithmsAlgorithm:specificstepsrequiredtoprodu

15、ceadesiredresultSet n equal to 100Set a equal to 1Set b equal to 100Calculate sum=n(a+b)/2Display the sumWhenEnglishphrasesareusedtodescribeanalgorithm,thedescriptioniscalledpseudocodeInput the three numbers into the computerCalculate the average by adding the numbers and dividing the sum by threeDi

16、splay the averageAlgorithms第20页/共48页21Algorithms and flowchartAformulaorsetofstepsforsolvingaparticularproblem.Tobeanalgorithm,thesetofrulesmustbeunambiguousandhaveaclearstoppingpoint.Algorithmscanbeexpressedinanylanguage,fromnaturallanguageslikeEnglishorChinese.Algorithms第21页/共48页22flow chartAflowc

17、hartisanorganizedcombinationofshapes,lines,andtextthatgraphicallyillustratesaprocessorstructure.Algorithms第22页/共48页23Flowchart SymbolsAlgorithms第23页/共48页24Flowchart for calculating the average of three numbersAlgorithms第24页/共48页25structured programming Atechniquefororganizingandcodingcomputerprogram

18、s:ahierarchyofmodulesisused,eachhavingasingleentryandasingleexitpoint,controlispasseddownwardthroughthestructurewithoutunconditionalbranchestohigherlevelsofthestructure.structured programming第25页/共48页26A module must accept data,process the data,and produce a resultstructured programming第26页/共48页27St

19、ructured programmingA well-designed program is built using modulesstructured programming第27页/共48页28First-level structure diagramstructured programming第28页/共48页29Second-level refinement structure diagramstructured programming第29页/共48页30The Software Development ProcessPhase I:Specify the programs requ

20、irementsPhase II:Design and development Step 1:Analyze the problem Step 2:Select an overall solution algorithm Step 3:Write the program Step 4:Test and correct the programPhase III:DocumentationPhase IV:Maintenance第30页/共48页31Phase I:Specify the Programs RequirementsItisimpossibletoconstructasuccessf

21、ulprogramforaproblemthatisnotfullyunderstood.Software Development process第31页/共48页32Phase II:Design and DevelopmentStep1:Analyzetheproblem.Youmustunderstand:TheoutputsthatmustbeproducedTheinputdatarequiredtocreatethedesiredoutputsTheformulasrelatingtheinputstotheoutputsStep2:Selectanoverallsolutiona

22、lgorithmSoftware Development process第32页/共48页33Phase II:Design and Development(continued)Software Development process第33页/共48页34Phase II:Design and Development(continued)Forlargerprogramsyouwillhavetorefinetheinitialalgorithmandorganizeitintosmalleralgorithms,withspecificationsforhowthesesmalleralgo

23、rithmswillinterfacewitheachotherFirst-level structure diagram foranalgorithmisthefirstattemptatastructureforasolutionalgorithmTop-down algorithm development startsatthetopmostlevelandproceedstodevelopmoreandmoredetailedalgorithmsasitproceedstothefinalsetofalgorithmsSoftware Development process第34页/共

24、48页35Phase II:Design and Development(continued)Software Development process第35页/共48页36Phase II:Design and Development(continued)Software Development process第36页/共48页37Phase II:Design and Development(continued)Thesooneryoustartprogramminganapplication,thelongeritusuallytakestodebugandcomplete.Softwar

25、e Development process第37页/共48页38Phase II:Design and Development(continued)Step3:Writetheprogram(orcodethealgorithm)Sequence structuredefinestheorderinwhichinstructionsareexecutedbytheprogramSelection structureprovidesthecapabilitytomakeachoicebetweendifferentinstructions,dependingontheresultofsomeco

26、nditionRepetition structure,alsocalledlooping oriteration,providestheabilityforthesameoperationtoberepeatedbasedonthevalueofaconditionInvocation Software Development process第38页/共48页39Phase II:Design and Development(continued)Step4:TestandcorrecttheprogramAprogramerroriscalledabugTestingattemptstoen

27、surethataprogramworkscorrectlyandproducesmeaningfulresultsIfyoufindanerror,initiatedebugging:locating,correcting,andverifyingthecorrectionDevelopasetoftestdatathatdetermineswhethertheprogramgivescorrectanswersThetestsshouldexamineeverypossiblesituationunderwhichaprogramwillbeusedSoftware Development

28、 process第39页/共48页40第40页/共48页41Phase III:DocumentationSixdocumentsforeveryproblemsolution:1.Therequirementsstatement2.Adescriptionofthealgorithmsthatwerecoded3.Commentswithinthecodeitself4.Adescriptionofmodificationandchangesmadeovertime5.Sampletestruns,whichincludetheinputsusedforeachrunandtheoutput

29、obtainedfromtherun6.Ausersmanual,whichisadetailedexplanationofhowtousetheprogramSoftware Development process第41页/共48页42Case Study:circumference of circleVoidmain()Statements;compoundstatements;/commentsSoftware Development process第42页/共48页43Phase IV:MaintenanceHoweasilyaprogramcanbemaintained(correc

30、ted,modified,orenhanced)isrelatedtotheeasewithwhichtheprogramcanbereadandunderstoodSoftware Development process第43页/共48页44BackupMakingandkeepingbackupcopiesofyourworkwhenwritingaprogramiscriticalNotpartoftheformalsoftwaredevelopmentprocessBackupisunimportantifyoudontmindstartingalloveragainManyorgan

31、izationskeepatleastonebackuponsitewhereitcanbeeasilyretrieved,andanotherbackupcopyeitherinafireproofsafeorataremotelocationSoftware Development process第44页/共48页45What is a Programming Language for (conclusion)ProgrammingisanexplanatoryactivityToyourself,nowandinthefuture.Towhoeverhastoreadyourcode.T

32、othecompiler,whichhastomakeitrun.ExplanationsrequirelanguageTostateclearlywhatisgoingon.Tocommunicateideasoverspaceandtime.第45页/共48页46How to make a nice programAnalysistheproblemCorrectalgorithmNicestructureCodingwithCommentsDebuggingdocumentation第46页/共48页47The assignment:Finishandhandinpersonalwebpage(10.8)ReadthematerialrecommendedinChapterone.Includetheexercises.第47页/共48页48感谢您的观看！第48页/共48页