/*

定义Boat与Car两个类，二者都有weight属性，

定义二者的一个友元函数totalWeight()为外部函数,

计算二者的重量和。

*/

#include<iostream>

#include<string>

using namespace std;

class Boat;

class Car {

private:

    double weight;

public:

    Car(double wg) {

        this->weight = wg;

    }

    Car(Car &tp) {

        this->weight = tp.weight;

    }

    double getWeight() {

        return weight;

    }

    ~Car() {

    }

    void show() {

        cout << "This is a Car:" << endl;

        cout << "Weight:" << weight << endl;

    }

};

class Boat {

private:

    double  weight;

public:

    Boat(double wg) {

        this->weight = wg;

    }

    Boat(Boat &tp) {

        this->weight = tp.weight;

    }

    double getWeight() {

        return weight;

    }

    ~Boat()

    {

    }

    friend double totalWeight(Boat &a, Car &b);

    void show() {

        cout << "This is a Boat:" << endl;

        cout << "Weight:" << weight << endl;

    }

};

double totalWeight(Boat &a, Car &b) {

    return a.getWeight() + b.getWeight();

}

int main() {

    Boat a(1024.0);

    Car b(1024.0);

    a.show();

    b.show();

    cout << "The total weight of the Car and the Boat:" << endl;

    cout << totalWeight(a, b);

    return 0;

}

• 测试截图