repetition structurepsut重复结构的阵发性室上性心动过速课件

Chapter6 TheRepetitionStructure ProgrammingwithMicrosoftVisualBasic NET SecondEdition ProgrammingwithMicrosoftVisualBasic NET SecondEdition 2 TheRepetitionStructure Looping LessonAObjectives CodetherepetitionstructureusingtheFor NextandDo LoopstatementsWritepseudocodefortherepetitionstructureCreateaflowchartfortherepetitionstructureInitializeandupdatecountersandaccumulators ProgrammingwithMicrosoftVisualBasic NET SecondEdition 3 TheRepetitionStructure Usetherepetitionstructuretorepeatedlyprocessoneormoreprograminstructionsuntilsomeconditionismet atwhichtimetherepetitionendsTherepetitionstructureisreferredtoasaloop ProgrammingwithMicrosoftVisualBasic NET SecondEdition 4 TheRepetitionStructure continued Pretestloop evaluationoccursbeforetheinstructionswithintheloopareprocessedPosttestloop evaluationoccursaftertheinstructionswithintheloopareprocessed ProgrammingwithMicrosoftVisualBasic NET SecondEdition 5 TheFor NextLoop UsetheFor Nextstatementtocodealoopthatrepeatsforaspecificnumberoftimes Figure6 2 SyntaxandexamplesoftheFor Nextstatement ProgrammingwithMicrosoftVisualBasic NET SecondEdition 6 TheFor NextLoop continued Figure6 2 SyntaxandexamplesoftheFor Nextstatement continued ProgrammingwithMicrosoftVisualBasic NET SecondEdition 7 TheFor NextLoop continued counterisanumericvariablethatkeepstrackofhowmanytimestheloopinstructionsarerepeatedstartvalue endvalue andstepvalueMustbenumericCanbepositiveornegative integerornon integerDefaultstepvalueis1 ProgrammingwithMicrosoftVisualBasic NET SecondEdition 8 TheFor NextLoop continued Figure6 4 PseudocodeandflowchartforthefirstexampleshowninFigure6 2 ProgrammingwithMicrosoftVisualBasic NET SecondEdition 9 TheFor NextLoop continued For Nextloopexamples ProgrammingwithMicrosoftVisualBasic NET SecondEdition 10 TheDo LoopStatement UnliketheFor Nextstatement theDo LoopstatementcanbeusedtocodebothapretestloopandaposttestloopTheDo LoopstatementbeginswiththeDoclauseandendswiththeLoopclause ProgrammingwithMicrosoftVisualBasic NET SecondEdition 11 TheDo LoopStatement continued Figure6 7 SyntaxandexamplesoftheDo Loopstatement ProgrammingwithMicrosoftVisualBasic NET SecondEdition 12 TheDo LoopStatement continued Figure6 7 SyntaxandexamplesoftheDo Loopstatement continued ProgrammingwithMicrosoftVisualBasic NET SecondEdition 13 TheDo LoopStatement continued Figure6 9 FlowchartsfortheexamplesshowninFigure6 7 ProgrammingwithMicrosoftVisualBasic NET SecondEdition 14 TheDo LoopStatement continued Figure6 9 FlowchartsfortheexamplesshowninFigure6 7 continued ProgrammingwithMicrosoftVisualBasic NET SecondEdition 15 UsingCountersandAccumulators Countersandaccumulatorsareusedwithinarepetitionstructuretocalculatesubtotals totals andaveragesAcounterisanumericvariableusedforcountingsomethingandistypicallyupdatedby1Anaccumulatorisanumericvariableusedforaccumulatingandisupdatedbyanamountthatvaries ProgrammingwithMicrosoftVisualBasic NET SecondEdition 16 UsingCountersandAccumulators continued Initializing assigningabeginningvaluetothecounteroraccumulatorUpdating incrementing addinganumbertothevaluestoredinthecounteroraccumulator ProgrammingwithMicrosoftVisualBasic NET SecondEdition 17 NestedRepetitionStructuresLessonBObjectives Nestrepetitionstructures ProgrammingwithMicrosoftVisualBasic NET SecondEdition 18 NestingRepetitionStructures Inanestedrepetitionstructure oneloop referredtoastheinnerloop isplacedentirelywithinanotherloop calledtheouterloopAclockusesnestedloopstokeeptrackofthetime ProgrammingwithMicrosoftVisualBasic NET SecondEdition 19 NestingRepetitionStructures continued Figure6 16 Nestedloopsusedbyaclock ProgrammingwithMicrosoftVisualBasic NET SecondEdition 20 TheGradeCalculatorApplication ProfessorArkinsneedsanapplicationthatallowshimtoassignagradetoanynumberofstudentsEachstudent