exercise14_2.h

#ifndef CP5_CH14_EX14_02_H
#define CP5_CH14_EX14_02_H

#include <string>
#include <iostream>

class Sales_data
{
	friend std::istream& operator>>(std::istream&, Sales_data&); // input
	friend std::ostream& operator<<(std::ostream&, const Sales_data&); // output
	friend Sales_data operator+(const Sales_data&, const Sales_data&); // addition

public:
	Sales_data(const std::string &s, unsigned n, double p) :bookNo(s), units_sold(n), revenue(n*p) {}
	Sales_data() : Sales_data("", 0, 0.0f) {}
	Sales_data(const std::string &s) : Sales_data(s, 0, 0.0f) {}
	Sales_data(std::istream &is);

	Sales_data& operator+=(const Sales_data&); // compound-assignment
	std::string isbn() const { return bookNo; }

private:
	inline double avg_price() const;

	std::string bookNo;
	unsigned units_sold = 0;
	double revenue = 0.0;
};

std::istream& operator>>(std::istream&, Sales_data&);
std::ostream& operator<<(std::ostream&, const Sales_data&);
Sales_data operator+(const Sales_data&, const Sales_data&);

inline double Sales_data::avg_price() const
{
	return units_sold ? revenue / units_sold : 0;
}

#endif // CP5_CH14_EX14_02_H