C++大學(xué)教程課后習(xí)題答案4

Chapter5

FunctionsforAllSubtasks

1.SolutionstoSelectedProgrammingProjects

Detailedsolutionsselectedprojectsarepresentedhere.Therestareessentiallythesame

problems,exceptforwhatisbeingconverted.Notesabouttheremainingproblemsare

included.

Oneofthemoreimportantthingsinprogrammingisplanning,evenforthesimplest

program.Iftheplanningisthorough,thecodingwillbeeasy,andtheonlyerrorslikelyto

beencounteredaresyntaxerrors,usuallycausedbyeithertypingerrors,aboundary

conditionproblem(frequently,anoffbyoneerror),or(wehopenot)lackofknowledgeof

thelanguagedetails.

1ConvertTime

Task：Convert24hourtimenotationto12hourAM/PMnotation.

Generalcomments:Thestudentshouldnotethat:

a)Theconvertfunctionhasboundarycasesthatrequirecarefulattention.

b)ALLofthiscommentaryandplanningshouldbedonePRIORtobeginningtowritethe

program.Oncethisisdonetheprogramisalmostwritten.Thesoonercodingbegins,the

longertheprogramwilltaketodocorrectly.

c)Whentestingforequality,asin

if(12==hours)

puttheconstantfirst.Thecompilerwillcatcherrorssuchasif(12=hours)whicharehard

toseeotherwise.Imademanyerrorsofthistypewhilecodingthisproblem.

1

Copyright?2008PearsonEducation,Inc.PublishingasPearsonAddison-Wesley

//file：ch5progl.cc

//Task：Convert24hourtimenotationto12hourAM/PM

//notation.

//Input:24hourtime

//Output：corresponding12hourtime,withAM/PMindication

//Required：3functions：input,conversion,andoutput.

//keepAM/PMinformationinacharvariable

//allowrepeatatuser*soption

//Notes：conversionfunctionwillhaveacharreference

//parametertoreturnwhetherthetimeisAM/PM.Other

//parametersarerequired.

#include<iostream>

usingnamespacestd；

voidinput(int&hours24zint&minutes)；

//Precondition：input(hours,minutes)iscalledwith

//argumentscapableofbeingassigned.

//Postcondition：

//userispromptedfortimein24hourformat：

//HH：MMZwhere0<=HH<24z0<=MM<60.

//hoursissettoHH,minutesissettoMM.

//KNOWNBUG:NOCHECKINGISDONEONINPUTFORMAT.Omitting

//the''："(colon)fromtheinputformat''eats,zonecharacter

//fromtheminutesdata,andsilentlygiveserroneous

//results.

voidconvert(int&hourszchar&M)；

//Precondition：0<=hours<24,

//Postcondition：

//ifhours>12,//Note：definitelyintheafternoon

//hoursisreplacedbyhours-12,

//AMPMissetto1P,

//elseif12==hours//boundaryafternoonhour

//AMPMissetto1PL//hoursisnotchanged.

//elseif0==hours//boundarymorninghour

//hours=hours+12；

//AMPM='A1；

//else

//(hours<12)

//AMPMissetto1A,；

//hoursisunchanged

voidoutput(inthourszintminuteszcharAMPM)；

//Precondition：

//0<hours<=12z0<=minutes<60,

//AMPM=='P?orAMPM=='A'

//Postconditions：

//timeiswrittenintheformat

//HH:MMAMorHH:MMPM

intmain()

(

inthours,minutes；

charAMPM,ans；

do

(

input(hourszminutes)；

convert(hourszAMPM)；

output(hours,minuteszAMPM)；

cout<<"EnterYorytocontinue,

<<nanythingelsequits.n

<<endl；

cin>>ans；

}while(1Y,==ans||1y'==ans)；

return0；

)

voidinput(int&hours24,int&minutes)

(

charcolon；

cout<<"Enter24hourtimeintheformatHH：MM"

<<endl；

cin>>hours24>>colon>>minutes；

)

//Precondition：0<=hours<24,

//Postcondition：

//ifhours>=12z

//hoursisreplacedbyhours-12,

//AMPMissetto1P1

//else//(hours<12)

