C++程序设计PPT

3,1,Chapter6.,Looping,3,2,Aloopisarepetitioncontrolstructure.itcausesasinglestatementorblocktobeexecutedrepeatedly,Whatisaloop?,3,3,TwoTypesofLoops,countcontrolledloopsrepeataspecifiednumberoftimesevent-controlledloopssomeconditionwithintheloopbodychangesandthiscausestherepeatingtostop,3,4,WhileStatement,SYNTAXwhile(Expression)./loopbody.NOTE:Loopbodycanbeasinglestatement,anullstatement,orablock.,3,5,Whentheexpressionistestedandfoundtobefalse,theloopisexitedandcontrolpassestothestatementwhichfollowstheloopbody.WHILELOOP,FALSE,TRUE,bodystatement,Expression,3,6,aninitializationoftheloopcontrolvariableanexpressiontotestforcontinuingtheloopanupdateoftheloopcontrolvariabletobeexecutedwitheachiterationofthebody,Count-controlledloopcontains,3,7,intcount;count=4;/initializeloopvariablewhile(count0)/testexpressioncoutcountendl;/repeatedactioncount-;/updateloopvariablecout“Done”0)coutcountendl;count-;cout“Done”0)coutcountendl;count-;cout“Done”0)TRUEcoutcountendl;count-;cout“Done”thisBP;total=total+thisBP;count+;/updatecout“Thetotal=“totalmonthday;/primingreadwhile(!(month=2,3,31,Examples,cin.get(inChar);while(inChar!=n)coutthisBP;coutdataValuesentinel;while(sentinel=1)/=cindataValuesentinel;/infiniteloop,3,34,End-of-FileControlledLoop,dependsonfactthatafilegoesintofailstatewhenyoutrytoreadadatavaluebeyondtheendofthefile,3,35,/End-of-filecontrolledlooptotal=0;myInfilethisBP;/primingreadwhile(myInfile)/whilelastreadsuccessfultotal=total+thisBP;myInfilethisBP;/readanothercoutthisBP;/readanothercoutthisBP;if(thisBP=200)isSafe=false;/changeflagvalueelsecountGoodReadings+;coutcountGoodReadingsnumber;sum=sum+number;/summingcount+;,3,42,PreviousandCurrentValues,writeaprogramthatcountsthenumberof!=operatorsinaprogramfilekeeptrackofcurrentandpreviouscharacters,3,43,intcount;charprevious;charcurrent;count=0;inFile.get(previous);/primingreadsinFile.get(current);while(inFile)if(current=)/readanother,/counting!=operatorinafile,3,44,initializeouterloopwhile(outerloopcondition).initializeinnerloopwhile(innerloopcondition)innerloopprocessingandupdate.,PatternofaNestedLoop,3,45,AnExample,inFile.get(inChar);while(inFile)/outerloopintcommaCount=0;while(inChar!=n)/innerloopif(inChar=,)commaCount+;inFile.get(inChar);coutcommaCountendl;inFile.get(inChar);,countingcommasonalineofafilewithmanylines.,3,46,AnotherExample,intx=0,count=0;while(x100)inty=0;while(y10)count+;y+;x+;coutcounthowMany;/primingread,3,51,while(myInfile)/lastreadsuccessfulpatientCount+;coutthisBP;count+;totalForPatient=totalForPatient+thisBP;average=totalForPatient/float(howMany);coutthisIDhowMany;/anotherread,3,52,cout“Therewere“patientCount“patientsonfile.”endl;coutkind;total=total+price;count+;cout“Totalis:“total0/Line1while(inFile)/Line2/Line3sum=sum+number;/Line4inFilenumber;/Line5/Line6A)betweenlines1and2B)betweenlines2and3C)betweenlines3and4D)betweenlines4and5E)Noprimingreadisnecessary.,3,77,CHOICE,A,3,78,CHOICE,Giventheinputdata25106-1whatistheoutputofthefollowingcodefragment?(Allvariablesareoftypeint.)sum=0;cinnumber;while(number!=-1)cinnumber;sum=sum+number;coutsumendl;A)15B)41C)40D)16E)nooutput-thisisaninfiniteloop,3,79,CHOICE,A,3,80,CHOICE,Afterexecutionofthefollowingcode,whatisthevalueoflength?(countandlengthareoftypeint.)length=5;count=4;while(count=100)length=length-2;elselength=count*length;count+;A)600B)100C)98D)20,3,81,CHOICE,C,3,82,CHOICE,Inthefollowingcodefragment,asemicolonappearsattheendofthelinecontainingtheWhile