C++ | 类

Sales_data类

#ifndef SALES_DATA_H
#define SALES_DATA_H
#include<iostream>
#include<string>
using namespace std;

class Sales_data
{
    friend istream& operator >> (istream &in, Sales_data&);
    friend ostream& operator << (ostream &os, Sales_data&);
    friend bool operator == (const Sales_data&, const Sales_data&);
public:
    Sales_data() = default;
    Sales_data(const string &book): bookNo(book) {}
    Sales_data(const string  &book, const unsigned num, const double sellp, const double salep, const double disp):
        bookNo(book), units_sold(num), sellingprice(sellp), discount(disp) {}
    Sales_data(istream &is) { is >> bookNo }
public:
    Sales_data& operator+=(const Sales_data&);
    string isbn() const { return bookNo; }
private:
    string bookNo;         //书籍编号
    double units_sold = 0;  //销售量
    double sellingprice = 0.0; //原始价格
    double saleprice = 0.0;   //实售价格
    double discount = 0.0; //折扣
};

bool operator== (const Sales_data &lhs, const Sales_data &rhs)
{
    return lhs.isbn() == rhs.isbn() &&
        lhs.units_sold == rhs.units_sold &&
        lhs.sellingprice == rhs.sellingprice &&
        lhs.saleprice == rhs.saleprice;
}

Sales_data& Sales_data::operator += (const Sales_data &rhs)
{
    units_sold += rhs.units_sold;
    saleprice = (rhs.saleprice * rhs.units_sold + saleprice * units_sold) / (rhs.units_sold + units_sold);
    if (sellingprice != 0)
        discount = saleprice / sellingprice;
    return *this;
}

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

istream& operator >> (istream &in, Sales_data& s)
{
    in >> s.bookNo >> s.units_sold >> s.sellingprice >> s.saleprice;
    if (in && s.sellingprice != 0)
        s.discount = s.saleprice / s.sellingprice;
    else
        s = Sales_data();
    return in;
}

ostream& operator << (ostream &os, const Sales_data &s)
{
    os << s.isbn() << " " << s.units_sold << " "
        << s.sellingprice << " " << s.saleprice << " " << s.discount;
    return os;
}
#endif