//定义一个将两个sales_item对象相加的非成员函数。
#include <iostream>
#include<string>
using namespace std;


class sales_item
{
    //将Add函数声明为sales_item的友元。
    friend sales_item Add(const sales_item& obj1,const sales_item& obj2);
    public:
    sales_item(const string &book="fuck!"):isbn(book),units_sold(0),revenue(0.0)
    {

    }
    sales_item(istream &is=cin)
    {
        cin >> isbn >> units_sold >> revenue;

    }
    void print()
    {
        std::cout<<isbn<<"  "<<units_sold<<"  "<<revenue<<endl;
    }
    private:
        int units_sold;
        double revenue;
        string isbn;
};
//Add函数执行相加操作。
sales_item Add(const sales_item &obj1,const sales_item &obj2);
sales_item Add(const sales_item &obj1,const sales_item &obj2)
{
    sales_item  temp;
    temp.isbn=obj1.isbn;
    temp.units_sold=obj1.units_sold+obj2.units_sold;
    temp.revenue=obj1.revenue+obj2.revenue;
    return temp;

}


int main()
{
    sales_item s1(cin);
    sales_item s2(cin);
    s1.print();
    s2.print();
    cout<<endl;
    sales_item item3;
    item3=Add(const& s1,const& s2);
    return 0;
}