task2.cpp

#include <iostream>
#include <typeinfo>

// definitation of Graph
class Graph
{
public:
    virtual 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);
}

改动前的结果：

 改动后的结果：

同名覆盖原则：派生类与基类中有相同成员时，若未强行指明，则通过派生类对象使用的是派生类的同名成员；如果要通过派生类的对象访问基类被覆盖的同名成员，则需要加对象名.基类名::同名成员来限定；
二元作用域分辨符：在多重继承的情况下，如果两个基类中存在相同的变量名，可以使用作用域运算符来进行区分；
类型兼容原则：指在需要基类对象的任何地方，都可以使用公有派生类的对象来替代。通过公有继承，派生类得到了基类中除构造函数、析构函数之外的所有成员。

task3

battery.hpp

#include<iostream>
using namespace std;
class Battery
{
public: 
    Battery(int ca=70):capacity(ca){};
    int get_capacity()
    {
        return capacity;
    }
private:
    int capacity;
};

car.hpp

#include<iostream>
#include<string>
#include<iomanip>
using namespace std;
class Car
{
public: 
    Car(string n_maker,string n_model,int n_year,int n_odometers=0):maker(n_maker),model(n_model),year(n_year),odometers(n_odometers){};
    void info()
    {
        cout<<"maker:     "<<maker<<endl;
        cout<<"model:     "<<model<<endl;
        cout<<"year:      "<<year<<endl;
        cout<<"odometers: "<<odometers<<endl;
    }
    void update_odometers(int n)
    {
        if(n<odometers)
            cout<<"更新数据有误！"<<endl;
        else
            odometers=n; 
    }
private:
    string maker;
    string model;
    int year;
    int odometers;
};

electricCar.hpp

#include<iostream>
#include"car.hpp"
#include"battery.hpp"
using namespace std;
class electricCar:public Car
{
public:
    electricCar(string n_maker,string n_model,int n_year,int n_odometers=0,Battery b=70):Car(n_maker,n_model,n_year,n_odometers),battery(b){};
    void info()
    {
        Car::info(); 
        cout<<"capacity:  "<<battery.get_capacity()<<endl;
    }
private:
    Battery battery;
};

task3.cpp

#include <iostream>
#include "electricCar.hpp"
int main()
{
    using namespace std;
    
    // test class of Car
    Car oldcar("Au", "a2", 2021);
    cout << "--------oldcar's info--------" << endl;
    oldcar.update_odometers(20000);
    oldcar.info();
    
    cout << endl;
    
    // test class of ElectricCar
    electricCar newcar("Tesla", "model s", 2016);
    newcar.update_odometers(2500);
    cout << "\n--------newcar's info--------\n";
    newcar.info();
}

 task4

pets.hpp

#include<iostream>
#include<string>
using namespace std;
class MachinePets
{
public:
    MachinePets(const string s):nickname(s){};
    virtual string talk()=0;
    string get_nickname()const
    {
        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~";
    }
};

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);
}