sgradeisbasedonthreetestscores witheachtestworth100pointsTheapplicationshouldtotalthetestscoresandthenassigntheappropriategrade usingthetableshownonthenextslide ProgrammingwithMicrosoftVisualBasic NET SecondEdition 21 TheGradeCalculatorApplication continued ProgrammingwithMicrosoftVisualBasic NET SecondEdition 22 TheGradeCalculatorApplication continued uiAssignGradeButton sClickeventprocedureAllowsProfessorArkinstoentereachstudent stestscores andthenassigntheappropriategradeContainstwoloops onenestedwithintheotherAFor Nextstatementcontrolstheinnerloop ProgrammingwithMicrosoftVisualBasic NET SecondEdition 23 TheGradeCalculatorApplication continued uiAssignGradeButton sClickeventprocedure continued ADo LoopstatementcontrolstheouterloopTheinnerloopisapretestloopTheouterloopisaposttestloop ProgrammingwithMicrosoftVisualBasic NET SecondEdition 24 TheGradeCalculatorApplication continued Figure6 20 Samplerunoftheapplicationthatcontainstheprocedure ProgrammingwithMicrosoftVisualBasic NET SecondEdition 25 CodingtheShoppersHavenApplicationLessonCObjectives SelecttheexistingtextinatextboxPreventaformfromclosing ProgrammingwithMicrosoftVisualBasic NET SecondEdition 26 ShoppersHaven ThemanagerofShoppersHavenwantsanapplicationthatthestoreclerkscanusetocalculatethediscountedpriceofanitem usingdiscountratesfrom10 through30 inincrementsof5 Theclerkswillentertheitem soriginalpriceTheapplicationshoulddisplaythediscountratesandthediscountedpricesintheinterface ProgrammingwithMicrosoftVisualBasic NET SecondEdition 27 ShoppersHaven continued Figure6 21 UserinterfacefortheShoppersHavenapplication ProgrammingwithMicrosoftVisualBasic NET SecondEdition 28 ShoppersHaven continued Figure6 22 TOEchartfortheShoppersHavenapplication ProgrammingwithMicrosoftVisualBasic NET SecondEdition 29 ShoppersHaven continued Figure6 23 PseudocodefortheCalculatebutton sClickeventprocedure ProgrammingwithMicrosoftVisualBasic NET SecondEdition 30 ShoppersHaven continued Figure6 27 DiscountedpricesshownintheShoppersHavenapplication ProgrammingwithMicrosoftVisualBasic NET SecondEdition 31 SelectingtheExistingTextinaTextBox UsetheSelectAllmethodtoselectallofthetextcontainedinatextboxSyntax textbox SelectAll textboxisthenameofthetextboxwhosetextyouwanttoselect ProgrammingwithMicrosoftVisualBasic NET SecondEdition 32 SelectingtheExistingTextinaTextBox continued EntertheSelectAllmethodinatextboxcontrol sEntereventAtextboxcontrol sEntereventoccurswhentheusertabstothecontrol andwhentheFocusmethodisusedincodetosendthefocustothecontrolTheuiOriginalTextBoxcontrol sEntereventisresponsibleforhighlightingtheexistingtextinthecontrol ProgrammingwithMicrosoftVisualBasic NET SecondEdition 33 SelectingtheExistingTextinaTextBox continued Figure6 29 TextselectedintheShoppersHavenapplication ProgrammingwithMicrosoftVisualBasic NET SecondEdition 34 CodingtheTextChangedEventProcedure Acontrol sTextChangedeventoccurswhenthecontentsofacontrol sTextpropertychangeUsetheuiOriginalTextBox sTextChangedeventtoclearthecontentsoftheuiDiscPricesLabelwhentheuserchangestheoriginalprice ProgrammingwithMicrosoftVisualBasic NET SecondEdition 35 CodingtheShoppersForm sClosingEventProcedure Aform sClosingeventoccurswhenaformisabouttobeclosedIntheShoppersHavenapplication theClosingeventprocedureisresponsiblefor VerifyingthattheuserwantstoexittheapplicationTakinganactionbasedontheuser sresponse ProgrammingwithMicrosoftVisualBasic NET SecondEdition 36 CodingtheShoppersForm sClosingEventProcedure continued Figure6 31 PseudocodefortheShoppersForm sClosingeventprocedure ProgrammingwithMicrosoftVisualBasic NET SecondEdition 37 CodingtheShoppersForm sClosingEventProcedure continued Figure6 33 Messageboxdisplayedbytheform sClosingevent ProgrammingwithMicrosoftVisualBasic NET SecondEdition 38