SelectionStructures-SWITCHStatement-Gateway选择结构开关语句网关

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1、SwitchCaseStructuresLecture91WinterQuarterSwitchMultipleSelectionStructureAmultipleselectionstructureisusefulwhenanalgorithmcontainsaseriesofdecisionsinwhichavariableorexpressionistestedseparatelyforoneofseveralpossibleintegralvalues.Eachintegralvaluereprese

2、ntsadifferentactiontobetakeninthealgorithm.Cprovidestheswitchmultipleselectionstructuretoimplementthistypeofdecisionmaking.2WinterQuarterSwitch-CaseStructuresTheswitch-casesyntaxis:switch(integerexpressiontestvalue){casecase_1_fixed_value:action(s);casecase_

3、2_fixed_value:action(s);default:action(s);}Noteuseofcolon!3WinterQuarterSwitch-CaseStructuresTheswitchisthe"controllingexpression"Canonlybeusedwithconstantintegerexpressions.Remember,asinglecharacterisasmallpositiveinteger.Theexpressionappearsin()Thecaseisa"

4、label"Thelabelmustbefollowedbya":"Braces,{},notrequiredaroundstatements4WinterQuarterSwitch-CaseStructuresUnlikeif-elseif-elsestructures,whenthevalueinacasematchesthetestvalue,alloftheactionsintherestofthestructuretakeplace.Thisisshowninthefollowingprogramwh

5、eretheuserentersavaluethatmatchesthefirstcaseandeveryactioninthestructureisexecuted.5WinterQuarterASampleProgramtoIllustrateSwitch-CaseProblem:Writeaprogramtoasktheusertoenterhis/herlettergradeandthenrespondwithanappropriatemessageregardinghis/heracademicsta

6、tus.6WinterQuarterASampleProgramtoIllustrateSwitch-CaseAlgorithm:1.Setuptheenvironment2.Promptusertoenterhis/herlettergrade3.Getuser’sresponse4.IfgradeisaorAsay“GoodJob”andgoto95.IfgradeisborBsay“Prettygood”andgoto96.IfgradeiscorCsay“Bettergettowork”andgoto9

7、7IfgradeisdorDsay“Youareintrouble”andgoto98.Say“Youarefailing”9.Terminateprogram7WinterQuarterASampleProgramtoIllustrateSwitch-Case/*Thisprogramassociatesalettergradewithamessageappropriatetothescore.*/#includevoidmain(){chargrade;printf("Enteryourc

8、urrentlettergrade");grade=getchar();8WinterQuarterASampleProgramtoIllustrateSwitch-Caseswitch(grade){case('a'):case('A'):printf("GoodJob!");case('b'):case('B'):printf("Prettygood.");9Winte