//hoursisunchangedandAMPMissetto'A1

voidconvert(int&hourszchar&M)

(

if(hours>12)//definitelyintheafternoon

(

hours=hours-12；

AMPM='P1;

)

elseif(12==hours)//boundaryafternoonhour

AMPM=1P1；//buthoursisnotchanged,

elseif(0==hours)//boundarymorninghour

hours=hours+12；

AMPM,A1;

else//(hours<12)//definitelymorninghour

AMPM='A1;//hoursisunchanged

voidoutput(inthours,intminutes,charAMPM)

cout<<"Timein12hourformat：<<endl

<<hours<<"："<<minutes<<

<<AMPM<<*M1<<endl;

Atypicalrunfollows：

20:33:03:-/AW$a.out

Enter24hourtimeintheformatHH：MM

0:30

Timein12hourformat：

12:30AM

EnterYorytocontinue,anythingelsequits.

y

Enter24hourtimeintheformatHH：MM

2：15

Timein12hourformat：

2：15AM

EnterYorytocontinue,anythingelsequits.

y

Enter24hourtimeintheformatHH：MM

Enter24hourtimeintheformatHH：MM

11:30

Timein12hourformat：

11:30AM

EnterYorytocontinue,anythingelsequits.

y

Enter24hourtimeintheformatHH：MM

12:30

Timein12hourformat：

12:30PM

EnterYorytocontinue,anythingelsequits.

y

Enter24hourtimeintheformatHH：MM

23:59

Timein12hourformat：

11:59PM

EnterYorytocontinue,anythingelsequits.

n

20:33:59:~/AW$

2.Time

//Waitingtime

//Problem2fSavitch,ProgrammingandProblemSolvingwithC++5th

//

//filech5.2.cpp

//Programinput:currenttimeandawaitingtime

//eachtimeisnumberofhoursandanumberofminutes.

//Programoutputisisthetimethewaitingperiodcompletes.

//Use24hourtime.Allowuserrepeat.

//Notes:The24hourboundary,i.e.,whenthetimewrapstothe

//nextdayisimportanthere.

//

//KnownBugs:Ifthecompletiontimewouldbeinadaylater

//thanthenextdayafterthestart,thisprogramgivesincorrect

//results.

//

#include<iostream>

voidinput(int&hours24,int&minutes)

usingstd::cout;

usingstd::cin;

usingstd::endl;

charcolon;

cout<<"Enter24hourtimeintheformatHH:MM

<<endl;

cin>>hours24>>colon>>minutes;

)

voidoutput(inthours,intminutes)

{

usingstd::cout;

usingstd::cin;

usingstd::endl;

cout<<"Timein24hourformat:\nn

<<hours<<"："<<minutes<<endl;

)

intmain()

{

usingstd::cout;

usingstd::cin;

usingstd::endl;

inttim一Hours,timeMinutes,waitHours,waitMinutes,

finishHours,finishMinutes;

cout<<'*Computecompletiontimefromcurrenttimeandwaiting

period\nM;

charans=*y1;

while(1y'==ans||'Y1==ans)

{

cout<<"Currenttime:\nn;

input(timeHours,timeMinutes);

cout<<"Waitingtime:\nn;

input(waitHours,waitMinutes);

finishHours=timeHours+waitHours;

finishMinutes=timeMinutes+waitMinutes;

finishHours+=finishMinutes/60;

if(finishHours>=24)

(

finishHours%=24;

cout<<"Completiontimeisinthedayfollowingthestart

time\n',;

}

finishMinutes%=60;

cout<<"Completionn;

output(finishHours,finishMinutes);

cout<<n\n\nEnterYorytocontinue,anyotherhalts\n\nH;

cin>>ans;

)

return0;

)

/*

Typicalrun

Computecompletiontimefromcurrenttimeandwaitingperiod

Currenttime:

Enter24hourtimeintheformatHH:MM

12:30

Waitingtime:

Enter24hourtimeintheformatHH:MM

15:40

Completiontimeisinthedayfollowingthestarttime

CompletionTimein24hourformat:

4:10

EnterYorytocontinue.anyotherhalts

y

Currenttime:

Enter24hourtimeintheformatHH:MM

8:30

Waitingtime:

Enter24hourtimeintheformatHH:MM

15:10

CompletionTimein24hourformat:

23:40

EnterYorytocontinue,anyotherhalts

n

Pressanykeytocontinue

*/

3.Project3Modifyproject2touse12hourtime.

