摘要：
#include<iostream>class Sales_item{ friend std::istream& operator>>(std::istream&, Sales_item&); friend std::ostream& operator<<(std::ostream&, const Sales_item&);private: int a;public: Sales_item(int b):a(b){}; Sales_item():a(0){}; //Sales_item operator +(c 阅读全文
