C程序設(shè)計(jì)基礎(chǔ) 英文版 課件 Chapter 3 Program control structure

Chapter3ProgramControlStructure格式化的輸入輸出FANGWANGOutline3.1Statement3.2InputandOutput3.3TheSequenceStructure3.4TheSelectionStructure3.5TheloopStructure23.2.1SingleCharacterInput/OutputReadingandWritingCharactersUsinggetcharandputcharForsingle-characterinputandoutput,getchar

andputcharareanalternativetoscanfandprintf.writesacharacter:

putchar(a);readsonecharacter:

c=getchar();Likescanf,getchardoesn’tskipwhite-spacecharactersasitreads.#include<stdio.h>31.TheprintfFunctionPrintingtheValueofaVariable輸出變量的值Theprintffunctionmustbesuppliedwithaformatstring,followedbyanyvaluesthataretobeinsertedintothestringduringprinting:printf(“格式說(shuō)明符”,表達(dá)式1,表達(dá)式2,…);

printf(“formatstring”,expr1,expr2,…);

3.2.2FormattedInputandOutputTellsprintf()howtodisplaytheseargumentsArgumentsthatyouwanttodisplayprintf(“Iam%dyearsold\n",age);printf(“%d\n",age);Theformatstringmaycontainbothordinarycharacters

（普通字符）

andconversionspecifications(格式說(shuō)明符:beginwith%

)用格式說(shuō)明符先給要輸出的值占個(gè)位置。輸出時(shí)它會(huì)被要輸出的值替代

Aconversionspecificationisaplaceholderrepresentingavaluetobefilledinduringprinting.%d

isaplaceholderindicatingwherethevalueofi

istobefilledin.inti=3,j=5;printf(“Tomhas%dcats\n",i);printf(“Tomhas%dcatsandIhave%dcats!\n",i,j);Ordinarycharactersareprintedastheyappearinthestring;conversionspecificationsarereplaced.普通字符原樣輸出，格式說(shuō)明符會(huì)被要輸出的值（比如i）替代53.1TheprintfFunction%d–integers按整數(shù)形式輸出%f–floats 按小數(shù)形式輸出%d

worksonlyforint

variables;toprintafloat/double

variable,use%f

instead.Bydefault,

%f

displaysanumberwithsixdigitsafterthedecimalpoint.(%f默認(rèn)輸出6位小數(shù))6PrintingtheValueofaVariable7Example:inti;doublex；i=10; x=43.2892;

printf("i=%d,x=%f\n",i,x);Output:i=10,x=43.289200Classexercise4:outputCreateanewprojectnamed“ex04”declareavariabletostore3andanothervariabletostore1.3.display2variablesandseparatethemwithaspace.Thefilenamedoesn’tmatter,butdon’tusespace.89printf

candisplaythevalueofanynumericexpression.volume=height*length*width;

Thestatementsprintf("%d\n",volume);couldbereplacedbyprintf("%d\n",height*length*width);printf("%d\n",833+5);printf("%f\n",8.33);PrintingExpressions(輸出表達(dá)式的值)ReadingandWritingIntegers八、十六、無(wú)符號(hào)數(shù)輸入輸出格式符Readingandwritingunsigned,short,andlongintegersrequiresnewconversionspecifiers.Whenreadingorwritinganunsignedinteger,usetheletteru,o,x

insteadofdintheconversionspecification.

%u%o%x

unsignedintu;

scanf("%u",&u);/*readsuinbase10*/ printf("%u",u);/*writesuinbase10*/ scanf("%o",&u);/*readsuinbase8*/ printf("%o",u);/*writesuinbase8*/ scanf("%x",&u);/*readsuinbase16*/ printf("%x",u);/*writesuinbase16*/10ReadingandWritingIntegers十、八、十六、無(wú)符號(hào)數(shù)輸入輸出格式符Whenreadingorwritingashortinteger,puttheletterhinfrontofd,o,u,orx:%hd%ho%hu%hx

shorts;

