C++面向对象程序设计双语教程（第3版）课件 class 4-classes objects-1

ObjectivesTounderstanddataabstractionfurtherTobeabletoknowwhataclassisandhowtocreateanobjectTo

understandencapsulationandinformationhiding01IntroductiontoStructures03Classesand

Objects02DataAbstraction04AccessControl05EncapsulationandInformationHiding01IntroductiontoStructureIntroductiontoStructuresCase

Study

1Problem:Writeaprogramforagradebookofagivencourse.Agradebookincludescourse’sname,student’sIDandgrade;Inputallinformationoncourseandstudent;Calculatetheaveragegradeofthecourse;Printthegradebook.Requirements:DatastructureA

datastructure

isagroupofdataelementsgroupedtogetherunderonename.structgradeBook{stringcourseName;stringstudentID;intstudentGrade;};Datatypes:built-intypes,e.g.int,char,floatandsoon.IntroductiontoStructuresinCstruct

gradeBook{stringcourseName;stringstudentID[studentNum];intstudentGrade[studentNum];};voidinput(gradeBook&oop);doubleaverage(gradeBook&oop);voidprint(gradeBook&oop);intmain(){gradeBookgbOOP;input(gbOOP);print(gbOOP);return0;}adatatype,auser-definedtypeMembersAstructuretypeisanaggregationofdifferentdatatypesunderonename.Dotoperator(.)Arrowoperator(->)Memberaccessoperatorsvoidinput(gradeBook&oop){cin>>

oop.courseName;for(inti=0;i<studentNum;i++)cin>>

oop.studentID[i]>>

oop.studentGrade[i];}IntroductiontoStructuresinC++struct

gradeBook{stringcourseName;stringstudentID[studentNum];intstudentGrade[studentNum];voidinput(){cin>>courseName;for(inti=0;i<studentNum;i++)cin>>studentID[i]>>studentGrade[i];}doubleaverage(){intsum=0;for(inti=0;i<studentNum;i++)sum+=studentGrade[i];return(double)sum/studentNum;}voidprint(){cout<<

"coursename:"

<<courseName<<endl;for(inti=0;i<studentNum;i++)cout<<studentID[i]<<

"|"

<<studentGrade[i]<<endl;cout<<

"course'saverage:"

<<average()<<endl;}};intmain(){gradeBookgbOOP;gbOOP.input();gbOOP.print();return0;}MemberfunctionsData

membersMembersStructurewithmemberfunctionsIntroductiontoStructureinC++struct

gradeBook{stringcourseName;stringstudentID[studentNum];intstudentGrade[studentNum]={0};voidinput();doubleaverage();voidprint();};intmain(){gradeBookgbOOP;gbOOP.input();gbOOP.print();return0;}void

gradeBook::input(){cin>>courseName;for(inti=0;i<studentNum;i++)cin>>studentID[i]>>studentGrade[i];}double

gradeBook::average(){intsum=0;for(inti=0;i<studentNum;i++)sum+=studentGrade[i];return(double)sum/studentNum;}C++11:InitializerinthestructureDefiningaStructureinCCase

Study

2Problem:WriteaprogramofaDatetype.Adateincludesyear,month,day;Inputallinformationonadate;Printthedate.Requirements:struct

Date{intyear,month,day;};intmain(){Datetoday,d[2];//arraycin>>today.year>>today.month>>today.day;cout<<today.year<<endl;cin>>d[0].year>>d[0].month>>d[0].day;cin>>d[1].year>>d[1].month>>d[1].day;cout<<d[1].year<<d[1].month<<d[1].day<<endl;Date*dptr=&today;//pointerdptr->year=2010;cout<<dptr->year<<dptr->month<<dptr->day<<endl;Date&rd=today;//referencecout<<rd.year<<rd.month<<rd.day<<endl;return0;}Dotoperator(.)Arrowoperator(->)MemberaccessoperatorsDefiningaStructureinCstruct

