类的成员函数

#include <iostream>#include <string>using namespace std;class Sales_item  // class要变成对象才能用，{public:double avg_price() const; // 函数原型声明，bool same_isbn(const Sales_item &rhs) const  // 公有类的成员函数有const则不能变，{return isbn == rhs.isbn;// return this -> isbn == rhs.isbn;}   // private:  // 私有的，public:   // 共有的，std::string isbn;unsigned untis_sold;double revenue;};double Sales_item::avg_price() const{if(this->units_sold)return (this->units_sold);  //return (this->revenue),elsereturn 0;}int main (){    Sales_item item1,item2;item1.isbn = "0-201-78345-X";item1.untis_sold = 10;item1.revenue = 300.00;cout << item1.avg_price() << endl;        item2.isbn = "0-201-78345-X";item2.untis_sold = 2;item2.revenue = 70.00;cout << item2.avg_price() << endl;if(item1.same_isbn(item2))         cout << "这两个Sales item 是同一种书！" << endl;elsecout << "这两个Sales item 不是同一种书！" << endl;return 0;}