scanf("%hd",&s); printf("%hd",s);Whenreadingorwritingalonginteger,puttheletterl

infrontofd,o,u,orx.%ld%lo%lu%lxWhenreadingorwritingalong

long

integer(C99only),putthelettersllinfrontofd,o,u,orx.113.1TheprintfFunctionTheminimumfieldwidth,m,specifiestheminimumnumberofcharacterstoprint.Ifthevaluetobeprintedrequiresfewerthanmcharacters,itisright-justifiedwithinthefield.%4ddisplaysthenumber123as?123.(?representsthespacecharacter.)Puttingaminussigninfrontofmcausesleftjustification.Thespecification%-4dwoulddisplay123as123?.Ifthevaluetobeprintedrequiresmorethanmcharacters,thefieldwidthautomaticallyexpandstothenecessarysize.m是最小輸出寬度，不足m列則左補(bǔ)空格，前面有負(fù)號(hào)則右補(bǔ)空格。如果數(shù)據(jù)本身大于m列，則全部輸出。例%4d,%10f12%04d%d—displayanintegerindecimalform.mindicatestheminimumnumberofdigitstodisplay(extrazerosareaddedtothebeginningofthenumberifnecessary).(例如%04d表示至少輸出4個(gè)數(shù)字，不夠4個(gè)就在前面補(bǔ)0)inti=123;printf("%04d\n",i);output0123133.1TheprintfFunctionConversionSpecificationsAconversionspecificationcanhavetheform%m.pXor%-m.pX,wheremandpareintegerconstantsandXisaletter.E.g:%10.2f,mis10,pis2,andXisf.Bothmandpareoptional;Inthespecification%10f,mis10andp(alongwiththeperiod)ismissing,butinthespecification%.2f,pis2andmismissing.143.1TheprintfFunctionConversionSpecificationsThemeaningoftheprecision,

p,dependsonthechoiceofX,theconversionspecifier.Toforce%f

todisplaypdigitsafterthedecimalpoint,put.p

between

%

andf.（%.2f表示整數(shù)部分原樣輸出，小數(shù)部分則輸出前兩位，%f默認(rèn)輸出整數(shù)和6位小數(shù)

）

doubleProfit=2150.4812;

printf("Profit:%.2f\n",profit); OutputProfit:2150.48 printf("Profit:%f\n",profit); OutputProfit:2150.48120015Classexercise5:inputandoutputCreateanewprojectnamed“ex05”DeclareavariabletostorePI(πtheratioofacircle'scircumferencetoitsdiameter:3.1415926535)andthendisplayitwith3digitsafterthedecimalpoint.Thefilenamedoesn’tmatter,butdon’tusespace.16%m.pf（m.p最小寬度.精度）%10.2fdoubleProfit=2150.4812;printf("Profit:%10.2f\n",profit);Output

Profit:2150.48

173.1TheprintfFunctionConversionspecifiersforfloating-pointnumbers: %e

—Exponentialformat.pindicateshowmanydigitsshouldappearafterthedecimalpoint(thedefaultis6).Ifpis0,nodecimalpointisdisplayed.(按指數(shù)形式輸出) %g

—Eitherexponentialformatorfixeddecimalformat,dependingonthenumber’ssize.pindicatesthemaximumnumberofsignificantdigitstobedisplayed.Thegconversionwon’tshowtrailingzeros.Ifthenumberhasnodigitsafterthedecimalpoint,gdoesn’tdisplaythedecimalpoint.183.1TheprintfFunctionEscapeSequences轉(zhuǎn)義字符The\ncodethatusedinformatstringsiscalledanescapesequence.Escapesequencesenablestringstocontainnonprinting(control)charactersandcharactersthathaveaspecialmeaning(suchas").Apartiallistofescapesequences:Alert(bell) \acausesanaudiblebeeponmostmachine響鈴Backspace \bmovesthecursorbackoneposition退格Newline \nadvancesthecursortothebeginningofthenextlineHorizontaltab\tmovesthecursortothenexttabstop1920\t：A

