国外C语言程序设计英文lectureppt课件.ppt

Computerprogramming,Lecture3,Lecture3:Outline,ProgramLoopingKochanchap.5TheforStatementRelationalOperatorsNestedforLoopsIncrementOperatorProgramInputforLoopVariantsThewhileStatementThedoStatementThebreakStatementThecontinueStatement,Executingaprogram,Program=listofstatementsEntrypoint:thepointwheretheexecutionstartsControlflow:theorderinwhichtheindividualstatementsareexecuted,Statement1Statement2Statement3Statement4Statement5Statement6Statement7Statement8,StructureofaCprogram,#includeintmain(void)intvalue1,value2,sum;value1=50;value2=25;sum=value1+value2;printf(Thesumof%iand%iis%in,value1,value2,sum);return0;,EntrypointofaCprogram,Sequentialflowofcontrol,Controllingtheprogramflow,Formsofcontrollingtheprogramflow:ExecutingasequenceofstatementsRepeatingasequenceofstatements(untilsomeconditionismet)(looping)Usingatesttodecidebetweenalternativesequences(branching),Statement1Statement2Statement3Statement4Statement5Statement6Statement7Statement8,ProgramLooping,Looping:doingonethingoverandoverProgramloop:asetofstatementsthatisexecutedrepetitivelyforanumberoftimesSimpleexample:displayingamessage100times:,printf(“hello!n”);printf(“hello!n”);printf(“hello!n”);printf(“hello!n”);printf(“hello!n”);,Repeat100timesprintf(“hello!n”);,Programlooping:enablesyoutodevelopconciseprogramscontainingrepetitiveprocessesthatcouldotherwiserequiremanylinesofcode!,Theneedforprogramlooping,#includeintmain(void)inttriangularNumber;triangularNumber=1+2+3+4+5+6+7+8;printf(Theeighthtriangularnumberis%in,triangularNumber);return0;,Whatifwehavetocomputethe200-th(1000-th,etc)triangularnumber?,Exampleproblem:computingtriangularnumbers.(Then-thtriangularnumberisthesumoftheintegersfrom1throughn),InC:3differentstatementsforlooping:for,while,do,Example200thtriangularnumber,n=1,triangularNumber=triangularNumber+n,n=200,n=n+1,yes,no,triangularNumber=0,PrinttriangularNumber,Statementbeforeloop,init_expression,loop_condition,statement,loop_expression,Statementafterloop,Example-for,/*Programtocalculatethe200thtriangularnumberIntroductionoftheforstatement*/#includeintmain(void)intn,triangularNumber;triangularNumber=0;for(n=1;n=200;n=n+1)triangularNumber=triangularNumber+n;printf(The200thtriangularnumberis%in,triangularNumber);return0;,Theforstatement,for(init_expression;loop_condition;loop_expression)programstatement,init_expression,Programstatement,loop_condition,Loopexpression,yes,no,1,2,3,4,5,Theforstatement,for(n=1;n=200;n=n+1)triangularNumber=triangularNumber+n;,1,2,3,4,5,yes,no,Howforworks,Theexecutionofaforstatementproceedsasfollows:1.Theinitialexpressionisevaluatedfirst.Thisexpressionusuallysetsavariablethatwillbeusedinsidetheloop,generallyreferredtoasanindexvariable,tosomeinitialvalue.2.Theloopingconditionisevaluated.Iftheconditionisnotsatisfied(theexpressionisfalsehasvalue0),theloopisimmediatelyterminated.Executioncontinueswiththeprogramstatementthatimmediatelyfollowstheloop.3.Theprogramstatementthatconstitutesthebodyoftheloopisexecuted.4.Theloopingexpressionisevaluated.Thisexpressionisgenerallyusedtochangethevalueoftheindexvariable5.Returntostep2.,Infiniteloops,Itsthetaskoftheprogrammertodesigncorrectlythealgorithmssothatloopsendatsomemoment!/Programtocount1+2+3+4+5#includeintmain(void)inti,n=5,sum=0;for(i=1;i=n;n=n+1)sum=sum+i;printf(“%i%i%in,i,sum,n);return0;,Whatiswronghere?Doestheloopend?,Relationaloperators,Therelationaloperatorshavelowerprecedencethanallarithmeticoperators:ab+cisevaluatedasa(b+c),ATTENTION!Donotconfuse:the“isequalto”operator=andthe“assignment”operator=,ATTENTIONwhencomparingfloating-pointvalues!Onlycomparisonsmakesense!,Exampleforwithabodyof2,/Programtogenerateatableoftriangularnumbers#includeintmain(void)intn,triangularNumber;printf(TABLEOFTRIANGULARNUMBERSnn);printf(nSumfrom1tonn);printf(-n);triangularNumber=0;for(n=1;ninalaterchapter!,Readsintegerfromkeyboard,Itspolitetodisplayamessagebefore,Nestedloops,#includeintmain(void)intn,number,triangularNumber,counter;for(counter=1;counter=5;+counter)printf(Whattriangularnumberdoyouwant?);scanf(%i,Rememberindentations!,forloopvariants,Multipleexpressions(commabetween)for(i=0,j=10;idoCriteria:Numberofrepetitions:Indefiniteloops-whileCountingloops-forInC,youcanactuallyrewriteanywhileasaforandviceversa!,Example:whilevsfor,#includeintmain(void)intcount=1;while(count=5)printf(%in,count);+count;return0;,#includeintmain(void)intcount;for(count=1;count=5;count+)printf(%in,count);return0;,ThebreakStatement,CanbeusedinordertoimmediatelyexitingfromaloopAfterabreak,followingstatementsintheloopbodyareskippedandexecutioncontinueswiththefirststatementaftertheloopIfabreakisexecutedfromwithinnestedloops,onlytheinnermostloopisterminated,Thebreakstatement,Programmingstyle:dontabusebreak!.while(number!=0)/Statementstodosomethinginloopprintf(Stop,answer1:);scanf(%i,/verybadideatodothis,Similartothebreakstatement,butitdoesnotmaketheloopterminate,justskipstothenextiteration,Thecontinuestatement,Thecontinuestatement,Continuealsonotsogoodstyle!.w