Weprovidesuggestionsonhowtoproceedinsolvingthisproblem.

Thisproblemisdifferentfrom#2onlyinthedetailsofmanaging12hourtime.Thewait

timeintervalcouldbeanynumberofhoursandminutes,sotheoutputshouldprovidethe

numberofdaysthatelapsefromthestarttimeuntilcompletion.

Youmaywantaninputroutinethatverifiesthatyouhaveentered

legitimate12hourtimedata,i.e.hoursbetwee1and12,minutesbetween0

and59,andincludeseitheranAforAMoraPforPM.

Writecodetoconvertthe12hourstarttimeto24hourtimeandusethecodefrom#3to

computerthefinishtime.

Decideonhowtohandlefinishtimesthatfallinsomelaterday,thenconvert24hourtime

to12hourtimeandoutputthatusingcodefrom#2.

4.Statistics

Computeaverageandstandarddeviationof4entries.

GeneralremarksareinthecodefilewhichIpresenthere:

//filech5prob4.cc

ftinclude<iostream>

usingnamespacestd；

/*

Task：Writeafunctionthatcomputesaverage(Iwillcall

thisthearithmeticmeanorsimplythemean)andstandard

deviationoffourscores.Theaverageormean,avg,is

computedas

avg=(si+s2+s3+s4)/4

Thestandarddeviationiscomputedas

stddeviation

4

wherea=avg.Notethatsomestatisticiansmaywishtouse3

insteadof4.Wewilluse4.

Input：scoressis2s3s4

Output：standarddeviationandmean.

Required：Thefunctionistohave6parameters.Thisfunction

callstwoothersthatcomputethemeanandthestddeviation.

Adriverwithaloopshouldbewrittentotestthefunction

attheuser'soption.

*/

//functiondeclaration(orprototype)

//Whenused,themathlibrarymustbelinkedtothe

//executable.

#include<cmath>//forsqrt

usingnamespacestd；

voidaverage(doublesi,doubles2,doubles3,

doubles4,doubledavg)

(

avg=(si+s2+s3+s4)/4；

//Preconditions：averagefunctionmusthavebeencalledon

//thedata,andthevalueoftheaveragepassedintothe

//parametera

//Postconditions：Standarddeviationispassedbackin

//thevariablestdDev

voidsD(doublesizdoubles2,doubles3,doubles4,

doubleazdoubledstdDev)

stdDev=sqrt((si-a)*(si-a)+(s2-a)*(s2-a)

+(s3-a)*(s3-a)+(s4-a)*(s4-a))/4；

)

voidstatistics(doublesi,doubles2zdoubles3zdoubles4,

doubledavg；doubledstdDev)；

//Preconditions：thisfunctioniscalledwithanysetof

//values.Verylargeorverysmallnumbersaresubjectto

//errorsinthecalculation.Analysisofthissortoferror

//isbeyondthescopeofthischapter.

//Postconditions：avgissettothemeanofsizs2,s3zs4

//andstdDevissettothestandarddeviationofsi..s4

//functiondefinition：

voidstatistics(doublesi,doubles2,doubles3,doubles4,

doubledavg,doubledstdDev)

{

average(si,s2,s3,s4,avg)；

sD(si,s2,s3,s4,avg,stdDev)；

)

intmain()

(

doublesi,s2,s3,s4,avg,stdDev；

charans；

do

(

cout<<"Enter4decimalnumbers,"

<<nIwillgiveyouthemean"

<<endl

<<"andstandarddeviationofthedataH<<endl；

cin>>si>>s2>>s3>>s4；

statistics(sizs2,s3,s4,avgzstdDev)；

cout<<"meanof"<<si<<*'n<<s2<<"n<<s3

<<""<<s4<<nis"<<avg<<endl

<<*'thestandarddeviationofH

<<"thesenumbersisn<<stdDev<<endl；

n

cout<<yorYcontinueszanyotherterminates"<<endl；

cin>>ans；

}while(1Y*==ans||1y1==ans)；

return0；

)

