ex7_26_sales_data.cpp

#include "ex7_26_sales_data.h"

// member functions.
Sales_data& Sales_data::combine(const Sales_data& rhs)
{
    units_sold += rhs.units_sold;
    revenue += rhs.revenue;
    return *this;
}

// friend functions
std::istream& read(std::istream& is, Sales_data& item)
{
    double price = 0;
    is >> item.bookNo >> item.units_sold >> price;
    item.revenue = price * item.units_sold;
    return is;
}

std::ostream& print(std::ostream& os, const Sales_data& item)
{
    os << item.isbn() << " " << item.units_sold << " " << item.revenue;
    return os;
}

Sales_data add(const Sales_data& lhs, const Sales_data& rhs)
{
    Sales_data sum = lhs;
    sum.combine(rhs);
    return sum;
}