ch15/1535ex/Basket2.cc
// calculate and print price for given number of copies, applying any discounts 
calculate and print price for given number of copies, applying any discounts
calculate and print price for given number of copies applying any discounts
void print_total(ostream &os, 
                 const Item_base &item, size_t n)
{
    os << "ISBN: " << item.book() 
       << "\tnumber sold: " << n << "\ttotal price: "
       << item.net_price(n) << endl;
}
void print_total ( ostream & os , const Item_base & item , size_t n ) { os << " " << item . book ( ) << " \t " << n << " \t " << item . net_price ( n ) << endl ; }
calculate and print price for given number of copies, applying any discounts
calculate and print price for given number of copies applying any discounts
// calls Item_base::book // virtual call: which version of net_price to call is resolved at run time