Date{ intyear,month,day;};voidinput_date(Date&date,int

y,int

m,int

d){date.year=y;date.month=m;date.day=d;}voidprint_date(Date&date){cout<<date.year<<date.month<<date.day<<endl;}intmain(){Datetoday;input_date(today,2017,10,1);print_date(today);return0;}DefiningaStructureinC++struct

Date{intyear,month,day;voidinput_date(inty,intm,intd);voidprint_date();};void

Date::input_date(int

y,int

m,int

d){year=y;month=m;day=d;}void

Date::print_date(){cout<<year<<month<<day<<endl;}intmain(){Datetoday;today.input_date(2016,10,12);today.print_date();return0;}Memberfunctions02DataAbstractionDataAbstractionLogicalpropertiesofthegradeBook,Datestructuredtypes:Threemembervariables,e.g.courseName,studentID,studentGrade,year,month,dayDeclarationoffunctions,e.g.input,average,print,input_date,print_date,…Implementation:DefinitionoffunctionsDataabstractionisdefinedasaprocessofseparatingthelogicalpropertiesofdatafromitsimplementationdetail.Dateabstractionisusedasamethodinanobject-orientedprogramming.AbstractDataTypesDefinitionofaDateADTdataTypeNamegradeBook,DateDomaineachdatatyperepresentsvalues,e.g.courseName,studentID,studentGrade,year,month,dayOperationsInputtheinformationofcourseandstudentsPrintagradebookinputadateprintadateAbstractdatatype(ADT)Adatatypeseparatesthelogicalpropertiesfromtheimplementationdetail.03ClassesandObjectsClassesandObjectsprint_dateinput_dateyear,month,daydateClasses

areanexpandedconceptof

datastructures:likedatastructures,theycancontaindatamembers,buttheycanalsocontainfunctionsasmembers.Classisauser-definedtypeinaprogramminglanguagethatisusedtorepresentanabstractdatatype(ADT).Aclassisasetorcollectionofabstractedobjectsthatsharecommoncharacteristics.printinputcourseName,studentIDstudentGradegradeBookDefinitionofaClassclassDate{

private:

intday;

intmonth;

intyear;

public:

voidinput_date(intd,intm,inty);

voidprint_date();};datamembermemberfunctionsaccesscontrolspecifierClassnameclassclass_name

{accesscontrolspecifier:datamembers;memberfunctions;};Syntaxtodeclareaclasstype

Thecomponentsofaclassarecalledthemembersoftheclass.Themembersoftheclassmaybeeitherdatatypeorfunctions.Dataintheclassarecalleddatamembers.Functionsdeclaredwithintheclassdefinitionarecalledmemberfunctions.DefinitionofaClassconst

intstudentNum=3;class

gradeBook{public:voidinput();doubleaverage();voidprint();private:stringcourseName="";stringstudentID[studentNum]={""};intstudentGrade[studentNum]={0};};memberfunctionsdatamemberClassnameaccesscontrolspecifierDefininganObjectDatemy_birthday;objectDeclarelocalobjectse.g.inanyfunctionDeclareglobalobjectsDeclareobjectsasclassmembersDeclareanobjectarraye.g.Dateday[10];Declareconstantobjectse.g.constDatedayDeclareobjectreferencesorpointerse.g.Date*pDay;Declarestaticobjecte.g.staticDatedayWhenaclassisused,anobjectisdeclared.Date*today;Dated1[3];ConceptofanobjectAnobject

isavariableofaclasstype,orclassinstance.Whenisanobjectdeclared?Inwhichwayisanobjectdeclared?Anobjectisdeclaredinthesameasbuilt-inttypesintmain(){Datetoday;today.input_date(2016,10,12);today.print_date();return0;}HowtoAccessMemberFunctionsinaClassMemberfunctionswithinaclasscanbeinvokedbyaclassvariable(i.e.object).objectaccessingmemberfunctionclassDate{

private:

intday;

intmonth;

intyear;

public:

voidinput_date(intd,intm,inty);

