dev 用不了 ，vs也有点问题 还是vscode好用，简洁又方便
创建一个文件夹，添加头文件和cpp （头文件名字一定要对）
书上的例题
练习1.20
在网站http://www.informit.com/title/032174113上，第1章的代码目录包含了头文件 Sales_item.h。将它拷贝到你自己的工作目录中，并编写一个程序，读取一组书籍销售记录，将每条记录打印到标准输出上。
下载这个 然后解压 找到 这个头文件
或者直接 复制我的内容加到那个头文件里面
#ifndef SALESITEM_H
#define SALESITEM_H
#include <iostream>
#include <string>
class Sales_item {
friend std::istream& operator>>(std::istream&, Sales_item&);
friend std::ostream& operator<<(std::ostream&, const Sales_item&);
friend bool operator<(const Sales_item&, const Sales_item&);
friend bool
operator==(const Sales_item&, const Sales_item&);
public:
#if defined(IN_CLASS_INITS) && defined(DEFAULT_FCNS)
Sales_item() = default;
#else
Sales_item() : units_sold(0), revenue(0.0) {
}
#endif
Sales_item(const std::string &book) :
bookNo(book), units_sold(0), revenue(0.0) {
}
Sales_item(std::istream &is) {
is >> *this; }
public:
Sales_item& operator+=(const Sales_item&);
std::string isbn() const {
return bookNo; }
double avg_price() const;
private:
std::string bookNo;
#ifdef IN_CLASS_INITS
unsigned units_sold = 0;
double revenue = 0.0;
#else
unsigned units_sold;
double revenue;
#endif
};
inline
bool compareIsbn(const Sales_item &lhs, const Sales_item &rhs)
{
return lhs.isbn() == rhs.isbn();
}
Sales_item operator+(const Sales_item&, const Sales_item&);
inline bool
operator==(const Sales_item &lhs, const Sales_item &rhs)
{
return lhs.units_sold == rhs.units_sold &&
lhs.revenue == rhs.revenue &&
lhs.isbn() == rhs.isbn();
}
inline bool
operator!=(const Sales_item &lhs, const Sales_item &rhs)
{
return !(lhs == rhs);
}
Sales_item& Sales_item::operator+=(const Sales_item& rhs)
{
units_sold += rhs.units_sold;
revenue += rhs.revenue;
return *this;
}
Sales_item
operator+(const Sales_item& lhs, const Sales_item& rhs)
{
Sales_item ret(lhs);
ret += rhs;
return ret;
}
std::istream&
operator>>(std::istream& in, Sales_item& s)
{
double price;
in >> s.bookNo >> s.units_sold >> price;
if (in)
s.revenue = s.units_sold * price;
else
s = Sales_item();
return in;
}
std::ostream&
operator<<(std::ostream& out, const Sales_item& s)
{
out << s.isbn() << " " << s.units_sold << " "
<< s.revenue << " " << s.avg_price();
return out;
}
double Sales_item::avg_price() const
{
if (units_sold)
return revenue / units_sold;
else
return 0;
}
#endif
这样不用管的，编译保存就行
main.cpp
#include <iostream>
#include "Sales_item.h"
int main()
{
Sales_item book;
std::cout << "请输入销售记录:"
<< std::endl;
while (std::cin >> book) {
std::cout << "ISBN、售出本数和平均售价为 "
<< book << std::endl;
}
return 0;
}
如果输入：0-201-70353-X 4 24.99
则输出为：0-201-70353-X 4 99.96 24.99
完成！！