horizontaltabisalways8spaces(positions).Itisusedtocreatethetabspaces.3.1TheprintfFunctionEscapeSequencesAnothercommonescapesequenceis\",whichrepresentsthe"character: printf("\"Hello!\""); /*prints"Hello!"*/Toprintasingle\character,puttwo\charactersinthestring:

printf("\\"); /*printsone\character*/213.2ThescanfFunction輸入函數(shù)scanf

istheClibrary’scounterparttoprintf.scanfrequiresaformatstringtospecifytheappearanceoftheinputdata.Exampleofusingscanftoreadanintvalue: scanf("%d",&a);/*readsaninteger;storesintoa*/The&

symbolisusually(butnotalways)requiredwhenusingscanf.Readingafloatvaluerequiresaslightlydifferentcallofscanf: scanf("%f",&x);"%f"tellsscanftolookforaninputvalueinfloatformat(thenumbermaycontainadecimalpoint,butdoesn’thaveto).doublez;scanf("%lf",&z);22Classexercise6:inputCreateanewprojectnamed“ex06”Declareavariable“age”andenteryouragethendisplayit.233.2ThescanfFunction輸入函數(shù)scanfreadsinputaccordingtoaparticularformat.Ascanfformatstringmaycontainbothordinarycharactersandconversionspecifications.Inmanycases,ascanfformatstringwillcontainonlyconversionspecifications: inti,j; doublex,y;

scanf("%d%d%lf%lf",&i,&j,&x,&y);24Formatstringtellsscanf()howtheinputisformattedspecifytheappearanceoftheinputdataArgumentsareaddressofvariablesthatwillstorethevalueread3.2ThescanfFunction inti,j; doublex,y;

scanf("%d%d%lf%lf",&i,&j,&x,&y);Sampleinput: 1-20.3-4.0e3 scanfwillassign1,–20,0.3,and–4000.0toi,j,x,andy,respectively.253.2ThescanfFunctionHowscanfWorksAsitsearchesforanumber,scanfignoreswhite-spacecharacters(space,tab,andnew-line用空格，制表符，換行分隔).Acallofscanfthatreadsfournumbers: scanf("%d%d%lf%lf",&i,&j,&x,&y);Thenumberscanbeononelineorspreadoverseverallines:

1 -20.3 -4.0e3scanfseesastreamofcharacters(¤representsnew-line): ??1¤-20???.3¤???-4.0e3¤ ssrsrrrsssrrssssrrrrrr(s=skipped;r=read)scanf“peeks”atthefinalnew-linewithoutreadingit.263.2ThescanfFunctiontheprogrammermustcheckthatthenumberofconversionspecificationsmatchesthenumberofinputvariablesandthateachconversionisappropriateforthecorrespondingvariable.Anothertrapinvolvesthe&symbol,whichnormallyprecedeseachvariableinascanfcall.The&isusually(butnotalways)required,andit’stheprogrammer’sresponsibilitytoremembertouseit.27Classexercise7:inputCreateanewprojectnamed“ex07”declare4variables:Math,English,Computerasdoubletype;Enteryourmarkofthemandoutputthesumandtheaverage.28Classexercise8:inputCreateanewprojectnamed“ex08”declare4variables:volume,height,length,width;Computethevolumeofthisboxanddisplayit.29Howtowriteaprogram?Step1:declarevariablesStep2:inputdataStep3:calculateStep4:outputwhichdatatypetodeclaredependsonthesizeofthevalueforavariableyouneed.GetroomsStoredataCalculatePrinttheresult2.ThescanfFunctionOrdinaryCharactersinFormatStringsInputmustmatchtheformatstringExamples:Iftheformatstringis"%d/%d"andtheinputis3/5,scanf

succeeds.Iftheinputis35,scanffails,becausethe/intheformatstringdoesn’tmatchthespaceintheinput.

