初识C++的类

//Sales_item.h
#ifndef SALESITEM_H
#define SALESITEM_H
#include <iostream>
#include<string>
class Sales_item
{
public:
	std::istream &input(std::istream & in);
	std::ostream & output(std::ostream & out)const;
	double avg_price() const;
	bool same_isbn(Sales_item& rhs)const;
	Sales_item add(Sales_item& other);
	Sales_item::Sales_item() :unit_sale(0), revenue(0){}

private:
	std::string isbn;//isbn号
	int unit_sale;//数量
	double revenue;//总价
};

#endif

//Sales_item.cpp
#include "Sales_item.h"
std::istream& Sales_item::input(std::istream & in){
	double price;
	in >> isbn >> unit_sale >> price;
	if (in)
		revenue = unit_sale*price;
	else
	{
		unit_sale = 0;
		revenue = 0.0;
	}
	return in;
}
std::ostream& Sales_item::output(std::ostream & out)const{
	out << isbn << "\t" << unit_sale << "\t"
		<< revenue << "\t" << avg_price();
	return out;
}

double Sales_item::avg_price() const{
	if (unit_sale)
		return revenue / unit_sale;
	else
		return 0.0;
}
bool Sales_item::same_isbn(Sales_item& rhs)const{
	return isbn == rhs.isbn;
}
Sales_item Sales_item::add(Sales_item& other){
		unit_sale += other.unit_sale;
		revenue += other.revenue;
		return *this;
}

　　

//main.cpp
#include <iostream>
//#include <string>
//#include <vector>
//#include <cctype>
//#include <cstring>
//#include <bitset>
#include "Sales_item.h"

using namespace std;

int main(int argc, char **argv)
{
	Sales_item total, trans;
	cout << "Enter some transaction (ctrl + z to end)" << endl;
	if (total.input(cin)){//读入第一个交易
		while (trans.input(cin))
		{
			if (total.same_isbn(trans))
				total.add(trans);
			else
			{
				total.output(cout);
				total = trans;
			}
		}
		//输出最后一个交易
		total.output(cout) << endl;
	}
	else
	{
		cout << "No data!" << endl;
		return -1;
	}

	cout << endl;
	system("pause");
	return 0;
}