Ultimately, we want
Sales_data to support the same set of operations as the
Sales_item class. The
Sales_item class had one member function (§ 1.5.2, p. 23), named
isbn, and supported the
+=, <<, and
We’ll learn how to define our own operators in Chapter 14. For now, we’ll define ordinary (named) functions for these operations. For reasons that we will explain in § 14.1 (p. 555), the functions that do addition and IO will not be members of
Sales_data. Instead, we’ll define those functions as ordinary functions. The function that handles compound assignment will be a member, and for reasons ...