scanf("%d,%d",&i,&j);input:3,531NOJquestion2DateClassexercise9:#include<stdio.h>#include<stdlib.h>intmain(){intmonth,day,year;scanf("%d/%d/%d",&month,&day,&year);printf("%04d%02d%02d\n",year,month,day);return0;}Step1:declarevariablesStep2:inputdataStep3:output3.2ThescanfFunctionConfusingprintfwithscanfPuttinganew-linecharacterattheendofascanfformatstringisusuallyabadidea.Toscanf,anew-linecharacterinaformatstringisequivalenttoaspace;bothcausescanftoadvancetothenextnon-white-spacecharacter.Iftheformatstringis"%d\n",scanfwillskipwhitespace,readaninteger,thenskiptothenextnon-white-spacecharacter.Aformatstringlikethiscancauseaninteractiveprogramto“hang.”343.3TheSequenceStructureThesequencestructureTheselectionstructureTheloopstructure35Program

Control

Structures3typesoflogicstructuresinprogramming:SequencestructureSelectionstructureLoopstructureCControlLoopStatement1Statement2Statement3StatementnStatement1Statement23.4SelectionStatements選擇結(jié)構(gòu)

Aconditionalflowstatementisamechanismthatallowsyoutobranchyourprogramflowinoneormoredirectionsbasedontheresultofacertaintestif(a>b){printf(“a”);}else{printf(“b”);}選擇機(jī)構(gòu)首先測(cè)試?yán)ㄌ?hào)中的條件，根據(jù)條件成立與否來(lái)選擇對(duì)應(yīng)的語(yǔ)句執(zhí)行。41Statement1Statement2Classexercise9:whoiselderCreateanewprojectnamed“ex09”declare2variables:mom,dad;Inputtheirages;Comparetheiragesandprintwhoiselder.423.4.1RelationalExpressionsSeveralofC’sstatementsmusttestthevalueofanexpressiontoseeifitis“true”or“false.”Forexample,anifstatementmightneedtotesttheexpressiona>b;atruevaluewouldindicatethataisgreaterthanb.InC,acomparisonsuchasa>byieldsaninteger:either0(false)or1(true).關(guān)系（邏輯）表達(dá)式如果成立，則認(rèn)為該表達(dá)式的值為1（真），不成立則認(rèn)為表達(dá)式的值為0（假）。比如5>3,這個(gè)表達(dá)式的值為143C’srelationaloperators（關(guān)系運(yùn)算符） < lessthan > greaterthan <= lessthanorequalto >= greaterthanorequaltoTheseoperatorsproduce0(false)or1(true)whenusedinexpressions.

inta=1,b=2; printf(“%d\n”,a>b); output:0

floata=3.14,b=9.8; printf(“%d\n”,a<b); output:144LogicalExpressionsRelationalOperatorsTheprecedenceoftherelationaloperatorsislowerthanthatofthearithmeticoperators.Forexample,a+b

<

c

+

dmeans(a

+

b)

<

(c

+

d).Therelationaloperatorsareleftassociative.關(guān)系運(yùn)算符優(yōu)先級(jí)比算術(shù)運(yùn)算符低45LogicalExpressions == equalto != notequaltoTheequalityoperatorsareleftassociativeandproduceeither0(false)or1(true)astheirresult.Theequalityoperatorshavelowerprecedencethantherelationaloperators,sotheexpression

a<b==a<b isequivalentto

(a<b)==(a<b)46RelationalOperatorsTheexpression a<b<cislegal,butdoesnottestwhetherjliesbetweeniandk.Sincethe<operatorisleftassociative,thisexpressionisequivalentto (a<b)<cThe1or0producedbyi

<

jisthencomparedtok.Thecorrectexpressionisi

<

j

&&

j

<

k.Howabout5>3>2473.4.1LogicalExpressionsLogicalOperatorsMorecomplicatedlogicalexpressionscanbebuiltfromsimpleronesbyusingthelogicaloperators:

! logicalnegation非 && logicaland與 || logicalor或The!operatorisunary,while&&and||arebinary.Thelogicaloperatorsproduce0or1astheirresult.48LogicalOperatorsThe!operatorhasthesameprecedenceastheunaryplusandminusoperators.Theprecedenceof&&and||islowerthanthatoftherelationalandequalityoperators.Forexample,a

<

b

&&

x==

ymeans(a

<

b)

