C++ Primer（第5版） 練習 14.20

練習 14.20 為你的Sales_data類定義加法和復合賦值運算符。

環境：Linux Ubuntu（云服務器）

工具：vim

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代碼塊

struct Sales_data{Sales_data(const string &s, unsigned n, double p):bookNo(s), units_sold(n), price(p), revenue(p * n) {}Sales_data(): Sales_data("", 0, 0) {}Sales_data(string s): Sales_data(s, 0, 0) {}friend istream &operator>>(istream &, Sales_data &);friend ostream &operator<<(ostream &, const Sales_data &);Sales_data& operator+(const Sales_data &, const Sales_data &);Sales_data& operator+= (const Sales_data &);string isbn() const;Sales_data& combine(const Sales_data&);double avg_price() const;string bookNo;unsigned units_sold = 0;double price = 0.0;double revenue = 0.0;
};Sales_data& Sales_data::operator+(const Sales_data &lhs, const Sales_data &rhs){units_sold = lhs.units_sold + rhs.units_sold;revenue = lhs.revenue + rhs.revenue;return *this;
}Sales_data& Sales_data::operator+=(const Sales_data &rhs){units_sold += rhs.units_sold;revenue += rhs.revenue;return *this;
}