C语言基础教程课件(English)ch03

AFirstBookofANSIC

FourthEditionChapter3ProcessingandInteractiveInputAFirstBookofANSIC,FourthEdition2ObjectivesAssignmentMathematicalLibraryFunctionsInteractiveInputFormattedOutputAFirstBookofANSIC,FourthEdition3Objectives(continued)SymbolicConstantsCaseStudy:InteractiveInputCommonProgrammingandCompilerErrorsAFirstBookofANSIC,FourthEdition4AssignmentThegeneralsyntaxforanassignmentstatementis variable=operand;Theoperandtotherightoftheassignmentoperator(=)canbeaconstant,avariable,oranexpressionTheequalsigninCdoesnothavethesamemeaningasanequalsigninalgebralength=25;isread“lengthisassignedthevalue25”Subsequentassignmentstatementscanbeusedtochangethevalueassignedtoavariablelength=3.7;length=6.28;AFirstBookofANSIC,FourthEdition5Assignment(continued)TheoperandtotherightoftheequalsigninanassignmentstatementcanbeavariableoranyvalidCexpression sum=3+7; product=.05*14.6;Thevalueoftheexpressiontotherightof=iscomputedfirstandthenthecalculatedvalueisstoredinthevariabletotheleftof=Variablesusedintheexpressiontotherightofthe=mustbeinitializediftheresultistomakesenseamount+1892=1000+10*5isinvalid!AFirstBookofANSIC,FourthEdition6Assignment(continued)Ifwidthwasnotinitialized,thecomputerusesthevaluethathappenstooccupythatmemoryspacepreviously(compilerwouldprobablyissueawarning)AFirstBookofANSIC,FourthEdition7Assignment(continued)=hasthelowestprecedenceofallthebinaryandunaryarithmeticoperatorsintroducedinSection2.4Multipleassignmentsarepossibleinthesamestatement a=b=c=25;All=operatorshavethesameprecedenceOperatorhasright-to-leftassociativityc=25;b=c;a=b;AFirstBookofANSIC,FourthEdition8ImplicitTypeConversionsDatatypeconversionstakeplaceacrossassignmentoperatorsdoubleresult;result=4;//integer4isconvertedto4.0Theautomaticconversionacrossanassignmentoperatoriscalledanimplicittypeconversionintanswer;answer=2.764;//2.764isconvertedto2Heretheimplicitconversionisfromahigherprecisiontoalowerprecisiondatatype;thecompilerwillissueawarningAFirstBookofANSIC,FourthEdition9ExplicitTypeConversions(Casts)Theoperatorusedtoforcetheconversionofavaluetoanothertypeisthecastoperator (dataType)expressionwheredataType

isthedesireddatatypeoftheexpressionfollowingthecastExample:Ifsumisdeclaredasdoublesum;,(int)sumistheintegervaluedeterminedbytruncatingsum’sfractionalpartAFirstBookofANSIC,FourthEdition10AssignmentVariationssum=sum+10isnotanequation—itisanexpressionthatisevaluatedintwomajorstepsAFirstBookofANSIC,FourthEdition11AssignmentVariations(continued)AFirstBookofANSIC,FourthEdition12AssignmentVariations(continued)AFirstBookofANSIC,FourthEdition13AssignmentVariations(continued)Assignmentexpressionslikesum=sum+25canbewrittenusingthefollowingoperators:+=-=*=/=%=sum=sum+10canbewrittenassum+=10price*=rateisequivalenttoprice=price*rateprice*=rate+1isequivalenttoprice=price*(rate+1)AFirstBookofANSIC,FourthEdition14AccumulatingThefirststatementinitializessumto0ThisremovesanypreviouslystoredvalueinsumthatwouldinvalidatethefinaltotalApreviouslystorednumber,ifithasnotbeeninitializedtoaspecificandknownvalue,isfrequentlycalledagarbagevalueAFirstBookofANSIC,FourthEdition15Accumulating(continued)AFirstBookofANSIC,FourthEdition16Accumulating(continued)AFirstBookofANSIC,FourthEdition17CountingAcountingstatementisverysimilartotheaccumulatingstatement