实验四 继承

1.实验任务2

验证性实验。

在C++编码环境中，输入task2.cpp。

task2.cpp:

#include <iostream>
#include <typeinfo>

// definitation of Graph
class Graph
{
public:
    void draw() { std::cout << "Graph::draw() : just as an interface\n"; }
};


// definition of Rectangle, derived from Graph
class Rectangle : public Graph
{
public:
    void draw() { std::cout << "Rectangle::draw(): programs of draw a rectangle\n"; }
};


// definition of Circle, derived from Graph
class Circle : public Graph
{
public:
    void draw() { std::cout << "Circle::draw(): programs of draw a circle\n"; }
};


// definitaion of fun(): as a call interface
void fun(Graph *ptr)
{
    std::cout << "pointer type: " << typeid(ptr).name() << "\n";
    std::cout << "RTTI type: " << typeid(*ptr).name() << "\n";
    ptr -> draw();
}

// test 
int main()
{
    Graph g1;
    Rectangle r1;
    Circle c1;

    // call by object name
    g1.draw();
    r1.draw();
    c1.draw();

    std::cout << "\n";

    // call by object name, and using the scope resolution operator::
    r1.Graph::draw();
    c1.Graph::draw();

    std::cout << "\n";

    // call by pointer to Base class
    fun(&g1);
    fun(&r1);
    fun(&c1);
}

运行结果截图：

 

添加virtual后的运行结果截图：

 

 归纳总结：

a.同名覆盖原则：

派生类与基类中有相同成员时，通过派生类对象使用的是派生类的同名成员；

可以通过对象名.基类名::同名成员的方式，访问基类被覆盖的同名成员。

b.二元作用域分辨符：

可以告之编译器成员属于哪个类。

c.类型兼容原则：

1.派生类的对象可以隐含转换为基类的对象。
2.派生类的对象可以初始化基类的引用。
3.派生类的指针可以隐含转化为基类的指针。

2.实验任务3

程序包括Battery.hpp, Car.hpp, ElectricCar.hpp, task3.cpp。

Battery.hpp：

#ifndef BATTERY_HPP
#define BATTERY_HPP
#include <iostream>
using std::cout;
using std::endl;
class Battery {
public:
    Battery(int n=70) :capacity(n) {};
    double get_capacity() const { return capacity; }
    ~Battery() {};
private:
    double capacity;

};


#endif

Car.hpp：

#ifndef CAR_HPP
#define CAR_HPP
#include <iostream>

using namespace std;
class Car {
public:
    Car(string a, string b, int c, double d = 0) :maker(a), model(b), year(c), odometers(d) {};
    void info()
    {
        cout << "maker:\t\t" << maker << endl;
        cout << "model\t\t" << model << endl;
        cout << "year:\t\t" << year << endl;
        cout << "odometers:\t" << odometers << endl;
    }
    void update_odometers(double n) ;
    ~Car() {};

private:
    string maker, model;
    int year;
    double odometers;

};

void Car::update_odometers(double n)
{
    if (n > odometers)
        odometers = n;
    else cout << "更新数值有误" << endl;
}

#endif

ElectricCar.hpp：

#ifndef ELECTRICCAR_HPP
#define ELECTRICCAR_HPP
#include "car.hpp"
#include "battery.hpp"
#include<iostream>
using namespace std;
class ElectricCar: public Car {
public:
    ElectricCar(string a, string b, int c, int  d = 70) :Car(a, b, c), battery(d) {};
    void info() {
        Car::info();
        cout << "capacity:\t" << battery.get_capacity() <<"-kwh" << endl;
    }
    ~ElectricCar() {};
private:
    Battery battery;



};

#endif

 

task3.cpp：

#include <iostream>
#include "electricCar.hpp"

int main()
{
    using namespace std;

    // test class of Car
    Car oldcar("Audi", "a4", 2016);
    cout << "--------oldcar's info--------" << endl;
    oldcar.update_odometers(25000);
    oldcar.info();

    cout << endl;

    // test class of ElectricCar
    ElectricCar newcar("legion", "b5", 2020);
    newcar.update_odometers(4396);
    cout << "\n--------newcar's info--------\n";
    newcar.info();
}

运行截图：

 

 3.实验任务4

程序包括pets.hpp, task4.cpp。

pets.hpp:

#ifndef PETS_HPP
#define PETS_HPP
#include <iostream>
using namespace std;
class MachinePets {
public:
        MachinePets(const string s):nickname(s) {};
        virtual  string talk() { return "1"; }
        string get_nickname() { return nickname; }
private:
    string nickname;
};
class PetCats:public MachinePets {
public:
    PetCats(const string s) :MachinePets(s) {};
    string talk() {
        return "miao wu~";
    }
};
class PetDogs :public MachinePets {
public:
    PetDogs(const string s) :MachinePets(s) {};
    string talk() {
        return "wang wang~";
    }
};



#endif

 

task4.cpp:

#include <iostream>
#include "pets.hpp"

void play(MachinePets *ptr)
{
    std::cout << ptr->get_nickname() << " says " << ptr->talk() << std::endl;
}

int main()
{
    PetCats cat("miku");
    PetDogs dog("da huang");

    play(&cat);
    play(&dog);
}

运行截图：