C++面向对象程序设计双语教程（第3版）-参考答案 刘嘉敏 【ch07】Polymorphism and Virtual Functions

Chapter7PolymorphismandVirtualFunctions1.Writetheoutputofthefollowingprogram.略。2.Writetheoutputofthefollowingprogram.略。3.GiventhedefinitionofaPersonclassasfollows:DesignthetwoclassesStudentandTeacher.TheyarederivedfromclassPerson.(1)ClassStudenthasthepropertiesofname,id,classNoandstudyTimeperweek;ClassTeacherhasthepropertiesofname,id,departmentandworkTimeperweek.(2)Calculatethework/studenttime.Calculatingmethodsaredefinedasfollows:Thestudytimeofastudentistheclassquantitymultipliedby2(hour)perweek;Theworktimeofateacheristheteachingquantitymultiplied2(hour)perweek.(3)DisplaytheinformationforclassesStudentandTeacher.```cpp#include<iostream>#include<string>usingnamespacestd;classPerson{protected:stringname;longid;public:Person(string_name,long_id):name(_name),id(_id){}stringgetName()const{returnname;}longgetId()const{returnid;}};classStudent:publicPerson{private:stringclassName;intstudyTime;public:Student(string_name,long_id,string_className,int_studyTime):Person(_name,_id),className(_className),studyTime(_studyTime){}intgetStudyTime()const{returnstudyTime;}intcalculateWorkTime()const{returnstudyTime*2;}//计算学生的学习时间};classTeacher:publicPerson{private:stringdepartment;intteachingQuantity;public:Teacher(string_name,long_id,string_department,int_teachingQuantity):Person(_name,_id),department(_department),teachingQuantity(_teachingQuantity){}intgetTeachingQuantity()const{returnteachingQuantity;}intcalculateWorkTime()const{returnteachingQuantity*2;}//计算教师的工作时间};intmain(){//创建学生对象Studentstudent(\张三\1234567890,\三年级一班\10);//创建教师对象Teacherteacher(\李四\9876543210,\数学系\5);//输出学生和教师的信息cout<<\学生姓名:\<<student.getName()<<endl;cout<<\学生身份证:\<<student.getId()<<endl;cout<<\学生班级:\<<student.getClassName()<<endl;cout<<\学生学习时间:\<<student.getStudyTime()<<\小时/周\<<endl;cout<<\学生工作时间:\<<student.calculateWorkTime()<<\小时/周\<<endl;cout<<endl;cout<<\教师姓名:\<<teacher.getName()<<endl;cout<<\教师身份证:\<<teacher.getId()<<endl;cout<<\教师部门:\<<teacher.getDepartment()<<endl;cout<<\教师教学数量:\<<teacher.getTeachingQuantity()<<\节/周\<<endl;cout<<\教师工作时间:\<<teacher.calculateWorkTime()<<\小时/周\<<endl;return0;}```在这个程序中，`Person`类是学生和教师类的基类，包含姓名和身份证号两个属性。`Student`和`Teacher`类分别继承于`Person`类，并新增了自己的属性和方法。`Student`类有一个额外的属性`className`表示班级，和`studyTime`表示每周学习时间。`calculateWorkTime`方法用于计算学生的工作时间，即学习时间乘以2。`Teacher`类有一个额外的属性`department`表示部门，和`teachingQuantity`表示每周教学数量。`calculateWorkTime`方法用于计算教师的工作时间，即教学数量乘以2。在程序的`main`函数中，我们创建了一个学生对象和一个教师对象，并打印出他们的信息以及计算出的工作/学习时间。4.GiventhedefinitionofclassPointasfollows:DesignaCircleclasswiththepropertiesofacenterandaradius.Thecenterofthecirclcisapoint.TheCircleclassmustbederivedfromthePointclass.TheCircleclasscanimplementtheoperationsofcalculatingtheareaandprintingoutthecenter,radiusandarea.DesignanotherclassCylinderwiththepropertiesofabaseandaheight.Thebaseisacircle.DerivethisclassfromtheCircleclass.TheCylinderclasscanimplementtheoperationsofcalculatingthevolume,andprintingoutthebase,heightandvolume.Supposethefollowingcodeisinthemainfunction.```pythonimportmathclassPoint:def__init__(self,x=0,y=0):self.x=xself.y=yclassCircle(Point):def__init__(self,center,radius):super().__init__(center.x,center.y)self.radius=radiusdefarea(self):returnmath.pi*self.radius**2defprint_details(self):print(\CircleDetails:\print(\Center:({},{})\format(self.x,self.y))print(\Radius:{}\format(self.radius))print(\Area:{:.2f}\format(self.area()))classCylinder(Circle):def__init__(self,base_center,radius,height):super().