variable=variable+fixedNumber;Examples:i=i+1;andm=m+2;Incrementoperator(++):variable=variable+1canbereplacedbyvariable++or++variableAFirstBookofANSIC,FourthEdition18Counting(continued)AFirstBookofANSIC,FourthEdition19Counting(continued)AFirstBookofANSIC,FourthEdition20Counting(continued)Whenthe++operatorappearsbeforeavariable,itiscalledaprefixincrementoperator;whenitappearsafteravariable,itiscalledpostfixincrementoperatork=++n;isequivalentton=n+1;//incrementnfirstk=n;//assignn'svaluetokk=n++;isequivalenttok=n;//assignn'svaluetokn=n+1;//andthenincrementnAFirstBookofANSIC,FourthEdition21Counting(continued)Prefixdecrementoperator:theexpressionk=--nfirstdecrementsthevalueofnby1beforeassigningthevalueofntokPostfixdecrementoperator:theexpressionk=n--firstassignsthecurrentvalueofntonandthenreducesthevalueofnby1AFirstBookofANSIC,FourthEdition22Counting(continued)AFirstBookofANSIC,FourthEdition23MathematicalLibraryFunctionsAFirstBookofANSIC,FourthEdition24MathematicalLibraryFunctions(continued)Theargumenttosqrtmustbefloating-pointvalue;passinganintegervalueresultsinacompilererrorReturnvalueisdouble-precisionMustinclude#include<math.h>AFirstBookofANSIC,FourthEdition25MathematicalLibraryFunctions(continued)AFirstBookofANSIC,FourthEdition26MathematicalLibraryFunctions(continued)AFirstBookofANSIC,FourthEdition27MathematicalLibraryFunctions(continued)ArgumentneednotbeasingleconstantAFirstBookofANSIC,FourthEdition28MathematicalLibraryFunctions(continued)Thestep-by-stepevaluationoftheexpression 3.0*sqrt(5*33-13.91)/5 is(seenextslide)AFirstBookofANSIC,FourthEdition29MathematicalLibraryFunctions(continued)AFirstBookofANSIC,FourthEdition30MathematicalLibraryFunctions(continued)Determinethetimeittakesaballtohitthegroundafterithasbeendroppedfroman800-foottowertime=sqrt(2*distance/g),whereg=32.2ft/sec2AFirstBookofANSIC,FourthEdition31MathematicalLibraryFunctions(continued)AFirstBookofANSIC,FourthEdition32InteractiveInputAFirstBookofANSIC,FourthEdition33InteractiveInput(continued)Thisprogrammustberewrittentomultiplydifferentnumbersscanf()isusedtoenterdataintoaprogramwhileitisexecuting;thevalueisstoredinavariableItrequiresacontrolstringasthefirstargumentinsidethefunctionnameparenthesesAFirstBookofANSIC,FourthEdition34InteractiveInput(continued)Thecontrolstringpassedtoscanf()typicallyconsistsofconversioncontrolsequencesonlyscanf()requiresthatalistofvariableaddressesfollowthecontrolstringscanf("%d",&num1);AFirstBookofANSIC,FourthEdition35InteractiveInput(continued)AFirstBookofANSIC,FourthEdition36InteractiveInput(continued)ThisstatementproducesapromptAddressoperator(&)AFirstBookofANSIC,FourthEdition37InteractiveInput(continued)scanf()canbeusedtoentermanyvaluesscanf("%f%f",&num1,&num2);//"%f%f"isthesameAspacecanaffectwhatthevaluebeingenterediswhenscanf()isexpectingacharacterdatatypescanf("%c%c%c",&ch1,&ch2,&ch3);storesthenextthreecharacterstypedinthevariablesch1,ch2,andch3;ifyoutypexyz,thenxisstoredinch1,ablankisstoredinch2,andyisstoredinch3scanf("%c%c%c",&ch1,&ch2,&ch3);causesscanf()tolookforthreecharacters,eachcharacterseparatedbyexactlyonespaceAFirstBookofANSIC,FourthEdition38InteractiveInput(continued)Inprintingadouble-precisionnumberusingprintf(),theconversioncontrolsequenceforasingle-precisionvariable,%f,canbeusedWhenusingscanf(),ifadouble-precisionnumberistobeentered,youmustusethe%lfconversioncontrolsequencescanf()doesnottestthedatatypeofthevaluesbeingenteredInscanf("%d%f",&num1,&num2),ifuserenters22.87,22isstoredinnum1and.87innum2AFirstBookofANSIC,FourthEdition39Caution:ThePhantomNewlineCharacterAFirstBookofANSIC,FourthEdition40Caution:ThePhantomNewlineCharacter(continued)ThefollowingisasamplerunforProgram3.10:Typeinacharacter:mThekeystrokejustacceptedis109Typeinanothercharacter:Thekeystrokejustacceptedis10AFirstBookofANSIC,FourthEdition41Caution:ThePhantomNewlineCharacter(continued)AFirstBookofANSIC,FourthEdition42Caution:ThePhantomNewlineCharacter(continued)AFirstBookofANSIC,FourthEdition43AFirstLookatUser-InputValidationAFirstBookofANSIC,FourthEdition44AFirstLookatUser-InputValidation(continued)Aswritten,Program3.12isnotrobustTheproblembecomesevidentwhenauserentersanon-integervalueEnterthreeintegernumbers:1020.6820Theaverageof10,20,and-858993460is-286331143.333333Handlinginvaliddatainputiscalleduser-inputvalidationValidatingtheentereddataeitherduringorimmediatelyafterthedatahavebeenenteredProvidingtheuserwithawayofreenteringanyinvaliddataAFirstBookofANSIC,FourthEdition45FormattedOutput618124---148OutputisnotalignedAFirstBookofANSIC,FourthEdition46FormattedOutput(continued)618124---148FieldwidthspecifierAFirstBookofANSIC,FourthEdition47FormattedOutput(continued)AFirstBookofANSIC,FourthEdition48FormatModifiersLeftjustification:printf("%-10d",59);producesthedisplay59٨٨٨٨٨٨٨٨Explicitsigndisplay:printf("%+10d",59);producesthedisplay٨٨٨٨٨٨٨+59Formatmodifiersmaybecombined%-+10dwouldcauseanintegernumbertobothdisplayitssignandbeleft-justifiedinafieldwidthof10spacesTheorderoftheformatmodifiersisnotcritical%+-10disthesameAFirstBookofANSIC,FourthEdition49OtherNumberBases[Optional]Thedecimal(base10)valueof15is15.Theoctal(base8)valueof15is17.Thehexadecimal(base16)valueof15isf.AFirstBookofANSIC,FourthEdition50OtherNumberBases(continued)AFirstBookofANSIC,FourthEdition51OtherNumberBases(continued)Thedecimalvalueoftheletterais97.Theoctalvalueoftheletterais141.Thehexvalueoftheletterais61.AFirstBookofANSIC,FourthEdition52OtherNumberBases(continued)AFirstBookofANSIC,FourthEdition53SymbolicConstantsLiteraldatareferstoanydatawithinaprogramthatexplicitlyidentifiesitselfLiteralvaluesthatappearmanytimesinthesameprogramarecalledmagicnumbersCallowsyoutodefinethevalueoncebyequatingthenumbertoasymbolicname#defineSALESTAX0.05#definePI3.1416AlsocalledsymbolicconstantsandnamedconstantsAFirstBookofANSIC,FourthEdition54SymbolicConstants(continued)#signisasignaltoaCpreprocessorAFirstBookofANSIC,FourthEdition55CaseStudy:InteractiveInputAFirstBookofANSIC,FourthEdition56CaseStudy:InteractiveInput(continued)AFirstBookofANSIC,FourthEdition57CommonProgrammingErrorsForgettingtoassigninitialvaluestoallvariablesbeforethevariablesareusedinanexpressionCallingsqrt()withanintegerargumentForgettingtousetheaddressoperator,&,infrontofvariablenamesinascanf()functioncallNotincludingthecorrectcontrolsequencesinscanf()functioncallsforthedatavaluesthatmustbeenteredIncludingamessagewithinthecontrolstringpassedtoscanf()AFirstBookofANSIC,FourthEdition58CommonProgrammingErrors(continued)Terminatinga#definecommandtothepreprocessorwithasemicolonPlacinganequalsignina#definecommandwhenequatingasymbolicconstanttoavalueUsingtheincrementanddecrementoperatorswithvariablesthatappearmorethanonceinthesameexpressionBeingunwillingtotestaprogramindepthAFirstBookofANSIC,FourthEdition59CommonCompilerErrorsAFirstBookofANSIC,FourthEdition60CommonCompilerErrors(continued)AFirstBookofANSIC,FourthEdition61Summary