用C++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(),计算二者的重量和

#include <iostream>
#include <bits/stdc++.h>
using namespace std;
class cat;
class Boat;
class Boat
{
    private:
        int weight;
    public:
        void getwei(int t)
        {
            weight=t;
        }
        friend void getweight(Boat a,cat b); // 定义getweight为友元函数，为后面调用做准备
};
class cat
{
    private:
        int weight;
    public:
        void getwei(int t)
        {
            weight=t;
        }
        friend void getweight(Boat a,cat b);//如上
};
void getweight(Boat a,cat b)
{
    int w=a.weight+b.weight;//由于是getweight是友元函数，所以可以直接调用boat和cat类中的私有成员
    printf("%d\n",w);
}
int main()
{
    Boat a;
    a.getwei(10);
    cat b;
    b.getwei(5);
    getweight(a,b);
    return 0;
}