__init__(base_center,radius)self.height=heightdefvolume(self):returnself.area()*self.heightdefprint_details(self):print(\CylinderDetails:\print(\BaseCenter:({},{})\format(self.x,self.y))print(\Radius:{}\format(self.radius))print(\Height:{}\format(self.height))print(\Volume:{:.2f}\format(self.volume()))#Exampleusage:if__name__=='__main__':c=Circle(Point(0,0),3)c.print_details()print()cy=Cylinder(Point(2,2),3,5)cy.print_details()```Thiscodedefinesa`Point`classasthebaseclass,`Circle`classderivedfrom`Point`,and`Cylinder`classderivedfrom`Circle`.The`Circle`classcalculatestheareaandprintsthedetailsofacircle,whilethe`Cylinder`classcalculatesthevolumeandprintsthedetailsofacylinder.The`main`functiondemonstratestheusageoftheseclassesbycreatingobjectsandcallingtheirrespectivemethods.5.Giventhefollowingcode:(1)CompletethedefmitionofclassEmployee.Note:employee'spayment=payRate*hoursWorked.(2)DefimeaManagerclassderivedfromclassEmployee.IthasthemembersofEmploveeanditsownmemberlevel.Note:manager'spayment=payRate*level*hoursWorked.(3)DefineanotherclassSalesmanderivedfromclassEmployee.ItalsohasthemembersofEmployee,inadditiontoitsownmembersale.Note:salesman'spayment=payRate*sale*hoursWorked.(4)TesttheManagerandSalesmanclassesbyusingabaseclasspointer.```cpp#include<iostream>usingnamespacestd;classEmployee{protected:intlevel;floatsalary;intworkHours;public:Employee(intl,floats,inth):level(l),salary(s),workHours(h){}virtualvoidcalculatePayment(){floatpayment=salary*workHours;cout<<\Employee'spayment:$\<<payment<<endl;}voiddemote(){if(level>1){level--;}cout<<\Employee'sleveldemotedto:\<<level<<endl;}};classManager:publicEmployee{private:stringemployer;public:Manager(intl,floats,inth,stringe):Employee(l,s,h),employer(e){}voidcalculatePayment(){floatpayment=salary*level*workHours;cout<<\Manager'spayment:$\<<payment<<endl;}};classSalesperson:publicEmployee{private:intsales;public:Salesperson(intl,floats,inth,intsa):Employee(l,s,h),sales(sa){}voidcalculatePayment(){floatpayment=salary*workHours+sales*0.1;cout<<\Salesperson'spayment:$\<<payment<<endl;}};intmain(){Employeeemployee(3,20,8);Managermanager(5,30,8,\ABCCompany\Salespersonsalesperson(3,15,8,1000);employee.calculatePayment();manager.calculatePayment();salesperson.calculatePayment();employee.demote();return0;}```这段代码定义了一个基类Employee，以及从该类派生的Manager和Salesperson类。Employee类有级别、工资和工作时间的成员变量，以及计算支付和降级的成员函数。Manager类还有一个雇主成员变量，并重写了计算支付的函数。Salesperson类还有销售额成员变量，并也重写了计算支付的函数。在主函数中，示例了如何创建员工、经理和销售员对象，并调用它们的计算支付函数和降级函数。输出会显示出每个类的支付金额，以及员工降级后的级别。6.Hereisaclasshierarchy,showninFigure7-5,torepresentvariousmediaobjects:GiventhedefinitionofthebaseclassMedia:(1)Explaintheclassrelationshipdescribedinthehierarchydiagram.(2)DefinetheBookandMagazineclassesaccordingtothehierarchydiagram.(Hint:Theprintfunctionofeachclassdisplaysallinformationofdatamembers.Theidfunctionofeachclassreturnsastringidentifierthatcanindicatethemediafeature.Thisidentifierconsistsofdatamembersofeachclass)(3)WritethemainfunctiontotesttheBookandMagazineclasses.(Hint:YoumustdefineapointertoaMediaobjectinthemainfunction.)略。7.DesignsaclassnamedPersonanditsderivedclassesnamedStudentandEmployee.AssumethatthedeclarationofthePersonclassisasfollows:(1)DefinethetoStringfunctioninthePersonclass.ThereturningvalueofthetoStringfunctionisusedtodisplaytheclassinformationinthefollowingformat:Name:XXXX;Address:XXXXXXX.(2)DefinetheStudentclassderivedfromthePersonclass.Astudenthasaclassstatus(freshmen,sophomore,junior,orsenior).OverridethetoStringfunctionintheStudentclass.