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#include <iostream>
#include <string>

class Sales_item {
friend bool operator==(const Sales_item&, const Sales_item&);
// other members as before
public:
    // added constructors to initialize from a string or an istream
    Sales_item(const std::string &book):
              isbn(book), units_sold(0), revenue(0.0) { }
    Sales_item(std::istream &is)
 {
  is >> *this;
 }
    friend std::istream& operator>>(std::istream&, Sales_item&);
    friend std::ostream& operator<<(std::ostream&, const Sales_item&);
public:
    // operations on Sales_item objects
    // member binary operator: left-hand operand bound to implicit this pointer
    Sales_item& operator+=(const Sales_item&);
    // other members as before
   
public:
    // operations on Sales_item objects
    double avg_price() const;
    bool same_isbn(const Sales_item &rhs) const
        { return isbn == rhs.isbn; }
    // default constructor needed to initialize members of built-in type
    Sales_item(): units_sold(0), revenue(0.0) { }
// private members as before
private:
    std::string isbn;
    unsigned units_sold;
    double revenue;

};

// nonmember binary operator: must declare a parameter for each operand
Sales_item operator+(const Sales_item&, const Sales_item&);

inline bool
operator==(const Sales_item &lhs, const Sales_item &rhs)
{
    // must be made a friend of Sales_item
    return lhs.units_sold == rhs.units_sold &&
           lhs.revenue == rhs.revenue &&
    lhs.same_isbn(rhs);
}

inline bool
operator!=(const Sales_item &lhs, const Sales_item &rhs)
{
    return !(lhs == rhs); // != defined in terms of operator==
}

using std::istream; using std::ostream;

// assumes that both objects refer to the same isbn
inline
Sales_item& Sales_item::operator+=(const Sales_item& rhs)
{
    units_sold += rhs.units_sold;
    revenue += rhs.revenue;
    return *this;
}

// assumes that both objects refer to the same isbn
inline
Sales_item
operator+(const Sales_item& lhs, const Sales_item& rhs)
{
    Sales_item ret(lhs);  // copy lhs into a local object that we'll return
    ret += rhs;           // add in the contents of rhs
    return ret;           // return ret by value
}

inline istream& operator>>(istream& in, Sales_item& s)
{
    double price;
    in >> s.isbn >> s.units_sold >> price;
    // check that the inputs succeeded
    if (in)
        s.revenue = s.units_sold * price;
    else
        s = Sales_item();  // input failed: reset object to default state
    return in;
}

inline ostream& operator<<(ostream& out, const Sales_item& s)
{
    out << s.isbn << "\t" << s.units_sold << "\t"
        << s.revenue << "\t" <<  s.avg_price();
    return out;
}

inline
double Sales_item::avg_price() const
{
    if (units_sold)
        return revenue/units_sold;
    else
        return 0;
}

 // list 容器中
list <String> &getstdcin()
{
     list <String> lst;
  if(!lst.empty())
   {
   list<String>::reference val=*lst.begin(); //引用
   lst.erase(index-1);
   return lst.at(index);  //返回下标为index 的引用
   }
         String word;
         list<String>::iterator iter= lst.begin(); //list 迭代器只能自增，自减不等操作，不支持算术和关系运算
       while(cin>>word)
     {
       iter=lst.insert(lst,word);
     }
}

 

#include <string>
#include <iostream>

class Screen {
public:
    // interface member functions
    typedef std::string::size_type index;
    char get() const
 {
  return contents[cursor];
 }
    inline char get(index ht, index wd) const;
    Screen(index ht = 0, index wd = 0): contents(ht * wd, ' '), cursor(0), height(ht), width(wd) { }
    Screen& move(index r, index c);
    Screen& set(char);
    Screen& set(index, index, char);
    // display overloaded on whether the object is const or not
    Screen& display(std::ostream &os)
      {
    do_display(os);
    return *this;
 }
    const Screen& display(std::ostream &os) //const
     {
   do_display(os);
   return *this;
 }
private:
     // single function to do the work of displaying a Screen,
     // will be called by the display operations
     void do_display(std::ostream &os) const
      {
    os << contents;
   }
    // as before
private:
    std::string contents;
    index cursor;
    index height, width;
    // other members as before
};

Screen& Screen::set(char c)
{
    contents[cursor] = c;
    return *this;
}

Screen& Screen::move(index r, index c)
{
    index row = r * width; // row location
    cursor = row + c;
    return *this;
}

Screen& Screen::set(index r, index c, char ch)
{
    index row = r * width; // row location
    contents[row + c] = ch;
    return *this;
}

char Screen::get(index r, index c) const
{
    index row = r * width; // row location
    return contents[row + c];
}