习题7.31 定义Sales_item的读写两个成员函数

#include<string>
using namespace std;
class Sales_item
{
public: 
	double avg_price()
		{
			return	revenue/units_sold;
		}
	bool same_isbn(const Sales_item &rhs)
	{
		return this->isbn == rhs.isbn;
	}
	void getSalesItem()
	{
		cout<<this->isbn<<" "<<units_sold<<" "<<revenue<<endl;
	}
	void setSalesItem(string isbn,unsigned units_sold,double revenue)
	{
		this->isbn = isbn;
		this->units_sold = units_sold;
		this->revenue = revenue;
	}
private:
	string isbn;
	unsigned units_sold;
	double revenue;
};