(3)DefinetheEmployeeclassderivedfromthePersonclass.Anemployeehasanofficeandasalary.OverridethetoStringfunctionintheEmployeeclass.(4)WriteatoplevelfunctionwithaparameterofPersontypeandwritethemainfunctiontotesttheStudentandEmployeeclasses.```cpp#include<iostream>usingnamespacestd;classPerson{protected:stringname;stringaddress;public:Person(stringname=\stringaddress=\{this->name=name;this->address=address;}stringtoString(){return\Name:\+name+\;\地址:\+address+\}};classStudent:publicPerson{private:intstudentID;public:Student(stringname=\stringaddress=\intstudentID=0):Person(name,address){this->studentID=studentID;}};intmain(){Personperson(\John\\123MainSt\Studentstudent(\Alice\\456ElmSt\12345);cout<<\Person:\<<endl;cout<<person.toString()<<endl;cout<<Student:\<<endl;cout<<student.toString()<<endl;return0;}```这段代码定义了一个名为\Person\的基类及其名为\Student\的派生类。Person类有一个toString函数，用于返回格式化的类信息。Student类从Person类派生而来，并添加了一个名为studentID的新成员。在主函数中，我们创建了一个Person对象和一个Student对象，并分别输出它们的类信息。运行该程序，你将得到类似以下的输出结果：```Person:Name:John;地址:123MainSt.Student:Name:Alice;地址:456ElmSt.8.Writeaprogram.(1)AbstractbaseclassShape.(2)ClassesTriangle,SquareandCirclearederivedfromShape.(3)CalculatetheareasandperimetersofTriangle,SquareandCircle.下面是一个使用C++编写的示例程序，实现了抽象基类Shape和派生类Triangle、Square和Circle的功能。每个形状类都可以计算自身的面积和周长。请注意，代码中的计算公式可能需要根据实际情况进行更改。```cpp#include<iostream>usingnamespacestd;//抽象的基类形状classShape{public://纯虚函数，用于计算面积virtualfloatgetArea()=0;//纯虚函数，用于计算周长virtualfloatgetPerimeter()=0;};//类三角形，从形状派生classTriangle:publicShape{private:floatbase;floatheight;public://构造函数Triangle(floatbase,floatheight){this->base=base;this->height=height;}//重写计算面积的函数floatgetArea()override{return0.5*base*height;}//重写计算周长的函数floatgetPerimeter()override{//假设三角形的边长相等return3*base;}};//类方形，从形状派生classSquare:publicShape{private:floatside;public://构造函数Square(floatside){this->side=side;}//重写计算面积的函数floatgetArea()override{returnside*side;}//重写计算周长的函数floatgetPerimeter(){return4*side;}};//类圆形，从形状派生classCircle:publicShape{private:floatradius;constfloatpi=3.14159;//假设圆周率为3.14159public://构造函数Circle(floatradius){this->radiusradius;}//重写计算面积的函数floatgetArea()override{returnpi*radius*radius;}//重写计算周长的函数floatgetPerimeter()override{return2*pi*radius;}};intmain(){//创建三个形状对象Triangletriangle(5,8);Squaresquare(4);Circlecircle(3);//输出每个形状的面积和周长cout<<\Triangle:Area=\<<triangle.getArea()<<\Perimeter=\<<triangle.getPerimeter()<<endl;cout<<\Square:Area=\<<square.getArea()<<\Perimeter=\<<square.getPerimeter()<<endl;cout<<\Circle:Area=\<<circle.getArea()<<\Perimeter=\<<circle.getPerimeter()<<endl;return0;}```这个程序定义了一个抽象基类Shape，以及派生类Triangle、Square和Circle。每个派生类实现了Shape基类中的纯虚函数getArea()和getPerimeter()，并提供了自己的实现。在主函数中，我们创建了一个Triangle对象、一个Square对象和一个Circle对象，并使用它们的成员函数分别计算和输出面积和周长。9.Designaclasshierarchyasfollows;(1)AbaseclassShapewithvirtualfunctionprint.(2)ClassesTwoDShapeandThreeDShapederivedfromShape.TivoDShapehasvirtualfunctionsareaandperimeter:ThreeDShapehasvirtualfunctionvolume.(3)ClassesTriangle,SquareandCirclearederivedfromTwoDShape.(4)ClassesCube,CuboidandSpherearederivedfromThreeDShape.Overridethedefinitionoftheprintfunctionofeachderivedclass.Testthehierarchybyusingthemainfunctionandatop-levelfunctionwithapointertoclassShape.```cpp#include<iostream>usingnamespacestd;//基类形状classShape{public:virtualvoidprint()=0;//虚拟函数打印};//二维形状类classTwoDShape:publicShape{public:virtualfloatarea()=0;//虚拟函数计算面积virtualfloatperimeter()=0;//虚拟函数计算周长};//三维形状类classThreeDShape:publicShape{public:virtualf