实验四（继承）

task2.1:

#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);
}

 task2.2:

#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);
}

　　同名覆盖原则：当派生类与基类中有相同成员时，若未强行命名，则通过派生类对象使用的是派生类的同名成员。

　　二元作用域分辨运算符：1.若成员函数中定义了和类域中的变量同名的变量，则类域中的变量被块作用域中的变量隐藏。这时可以在变量名前加类名和作用域运算符（：：）访问这种隐藏变量。2.可以用一元作用域运算符访问隐藏的全局变量。3.定义类中声明的成员函数时可以用类名和二元作用域运算符（：：），将每个成员函数绑定到声明成员函数与数据成员的类定义上。

　　类型兼容原则：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代替。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。这样，共有派生类实际就具备了基类的所有功能，凡是基类能解决的问题，公有派生类都可以解决。

electricCar.hpp

#include<iostream>
#include<string>
using namespace std;
class Car {
public:
    Car(string ma, string mo, int y, int o = 0) :maker(ma), model(mo), year(y), odometers(o) {}
    void info() {
        cout << "maker:\t\t\t" << maker << endl;
        cout << "model:\t\t\t" << model << endl;
        cout << "year:\t\t\t" << year << endl;
        cout << "odometers:\t\t" << odometers << endl;
    }
    void update_odometers(int n) {
        if (n >= odometers) odometers = n;
        else cout << "Wrong data" << endl;
    }
private:
    string maker;
    string model;
    int year;
    int odometers;
};

class Battery {
public:
    Battery(int c = 70) :capacity(c) {}
    int get_capacity() {
        return capacity;
    }
private:
    int capacity;
};

class ElectricCar:public Car {
public:
    ElectricCar(string ma, string mo, int y, Battery ba=(70), int o = 0) :Car(ma,mo,y,o),battery(ba) {}
    void info() {
        Car::info();
        cout << "capacity:\t\t" << battery.get_capacity() <<"-kWh"<< endl;
    }
private:
    Battery battery;
};

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("Tesla", "model s", 2021);
    newcar.update_odometers(2500);
    cout << "\n--------newcar's info--------\n";
    newcar.info();
}

 pets.hpp

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

class PetCats :public MachinePets {
public:
    PetCats(const string s) :MachinePets(s) {}
    virtual string talk() {
        return "miao wu~";
    }
};

class PetDogs :public MachinePets {
public:
    PetDogs(const string s) :MachinePets(s) {}
    virtual 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);
}