ex7_26.h

//
//  ex7_26.h
//  Exercise 7.26
//
//  Created by pezy on 11/14/14.
//  Copyright (c) 2014 pezy. All rights reserved.
//
//  @See ex7_21.h
//  @Add inline member function "Sales_data::avg_pric" 

#ifndef CP5_ex7_26_h
#define CP5_ex7_26_h

#include <string>
#include <iostream>

class Sales_data {
    friend std::istream &read(std::istream &is, Sales_data &item);
    friend std::ostream &print(std::ostream &os, const Sales_data &item);
    friend Sales_data add(const Sales_data &lhs, const Sales_data &rhs);

public:
    Sales_data() = default;
    Sales_data(const std::string &s):bookNo(s) {}
    Sales_data(const std::string &s, unsigned n, double p):bookNo(s),units_sold(n),revenue(n*p){}
    Sales_data(std::istream &is) { read(is, *this); }

    std::string isbn() const { return bookNo; };
    Sales_data& combine(const Sales_data&);
    
private:
    inline double avg_price() const;        

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

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

// declarations for nonmember parts of the Sales_data interface.
std::istream &read(std::istream &is, Sales_data &item);
std::ostream &print(std::ostream &os, const Sales_data &item);
Sales_data add(const Sales_data &lhs, const Sales_data &rhs);

#endif