&&

(x

==

y).The!operatorisrightassociative;&&and||areleftassociative.49Classexercise10:question7leapyear①Anyyearthatisevenlydivisibleby4butnotevenlydivisibleby100isaleapyeary%4==0&&y%100!=0Or②Anyyearthatisevenlydivisibleby400isaleapyeary%400==0inty;scanf("%d",&y);if(y%400==0||(y%4==0&&y%100!=0))printf("Yes\n");elseprintf("No\n");

LogicalOperators!expr

hasthevalue1ifexprhasthevalue0.expr1&&expr2

hasthevalue1ifthevaluesofexpr1

andexpr2arebothnonzero.expr1||expr2

hasthevalue1ifeitherexpr1orexpr2(orboth)hasanonzerovalue.Inallothercases,theseoperatorsproducethevalue0.Thelogicaloperatorstreatanynonzerooperandasatruevalueandanyzerooperandasafalsevalue.0為假，非0為真53LogicalOperatorsBoth&&and||perform“short-circuit”evaluation:theyfirstevaluatetheleftoperand,thentherightone.Ifthevalueoftheexpressioncanbededucedfromtheleftoperandalone,therightoperandisn’tevaluated.Example: (i!=0)&&(j>0) (i!=

0)isevaluatedfirst.Ifiisn’tequalto0,then(j

>

0)isevaluated.Ifiis0,theentireexpressionmustbefalse,sothere’snoneedtoevaluate(j

>

0).&&and||如果左邊的表達(dá)式就可以確定整個(gè)表達(dá)式的值，右邊表達(dá)式不會(huì)被執(zhí)行。54LogicalExpressionsLogicalOperatorstheshort-circuitnatureofthe&&and||

Example:

i>0&&++j>0

Ifi

>

0isfalse,then++j

>

0isnotevaluated,sojisn’tincremented.example： v1=v2=2; n1=1;n2=2;n3=3;n4=4;t=(v1=n1>n2)&&(v2=n3>n4) v1=?v2=?553.4.3TheifStatementTheifstatementallowsaprogramtochoosebetweentwoalternativesbytestinganexpression.Initssimplestform,theifstatementhastheform

if(expression)

statementWhenanifstatementisexecuted,expressionisevaluated;ifitsvalueisnonzero

(orture),statementisexecuted.Example: if(line_num==MAX_LINES) line_num=0;5657E.g1：inputaninterger，ifitispositivethendisplayit

intmain(){intx;scanf(”%d”,&x);if(x>0)printf(”%d\n”,x);return0;}Classexercise11:PositivenumberTheifStatementConfusing==(equality)with=(assignment)isperhapsthemostcommonCprogrammingerror.Thestatement

if(i==0)… testswhetheriisequalto0.Thestatement if(i=0)… assigns0toi,thentestswhethertheresultisnonzero.58TheifStatementOftentheexpressioninanifstatementwilltestwhetheravariablefallswithinarangeofvalues.Totestwhether0￡

i<n:

if(0<=i&&i<n)…Totesttheoppositecondition(iisoutsidetherange):

if(i<0||i>=n)…59TheifStatementCompoundStatementsIntheifstatementtemplate,noticethatstatementissingular,notplural:

if(expression)statementTomakeanifstatementcontroltwoormorestatements,useacompoundstatement.Acompoundstatementhastheform

if(expression)

{statements}Puttingbracesaroundagroupofstatementsforcesthecompilertotreatitasasinglestatement.60TheifStatement61CompoundStatementsExample: if(expression) {line_num=0;page_num++;}Acompoundstatementisusuallyputonmultiplelines,withonestatementperline: if(expression){ line_num=0; page_num++; }Eachinnerstatementstillendswithasemicolon,butthecompoundstatementitselfdoesnot.TheifStatementCompoundStatementsExampleofacompoundstatementusedinsideanifstatement: if(line_num==MAX_LINES){ line_num=0; page_num++;