voidprint_date();};DefinitionofMemberFunctionsclass

Date{private:intday,month,year;public:voidinput_date(int

d,int

m,int

y){ day=d;month=m;year=y;}voidadd_year(int

n){year+=n;}voidadd_month(int

n){month+=n;}voidadd_day(int

n){day+=n;}};class

Date{private:intday,month,year;public:voidinput_date(int

d,int

m,int

y);voidadd_year(int

n);voidadd_month(int

n);voidadd_day(int

n);};inline

void

Date::add_year(n){year+=n;}inlinevoidadd_month(int

n){month+=n;}inlinevoidadd_day(int

n){day+=n;}DefinememberfunctionswithinaclassTheinlinefunctionsinstructcompilertoinsertcompletebodyofthefunctionwhereverthatfunctiongotusedincode.intmain(){Dateday;day.input_date(9,8,2020);day.add_year(1);return0;}DefinitionofMemberFunctionsBecausedifferentclassescanhavememberfunctionswiththesamename,wemustspecifytheclassnamewhendefiningamemberfunction.DefinememberfunctionsoutsidetheClassclass

Date{private:intday,month,year;public:voidinput_date(int

d,int

m,int

y);voidadd_year(int

n);voidadd_month(int

n);voidadd_day(int

n);};void

Date::input_date(int

d,int

m,int

y){day=d;month=m;year=y;}void

Date::add_year(n){year+=n;}void

Date::add_month(int

n){month+=n;}voidadd_day(int

n)//error{day+=n;}DefinitionofMemberFunctionsDefinememberfunctionsoutsidetheClassconst

intstudentNum=3;class

gradeBook{public:voidinput();doubleaverage();voidprint();private:stringcourseName="";stringstudentID[studentNum]={""};intstudentGrade[studentNum]={0};};void

gradeBook::input(){cin>>courseName;for(inti=0;i<studentNum;i++)cin>>studentID[i]>>studentGrade[i];}double

gradeBook::average(){intsum=0;for(inti=0;i<studentNum;i++)sum+=studentGrade[i];return(double)sum/studentNum;}void

gradeBook::print(){cout<<

"coursename:"

<<courseName<<endl;for(inti=0;i<studentNum;i++){ cout<<setw(9)<<right<<studentID[i]

<<setw(7)<<right<<studentGrade[i]<<endl;}cout<<

"----------------------------\n";cout<<

"Theaveragegrade:"

<<average()<<endl;}04AccessControlAccessControlclass

Date{private:intday,month,year;public:voidinput_date(int

d,int

m,int

y);voidadd_year(int

n);voidadd_month(int

n);voidadd_day(int

n);};accessspecifierAccesscontrol

isenforcedatcompiletime,notatrun-time.Whenamemberisaccessed,thecompilercheckstheaccessspecifierforit.Anaccessspecifierisoneofthreekeywords:private,publicorprotectedclass

Date{intday,month,year;public:voidinput_date(int

d,int

m,int

y);voidadd_year(int

n);voidadd_month(int

n);voidadd_day(int

n);};class

Date{public:voidinput_date(int

d,int

m,int

y);voidadd_year(int

n);voidadd_month(int

n);voidadd_day(int

n);private:intday,month,year;};class

Date{public:voidinput_date(int

d,int

m,int

y);private:voidadd_year(int

n);voidadd_month(int

n);voidadd_day(int

n);private:intday,month,year;};AccessControlTheprivatepartofthememberswithinaclasscanbeusedonlybymemberfunctionsofthisclass.(default)Thepublicpartofthememberswithaclasscanbeusedbymemberfunctionsofthisclassorotherfunctionsoutsidetheclass.intmain(){Datetoday;today.input_date(12,9,2021);return0;}accessspecifier-privateaccessspecifier-publicclass

Date{public:voidinput_date(int

d,int

m,int

y);voidadd_year(int

n);voidadd_month(int

n);voidadd_day(int

n);private:intday,month,year;};voidDate::input_date(int

d,int

m,int

y){day=d;month=m;year=y;}intmain(){Datetoday;today.day=15;//errorreturn0;}05EncapsulationandInform