Atypicalrunfollows：

21:44:35:-/AW$a.out

Enter4decimalnumbers,Iwillgiveyouthemean

andstandarddeviationofthedata

12.313.410.59.0

meanof12.313.410.59is11.3

thestandarddeviationofthesenumbersis0.841873

yorYcontinues,anyotherterminates

y

Enter4decimalnumbers,Iwillgiveyouthemean

andstandarddeviationofthedata

1234

meanof1234is2.5

thestandarddeviationofthesenumbersis0.559017

yorYcontinues,anyotherterminates

n

21:45:05:-/AW$

5.Changemakerproblem.

Onlynotesonthesolutionareprovidedforthisproblem.Inmydiscussionofthisproblem,

Iincludeawordortwoonalgorithmdevelopment,concluding(sometimesonlythe

following).

Agreedyalgorithmworksforthisproblem.Agreedyalgorithmmakeslocallyoptimal

choicesateachpointinthesequenceofpointsinthesolution,inthehopethatthelocally

optimalchoiceswillresultinagloballyoptimalsolution.Thisworkssurprisinglyoften,

includingthisproblem.Itisinterestingtomethatthegreedyalgorithmfailsforsome

nationalcoinage.

Isuggestthatthestudentwritecodetochoosethelargestnumberofcoinsofthelargest

denominationfromthelistofcoinnotyetused.Repeatthisontheremainingamountof

moneyfordecreasingdenominationsuntilnomorecoinsareleft.

6.Conversion1

Conversionoffeet/inchestometers:

//File:Ch4Prob6.cc

//Task：Convertfeet/inchestometers

//Input：alengthinfeetandincheszwithpossibledecimal

//partofinches

//Output：alengthinmeters,with2decimalplaceszwhich

//arethe1centimeters*specifiedintheproblem.

//Required：functionsforinput,computation,andoutput.

//Includealooptorepeatthecalculationattheuser1s

//option.Remarks：Thecomputationisasimpleconversionfrom

//feet+inchestofeetwithadecimalpart,thentometers.

//Outputisrestrictedto2decimalplaces.

//

//By1metersandcentimeters1theauthormeansthatthe

//outputistobemeterswithtwodecimalplaces-whichis

//metersandcentimeters.Imentionthisbecausemystudents

//alwaysstumbleatthisbecauseofalackofknowledgeof

//themetricsystem.

#include<iostream>

usingnamespacestd；

voidinput(int&feet,doubledinches)；

//Precondition：functioniscalled

//Postcondition：

//PromptgiventotheuserforinputintheformatFF工工，

//whereFFisintegernumberoffeetandIIisadouble

//numberofinches.feetandinchesarereturnedasentered

//bytheuser.

voidconvert(intfeet,doubleinches,doubledmeters)；

//Preconditions：

//REQUIREDCONSTANTS:INCHES_PER_FOOTzMETERS_PER_FOOT

//inches<12,feetwithinrangeofvaluesforinttype

//Postconditions：

//metersassigned0.3048*(feet+inches/12)

//observethatthecentimeterrequirementismetby

//thevalueofthefirsttwodecimalplacesoftheconverted

//feetzinchesinput.

voidoutput(intfeetzdoubleincheszdoublemeters)；

//input：theformalargumentformetersfitsintoadouble

//output：

//"thevalueoffeet；inches'1<feet；inches>

//nconvertedtometers,centimetersisn<meters>

//wheremetersisdisplayedasanumberwithtwodecimal

//places

intmain()

intfeet；

doubleincheszmeters；

charans；

do

(

input(feetzinches)；

convert(feetzincheszmeters)；

output(feet,inches,meters)；

cout<<"Yorycontinueszanyothercharacterquits

<<endl；

cin>>ans；

}while(1Y,==ans||1y1==ans)；

return0；

)

voidinput(int&feetzdoubledinches)

