实验四 类的继承、派生和多态（1）

一、实验内容

1、车辆基本信息管理

基于Car类派生出ElectricCar类、派生类ElectricCar中新增数据成员Battery类对象。

#ifndef BATTERY_H
#define BATTERY_H

class Battery {
public:
    Battery(int batterySize0=70);
    int getSize();
private:
    int batterySize;
};


#endif

#ifndef CAR_H
#define CAR_H

#include<string>
#include<iostream>
using std::string;
using std::ostream;

class Car {
public:
    Car(string maker0, string model0, int year0, int odometer0=0);
    void updateOdometer(int odometerN);
    friend ostream & operator<<(ostream &out, const Car &c);
private:
    string maker;
    string model;
    int year;
    int odometer;
};


#endif

#ifndef ELECTRIC_H
#define ELECTRIC_H

#include"battery.h"
#include"car.h"

class ElectricCar:virtual public Car{
public:
    ElectricCar(string maker0,string model0,int year0,int odometer0=0);
    friend ostream & operator<<(ostream &out, const ElectricCar &c);
private:
    Battery battery;
};


#endif

#include"battery.h"
#include<iostream>

using std::cout;
using std::endl;

Battery::Battery(int batterySize0 ):batterySize(batterySize0) {
}

int Battery::getSize(){
    return batterySize;
}

#include"car.h"
#include<iostream>

using std::cout;
using std::endl;

Car::Car(string maker0, string model0, int year0, int odometer0 ) :maker(maker0), model(model0), year(year0), odometer(odometer0) {
}

void Car::updateOdometer(int odometerN) {
    if (odometerN < odometer) {
        cout << "WRONG DATA!";
        exit(0);
    }
    else odometer = odometerN;
}
ostream & operator<<(ostream &out, const Car &c) {
    cout << "maker:" << c.maker << endl;
    cout << "model:" << c.model << endl;
    cout << "year:" << c.year << endl;
    cout << "odometer:" << c.odometer << endl;
    return out;
}

#include"electriccar.h"
#include<iostream>

using std::cout;
using std::endl;

ElectricCar::ElectricCar(string maker0, string model0, int year0, int odometer0 ):Car(maker0,model0,year0,odometer0) {
}

ostream & operator<<(ostream &out, const ElectricCar &c) {
    Car a(c);
    cout<<a<<endl;
    Battery m=c.battery;
    cout << "batterySize:" <<m.getSize()<<"-kWh"<< endl;
    return out;
}

#include <iostream>
using namespace std;

#include "car.h"
#include "electriccar.h" 

int main() {
    // 测试Car类 
    Car oldcar("Audi","a4",2016);
    cout << "--------oldcar's info--------" << endl;
    oldcar.updateOdometer(25000);
    cout << oldcar << endl;

    // 测试ElectricCar类 
    ElectricCar newcar("Tesla","model s",2016);
    newcar.updateOdometer(2500);
    cout << "
--------newcar's info--------
"; 
    cout << newcar << endl;

    system("pause");
    
    return 0;
}

效果如下：

2、补足程序

重载运算符[]为一维动态整形数组类ArrayInt的成员函数，使得通过动态整形数组对象名和下标可以 访问对象中具体元素。

#ifndef ARRAY_INT_H
#define ARRAY_INT_H

class ArrayInt{
    public:
        ArrayInt(int n, int value=0);
        ~ArrayInt();
        // 补足:将运算符[]重载为成员函数的声明
        // ×××
        int& operator[](int i);
        void print(); 
    private:
        int *p;
        int size;
};

#endif

#include "arrayInt.h"
#include <iostream>
#include <cstdlib>
using std::cout;
using std::endl;

ArrayInt::ArrayInt(int n, int value): size(n) {
    p = new int[size];
    
    if (p == nullptr) {
        cout << "fail to mallocate memory" << endl;
        exit(0); 
    } 
    
    for(int i=0; i<size; i++)
        p[i] = value;
}

ArrayInt::~ArrayInt() {
    delete[] p;
}

void ArrayInt::print() {
    for(int i=0; i<size; i++)
        cout << p[i] << " ";
    cout << endl;
}

// 补足:将运算符[]重载为成员函数的实现
// ×××
int & ArrayInt::operator[](int i){
    return p[i];
}

#include <iostream>
using namespace std;

#include "arrayInt.h"

int main() {
    // 定义动态整型数组对象a，包含2个元素，初始值为0
    ArrayInt a(2);
    a.print();
    
    // 定义动态整型数组对象b，包含3个元素，初始值为6
    ArrayInt b(3, 6);
    b.print();

    // 通过对象名和下标方式访问并修改对象元素
    b[0] = 2;
    cout << b[0] << endl;
    b.print();

    system("pause");

    return 0;
}

效果如下：

二、实验小结

虽然测试出结果，有几点还是不太懂：

• electriccar.cpp中，Car a(c); 我将ElectricCar类c赋值给Car类a,这是反复试探的结果，虽然意外成功，还是不太理解；
• 什么时候用&也不是很清楚。不对了，就加上&试试，偶尔可以猜对，却不是理解后的结果。

希望大佬不吝赐教，万分感激。

三、实验评论

1. https://www.cnblogs.com/xuexinyu/p/10889782.html#4272146
2. https://www.cnblogs.com/wjh1022/p/10890196.html#4272129
3. https://www.cnblogs.com/jessi-wu1005/p/10889219.html#4272106