}62E.g2：inputthevaluesofaandb,comparethem,ifaislessthanb,thenswaptheirvalues.63

intmain(){doublea,b,t;scanf(”%lf%lf”,&a,&b);if(a<b){t=a;a=b;b=t;}//Swaptheirvaluesprintf(”%fisgreaterthan%f\n”,a,b);return0;}TheifStatementTheelseClauseAnifstatementmayhaveanelseclause: if(expression)statement

elsestatementThestatementthatfollowsthewordelseisexecutediftheexpressionhasthevalue0.Example:if(a>b)max=a; elsemax=b;64TheifStatementTheelseClauseWhenanifstatementcontainsanelseclause,whereshouldtheelsebeplaced?ManyCprogrammersalignitwiththeifatthebeginningofthestatement.Innerstatementsareusuallyindented,butifthey’reshorttheycanbeputonthesamelineastheifandelse: if(a>b)max=a; elsemax=b;656666

#include<stdio.h>#include<math.h>intmain(){doublex,y;scanf(”%lf”,&x);if(x>=0)y=x;elsey=x*x*x-1.0;printf(”y=%f\n”,y); return0;}xx≥0x3-1x<0Classexercise12:piecewisefunction--enterxandcomputeyy=Declarevariablesx,yInputxCalculateyDisplayy#include<math.h>pow(a,b);67Classexercise13:Heron‘sformulaTocalculatetheareaofatriangleusingHeron'sformula,youneedtoknowthelengthsofallthreesidesofthetriangle.Inputthelengthof3sides,calculatetrianglearea.Ifyoucan’tmakeatrianglewiththem,display“ERROR”.Declarevariablea,b,cInput3sidesDetermineif3sidelengthscanmakeatriangleIfyes,calculatetheareaandoutputitIfnot,display“ERROR”.Hint:sqrt(2)#include<math.h>Trap:1/2is0Todetermineif3sidelengthscanformatriangle,usethetriangleinequalitytheorem,whichstatesthatthesumof2sidesofatrianglemustbegreaterthanthethirdside.Therefore,allyouhavetodoisaddtogethereachcombinationof2sidestoseeifit'sgreaterthanthethirdside.68#include<stdio.h>#include<math.h>intmain(){doublea,b,c,s,area;scanf(”%lf%lf%lf”,&a,&b,&c);if(a+b>c&&a+c>b&&b+c>a)

{

s=(a+b+c)/2.0;area=sqrt(s*(s-a)*(s-b)*(s-c));printf(”area=%8.3f\n”,area);}elseprintf(”ERROR\n”);}TheifStatement69It’snotunusualforifstatementstobenestedinsideotherifstatements:

if(i>j)

if(i>k) max=i; else max=k;

else

if(j>k) max=j; else max=k;Aligningeachelsewiththematchingifmakesthenestingeasiertosee.If語(yǔ)句嵌套形式TheifStatementTheelseClauseToavoidconfusion,pleaseaddbraces:

if(i>j)

{ if(i>k) max=i; else max=k;

}

else

{ if(j>k) max=j; else max=k;

}70TheifStatement71TheelseClauseSomeprogrammersuseasmanybracesaspossibleinsideifstatements: if(i>j){ if(i>k){max=i;}

else{max=k;} }else{ if(j>k){max=j;}

else{max=k; } }TheifStatementThe“Danglingelse”ProblemWhenifstatementsarenested,the“danglingelse”problemmayoccur: if(y!=0) if(x!=0) result=x/y; else printf("Error:yisequalto0\n");Theindentationsuggeststhattheelseclausebelongstotheouterifstatement.However,Cfollowstherulethatanelseclausebelongstothenearestifstatementthathasn’talreadybeenpairedwithanelse.72TheifStatementThe“Danglingelse”ProblemTomaketheelseclausepartoftheouterifstatement,wecanenclosetheinnerifstatementinbraces: if(y!=0){ if(x!=0) result=x/y; }else printf("Error:yisequalto0\n");Usingbracesintheoriginalifstatementwouldhaveavoidedtheprobleminthefirstplace.73Classexercise13-2:question7FindthebiggestnumberTheifStatementTheelseClauseAdvantagesofusingbracesevenwhenthey’renotrequired:Makesprogramseasiertomodify,becausemorestatementscaneasilybeaddedtoanyiforelseclause.Helpsavoiderrorsthatcanresultfromforgettingtousebraceswhenaddingstatementstoaniforelseclause.75TheifStatementCascadedifStatementsA“cascaded”ifstatementisoftenthebestwaytotestaseriesofconditions,stoppingassoonasoneofthemistrue.級(jí)聯(lián)式CascadedifStatements