(

cout<<"Enterfeetasaninteger："<<flush；

cin>>feet；

cout<<"Enterinchesasadouble："<<flush；

cin>>inches；

)

constdoubleMETERS_PER_FOOT=0.3048;

constdoubleINCHES_PER_FOOT=12.0;

voidconvert(intfeetzdoubleinches,doubledmeters)

meters=METERS_PER_FOOT*(feet+

inches/INCHES_PER_FOOT);

)—一

voidoutput(intfeet,doubleinches,doublemeters)

(

//incheszmetersdisplayedasanumberwithtwodecimal

//places

cout.setf(ios：：showpoint)；

cout.setf(ios：：fixed)；

cout.precision(2)；

cout<<nthevalueoffeet,inches"<<feet<<","

<<inches<<endl

<<”convertedtometers,centimetersis"

<<meters<<endl；

)

/*

Atypicalrunfollows：

06:59:16:-/AW$a.out

Enterfeetasaninteger：5

Enterinchesasadouble：7

thevalueoffeetzinches5,7.00

convertedtometerszcentimetersis1.70

Yorycontinueszanyothercharacterquits

y

Enterfeetasaninteger：245

Enterinchesasadouble：0

thevalueoffeet,inches245,0.00

convertedtometers,centimetersis74.68

Yorycontinues,anyothercharacterquits

q

06:59:49:?/AW$

*/

7.Conversion2

Conversionofmetersbacktocentimeters.

//file：ch5prob7.cc

//Task：Convertmeterswithcentimeters(justthedecimal

//partofmeters)tofeet/inches

//

//Input：alengthinfeetandincheszwithpossibledecimal

//partofinches

//Output：Alengthmeasuredinfeetwithanydecimalfraction

//convertedtoinchesbymultiplyingby12.Fractionsofan

//incharerepresentedby2decimalplaces.

//

//Required：functionsforinput,computation,andoutput.

//Includealooptorepeatthecalculationattheuser's

//option.

//

//Remark：Thecomputationisasimpleconversionfrommeters

//tofeetzinches,whereincheshasadecimalpart.

//Outputisrestrictedto2decimalplaces

//Comment：PleaseseeProblem4fordiscussionof1metersand

//centimeters'

#include<iostream>

usingnamespacestd；

voidinput(double&meters)；

//Precondition：functioniscalled

//Postcondition：

//Promptgiventotheuserforinputofanumberofmetersas

//adouble.inputofadoubleformetershasbeenaccepted

voidconvert(int&feet,doubledinches,doublemeters)；

//Preconditions：

//REQUIREDCONSTANTS:INCHES_PER_FOOTzMETERS_PER_FOOT

//Postconditions：

//feetisassignedtheintegerpartofmeters(after

//conversiontofeetunits)inchesisassignedthe

//fractionalpartoffeet(afterconversiontoinchunits

voidoutput(intfeet,doubleincheszdoublemeters)；

//input：theformalargumentformetersfitsintoadouble

//output：

//"thevalueofmeterszcentimetersis："<meters>

//"convertedtoEnglishmeasureis"

HHH

//<feet>feetz<inches>inches”

//wheremetersisdisplayedasanumberwithtwodecimal

//places

intmain()

(

intfeet；

doubleinches,meters；

charans；

do

(

input(meters)；

convert(feet,incheszmeters)；

output(feet,incheszmeters)；

cout<<nYorycontinues,anyothercharacterquits

<<endl;

cin>>ans；

}while(1Y1==ans||1y*==ans)；

return0；

)

voidinput(doubledmeters)

(

cout<<"Enteranumberofmetersasadouble\nH；

cin>>meters；

}

constdoubleMETERS_PER_FOOT=0.3048;

constdoubleINCHES_PER_FOOT=12.0;

voidconvert(int&feet,doubledinches,doublemeters)

(

doubledfeet；

dfeet=meters/METERS_PER_FOOT；

feet=int(dfeet)；

inches=(dfeet-feet)*INCHES_PER_FOOT；

)——

voidoutput(intfeet,doubleincheszdoublemeters)

