C++重要题目一

#include<iostream>
class Boat;//必须事先声明
class Car
{
    int size;
public:
    void setSize(int j){size=j;}
    int getSize(){return size;}
    friend int leisure(int time,Car& aobj,Boat& bobj);
};
class Boat:Car//此处的Car可要可不要
{
    int size;
public:
    void setSize(int j){size=j;}
    int getSize(){return size;}
    friend int leisure(int time,Car& aobj,Boat& bobj);
};
int leisure(int time,Car& aobj,Boat& bobj)
{
    return time*aobj.size*bobj.size;
}
int main()
{
    Car c1;
    c1.setSize(2);
    Boat b1;
    b1.setSize(3);
    std::cout<<leisure(5,c1,b1)<<std::endl;
    system("pause");
}