if(expression1)

statement1

elseif(expression2)

statement2 …

elseif(expression3)

statement3

else

statement476TheifStatementCascadedifStatementsExample:

if(n>0) printf(“nispostive\n");

elseif(n==0) printf("nis0\n");

else printf("nisnegative\n");77Classexercise14:lowercase&uppercaseDeclareavariableofchartype.·Readacharacterusinggetchar().·Ifitislowercase,thenconvertittouppercase:a--A.·Ifitisuppercase,thenconvertittolowercase:A--a.·Displaythischaracterusingputchar().78Classexercise15:GradeInputyourgrade,ifit’s4,display“Excellent”……..(cascadedif

)grade:4 Excellent 3 Good 2 Average 1 Poor 0 Failing other Illegalgrade79Acascadedifstatementcanbeusedtocompareanexpressionagainstaseriesofvalues: if(grade==4) printf("Excellent"); elseif(grade==3) printf("Good"); elseif(grade==2) printf("Average"); elseif(grade==1) printf("Poor"); elseif(grade==0) printf("Failing"); else printf("Illegalgrade");

Question15-2:Howmanydigitsscanf("%d",&a);if(0<a&&a<=9) printf("1\n"); elseif(a<=99)printf("2\n");elseif(a<=999)printf("3\n",a);8282#include’’stdio.h”intmain(){intg;printf(”Enterscore:”);scanf(”%d”,&g);if(g<0||g>100)printf(”INPUTERROR!”);elseif(g>=80)printf(”A”);elseif(g>=70)printf(”B”);elseif(g>=60)printf(”C”);elseprintf(”D”);return0;}80～100分A檔70～79分B檔60～69分C檔0～59分D檔TheswitchStatementAcascadedifstatementcanbeusedtocompareanexpressionagainstaseriesofvalues: if(grade==4) printf("Excellent"); elseif(grade==3) printf("Good"); elseif(grade==2) printf("Average"); elseif(grade==1) printf("Poor"); elseif(grade==0) printf("Failing"); else printf("Illegalgrade");

83TheswitchStatementTheswitchstatementisanalternative: switch(grade){ case4:printf("Excellent"); case3:printf("Good"); case2:printf("Average"); case1:printf("Poor"); case0:printf("Failing"); default:printf("Illegalgrade"); //Whenvalueofexpressiondoesn'tmatchwithanycase }84 switch(grade){ case4:printf("Excellent");

break; case3:printf("Good");

break; case2:printf("Average");

break; case1:printf("Poor");

break; case0:printf("Failing");

break; default:printf("Illegalgrade");

break; }Classexercise16:dayDeclareintvariable–dayInputday(1,2,3….)Outputwhat

day

of

the

weekitis85switch

(day)

{

case

1:

printf(“1:MONDAY\n”);

break;

case

2:

printf("2:TUESDAY\n”);break;

case

3:

printf(“3:WEDNESDAY\n”);

break;

case

4:

printf("4:THURSDAY\n”);

break;

case

5:

printf("5:FRIDAY\n”);

break;

case

6:

printf("6:SATURDAY\n”);

break;

case

7:printf("7:SUNDAY\n”);break;

default:

printf("other:INVALIDINPUT\n”);break;

}1:

MONDAY

2:

TUESDAY3:

WEDNESDAY4:

THURSDAY;

5:

FRIDAY6:

SATURDAY7:

SUNDAYother: INVALIDINPUTTheswitchStatementAswitchstatementmaybeeasiertoreadthanacascadedifstatement.switchstatementsareoftenfasterthanifstatements.Mostcommonformoftheswitchstatement: switch(expression){ caseconstant-expression:statements … case