C++Primer第一章例题及练习题答案源代码

#include "Sales_item.h" #include <iostream> using namespace std; // assumes that both objects refer to the same isbn Sales_item& Sales_item::operator+=(const Sales_item& rhs) { units_sold += rhs.units_sold; revenue += rhs.revenue; return *this; } // assumes that both objects refer to the same isbn Sales_item operator+(const Sales_item& lhs, const Sales_item& rhs) { Sales_item ret(lhs); // copy lhs into a local object that we'll return ret += rhs; // add in the contents of rhs return ret; // return ret by value } istream& operator>>(istream& in, Sales_item& s) { double price; in >> s.isbn >> s.units_sold >> price; // check that the inputs succeeded if (in) s.revenue = s.units_sold * price; else s = Sales_item(); // input failed: reset object to default state return in; } ostream& operator<<(ostream& out, const Sales_item& s) { out << s.isbn << "\t" << s.units_sold << "\t" << s.revenue << "\t" << s.avg_price(); return out; } double Sales_item::avg_price() const { if (units_sold) return revenue/units_sold; else return 0; }