Chart(流程图)is.ppt

Ch5SelectionStatements,ProgrammingConstruct,1）Wedividethebasicprogrammingconstructintothreetypes:SequentialStructure、SelectionStructureandLoopStructure.2）FlowChart(流程图)：isagraphicalrepresentationinwhichspecificsymbolsandnecessarylettersareusedtodescribethesteps.3）Theflowchartaboutthethreebasicprogrammingconstructisasfollows：,Sequentialstructure,SelectionStructure,SelectionStructure,1、relationoperatorandrelationexpression,2、logicaloperatorsandlogicalexpression,3、ifstatements,4、switchstatements,5、examples,ChapterOutline,Threeforms：,（1）if（expression）statements（2）if（expression）statements1elsestatements2（3）if（expression1）statements1elseif(expression2)statements2elseif(expression3)statements3elseif（expressionm）statementsmelsestatementsn,ex,ex,ex,BriefSummary,Forme1：if（expression）statements,F(0),T(not0),ex：if(xy)printf(“%d”,x);Firstly,solvetheexpression.Ifthevalueoftheexpressionisnotzero，thenthecorrespondingststementsequenceisexcuted.Ifnoneoftheexpressionisfalse,thenexcutethestatementsafterifderectly.,example,ex：if(xy)printf(“%d”,x);elseprintf(“%d”,y);,Form2：if（expression）statements1elsestatements2,example,ex：if(number500)cost=0.15;elseif(number300)cost=0.10;elseif(number100)cost=0.075;elseif(number50)cost=0.05;elsecost=0;,Form3：nested-ifstatements,example,（1）Theexpressionofthreeformsbehindif-statementsalwaysislogicalorrelationexpression.,DCLofthreeif-statementsforms：,（2）Inform2andforme3，thereisasemicoloninfrontofelse,alsointheendofallstatements.,（3）Behindiforelse,itmayincludeonlyoneoperatestatements,alsoincludemanystatements,butshouldbedrawedtogetherwithbrace.(),Ex:#includemain()intx,y;scanf(“%d,%d”,CompileError!,ex：if(a+ba,Notice：Thebrace(“”)souterfaceneednotsemicolon。Becauseinthebrace()thereisafullcompoundstatement.,originalprogram:main()floata,b,t;scanf(“%f,%f”,ex1：Inputtwerealnumbers，pleaseoutputtherenumbersaccordingtotheorderoflittletobig.,Needthreefloatvariables:a,b,t,ex2：Inputthreerealnumbers，pleaseoutputtherenumbersaccordingtotheorderoflittletobig.,originalprogram:main()floata,b,c,t;scanf(“%f,%f,%f”,Return,#includemain()inta,b;printf(Enterintegera:);scanf(%d,ex3：Iputtwonumbers,decidethemtobeequallyornot.,Result：Enterintegera:12Enterintegerb:12a=b,Result：Enterintegera:12Enterintegerb:9a!=b,Return,Generalform：expression1？expression2：expression3,Conditionoperatorcommandsthreeoperateobjects,itisaoperatoralonelyinClanguage.,ex：max=(ab)?a:b;,Equalto：if(ab)max=a;elsemax=b;,Conditionoperator,DCL：（1）Executionorder：Firstly,solvetheexpression1，,Ifthevalueisture,thensolvetheexpression2,thismomenthereisthevalueofwholeexpressions.,Ifthevalueisfalse,thensolvetheexpression3,thismomenthereisthevalueofwholeexpressions.,ex：max=(ab)?a:b;,Ifa=3,b=4;,max=4；,Ifa=6，b=4;,max=6；,（2）Conditionoperatorovermatchassignedoperator,butunderrelationandarithmeticoperator.,（3）Conditionoperatorscombineddirecionisfromrighttoleft.,ex1：max=(ab)?a:b;,max=ab?a:b;,ex2：max=ab?a:b+1;,max=ab?a:(b+1);,ex3：max=ab?a:cd?c:d；,max=ab?a:（cd?c:d）;,Supposea=1,b=2,c=3,d=4,（4）Conditionoperatorcanntreplceordinaryif-statements,onlywhentheembedstatementsinitisassignedstatements(andtwobranchesassigntothesamevariable).,ex：if(ab)printf(“%d”,a);elseprintf(“%d”,b);,printf(“%d”,ab?a:b);,（5）Thetypeofexpression1andexpression2canbesame,alsobedifferent.,ex：intx;x?a:b;,ex：xy?1:1.5;,Ex5:Inputaletter，iudgeitisacapitalletterornot，ifis，thenchangeittolower-caseletter；ifnot，thennothingchanged。Finally,outputthisletter。,main()charch;scanf(“%c“,Return,main()floatx;inty;scanf(“%f”,Return,Algorithm2：inputxifx0y=1outputy,Algorithm3：inputxifx=0)if(x0)y=1;elsey=0;elsey=-1;,p3：modifyto：y=-1;if(x!=0)if(x0)y=1;elsey=0;,p4：modifyto：y=0;if(x=0)if(x0)y=1;elsey=-1;,Return,#includemain()intx,y;print