(

//metersisdisplayedasadoublewithtwodecimalplaces

//feetisdisplayedasintzinchesasdoublewithtwo

//decimalplaces

cout.setf(ios：：showpoint)；

cout.setf(ios：：fixed)；

cout.precision(2)；

cout<<"Thevalueofmeterszcentimeters”<<endl

<<meters<<*'meters"<<endl

<<"convertedtoEnglishmeasureisn<<endl

<<feet<<”feet,H<<inches<<?'inches"

<<endl；

)

/*

Atypicalrunfollows：

07:56:28:-/AW$a.out

Enteranumberofmetersasadouble

6.0

Thevalueofmeterszcentimeters

6.00meters

convertedtoEnglishmeasureis

19feetz8.22inches

Yorycontinues,anyothercharacterquits

y

Enteranumberofmetersasadouble

75

Thevalueofmeterszcentimeters

75.00meters

convertedtoEnglishmeasureis

246feetz0.76inches

Yorycontinues,anyothercharacterquits

q

07:56:40:~/AW$

*/

8.Conversion3

Thisexercisecombinesthetwopreviousexercises.Convertbetweenfeet/inchesand

meters.Thedirectionistheuser'soption.

//file：ch5prob8.cc

//Task：Convertbetweenmetersandfeet/inchesatuser*s

//optionWithinconversion,allowrepeatedcalculation

//afterendofeitherconversion,allowchoiceofanother

//conversion.

//Input：Atprogramrequest,userselectsdirectionof

//conversion.Inputiseitherfeet/inches(withdecimal

//fractionforinches)ORmeterswith2placedecimal

//fractionthatrepresentsthecentimeters.

//Output：Dependsonuserselection：eithermetersor

//feetandinches.

//Method：Suggestedbyproblemstatement：useif-else

//selectionbasedontheuserinputtochoosebetween

//functionswrittenforproblems4and5above.

//Required：functionsforinputzcomputation,andoutput.

//Includealooptorepeatthecalculationattheuser*s

//option.

#include<iostream>

usingnamespacestd；

voidinputM(doubledmeters)；

//Precondition：functioniscalled

//Postcondition：

//Promptgiventotheuserforinputofanumberofmeters

//asadouble

voidinputE(int&feet,doubledinches)；

//Precondition：functioniscalled

//Postcondition：

//PromptgiventotheuserforinputintheformatFFII,

//whereFFisanintnumberoffeetandIIisadoublenumber

//ofinchesfeetandinchesarereturnedasenteredbythe

//user.

voidconvertEtoM(intfeet,doubleinches,

doubledmeters)；

//Preconditions：

//REQUIREDCONSTANTS:INCHES_PER_FOOTzMETERS_PER_FOOT

//inches<12,feetwithinrangeofvaluesforanint

//Postconditions：

//metersassigned0.3048*(feet+inches/12)

//Observethattherequirementtoproducecentimetersismet

//bythevalueofthefirsttwodecimalplacesofmeters.

voidconvertMtoE(int&feetzdoubledinches,

doublemeters)；

//Preconditions：

//REQUIREDCONSTANTS:INCHES_PER_FOOTzMETERS_PER_FOOT

//Postconditions：

//thevariablefeetisassignedtheintegerpartof

//meters/METERS_PER_FOOT

//thevariableinchesisassignedthefractionalpartof

//feetafterconversiontoinchunits.

voidoutput(intfeet,doubleinches,doublemeters)；

//input：theformalargumentformetersfitsintoadouble

//output：

//"thevalueoffeet,inches"<feetzinches>

nn

//correspondstometerszcentimetersis<meters>

//wheremetersisdisplayedasanumberwithtwodecimal

//places

voidEnglishToMetrie()；

//requestsEnglishmeasure,convertstometric,outputsboth

voidMetricToEnglish()；

//requestmetricmeasure,convertstoEnglish,outputsboth

intmain()

(

charans；

do

(

intwhich；

cout<<"Enter1forEnglishtoMetricorn<<endl

<<"Enter2forMetrictoEnglishconversion"

<<endl；

cin>>which；

if(1==which)

EnglishToMetric()；

else

MetricToEnglish()；

cout<<nYoryallo