14.1

14.1
内置运算符有明确的定义
而重载的运算符的功能有你重载的版本决定

当你重载的运算符和内置的含义和用法是一样的，那么可以认为它们是一样的

14.2

Sales_data& Sales_data::operator+=(const Sales_data &rhs)
{
    units_sold += rhs.units_sold;
    revenue += rhs.revenue;
    return *this;
}

std::istream& operator>>(std::istream &is, Sales_data &item)
{
    double price = 0.0;
    is >> item.bookNo >> item.units_sold >> price;
    if (is)
        item.revenue = price * item.units_sold;
    else
        item = Sales_data();
    return is;
}

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

Sales_data operator+(const Sales_data &lhs, const Sales_data &rhs)
{
    Sales_data sum = lhs;
    sum += rhs;
    return sum;
}

14.3

(a) "cobble" == "stone" // 都不是
(b) svec1[0] == svec2[0] //string
(c) svec1 == svec2   //vector
(d) "svec1[0] == "stone"  // 是否多了一个引号？

14.4

(a) %   //非成员
(b) %=  //成员
(c) ++  //成员
(d) ->  //成员
(e) <<  //非成员
(f) &&  //非成员
(g) ==  //非成员
(h) ()  //成员

14.5

std::istream& operator>>(std::istream &in, Book &book)
{
    in >> book.no_ >> book.name_ >> book.author_ >> book.pubdate_;
    return in;
}

std::ostream& operator<<(std::ostream &out, const Book &book)
{
    out << book.no_ << " " << book.name_ << " " << book.author_ << " " << book.pubdate_;
    return out;
}

bool operator==(const Book &lhs, const Book &rhs)
{
    return lhs.no_ == rhs.no_;
}

bool operator!=(const Book &lhs, const Book &rhs)
{
    return !(lhs == rhs);
}