task2

程序源码

#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);

 

未修改前截图

 

修改后截图

 

总结:

同名覆盖原则:派生类与基类中有相同成员时 ,若未强行指名,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,需要加 对象名.基类名::同名成员 。

作用域运算符(::)的作用:
1.存在具有相同名称的局部变量时,访问全局变量。

2.在类之外定义类相关函数。
3.访问类的静态变量。
4.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。
5.限定成员函数所属的类。

类型兼容原则:类型兼容原则是指在需要基类对象的任何地方,都可以使用共有派生类的对象来替代。

类型兼容规则中所指的替代包括以下的情况:

1.派生类的对象可以赋值给基类对象

2.派生类的对象可以初始化基类的引用。

3.派生类对象的地址可以赋值给基类的指针。

 

task3

Car.hpp

#ifndef Car_HPP
#define Car_HPP
#include<iostream>
#include<string>
using namespace std;
class Car
{
    private:
        string maker,model;
        int year,odometers;
    public:
        Car(string a,string b,int c,int d=0):maker(a),model(b),year(c),odometers(0) {};
        void info();
        void update_odometers(int x);
};

void Car::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 Car::update_odometers(int x)
{
    if(x<odometers)
    cout<<"更新数值有误!"<<endl;
    else
    odometers=x;
}
#endif

Battery.hpp

#ifndef Battery_HPP
#define Battery_HPP
#include<iostream>
using namespace std;
class Battery
{
    private:
        int capacity;
    public:
        Battery(int x=70):capacity(x) {};
        int get_capacity() const {return capacity;}
};
#endif

ElectricCar.hpp

#ifndef ElectricCar_Hpp
#define ElectricCar_Hpp
#include<iostream>
#include<string>
#include"Car.hpp"
#include"Battery.hpp"
using namespace std;
class ElectricCar: public Car
{
    private:
        Battery battery;
    public:
        ElectricCar(string a, string b, int c, int d=70): Car(a,b,c),battery(d) {};
        void info();
        ~ElectricCar(){};
     
}; 

void ElectricCar::info()
{
     Car::info();
     cout<<"capacity:\t"<<battery.get_capacity()<<"-kwh"<<endl;
}
#endif

task3.cpp

#include <iostream>
#include"ElectricCar.hpp"
int main()
{
    using namespace std;

    // test class of Car
    Car oldcar("AAA", "a3", 2021);
    cout << "--------oldcar's info--------" << endl;
    oldcar.update_odometers(27000);
    oldcar.info();

    cout << endl;

    // test class of ElectricCar
    ElectricCar newcar("SSS", "model s", 2021);
    newcar.update_odometers(2700);
    cout << "\n--------newcar's info--------\n";
    newcar.info();
}

 

task4

pets.hpp

#ifndef pets_HPP
#define pets_HPP
#include<iostream>
#include<string>
using namespace std;
class MachinePets
{
    private:
        string nickname;
    public:
        MachinePets(const string s):nickname(s) {}
        virtual string talk();
        string get_nickname() {return nickname;}
};
string MachinePets::talk() { return "Hello";}

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

pets.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);
}

 

posted on 2021-11-30 23:41  Polaris啊  阅读(29)  评论(2编辑  收藏  举报