C++ primer第五版 7.1.3節練習

定義Sales_data的頭文件

#ifndef CH6_H_INCLUDED
#define CH6_H_INCLUDED
#include <iostream>
#include <string>
using namespace std;

struct Sales_data{
	string isbn() const { return bookNo; }
	Sales_data& Combine(const Sales_data&);
	double avg_price() const;
	string bookNo;
	unsigned units_sold = 0;
	double revenue = 0.0;
};

istream& read(istream &, Sales_data &);
ostream& print(ostream &, Sales_data &);
void add_data(Sales_data &, Sales_data &);

#endif

.cpp文件

#include <iostream>
#include "Ch6.h"

Sales_data& Sales_data::Combine(const Sales_data &rhs)
{
	units_sold += rhs.units_sold;
	revenue += rhs.revenue;
	return *this;
}

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

//輸入的信息包括ISBN，售出總數，售出價格
istream& read(istream &is, Sales_data &item)
{
	double price = 0.0;
	is >> item.bookNo >> item.units_sold >> price;
	item.revenue = price*item.units_sold;
	return is;
}

//輸出信息包括ISBN，售出總數，售出總價，售出均價
ostream& print(ostream &os, Sales_data &item)
{
	os << item.isbn() << " " << item.units_sold << " " << item.revenue << " " << item.avg_price();
	return os;
}

void add_data(Sales_data &litem, Sales_data &ritem)
{
	litem.Combine(ritem);
}

#include <iostream>  
#include <string>
#include <vector>
#include "Ch6.h"
using namespace std;

int main()
{
	cout << "請輸入交易記錄(ISBN，售出總數，售出價格)" << endl;
	Sales_data total;  //首先讀取第一條記錄
	if (read(cin, total))
	{
		Sales_data trans;//讀取第二條記錄
		while (read(cin, trans))
		{
			if (total.isbn() == trans.isbn())
			{
				add_data(total, trans);
			}
			else
			{
				//輸出舊書號的記錄
				print(cout, total)<<endl;
				total = trans;//類的拷貝實際上是拷貝數據成員
			}
		}
		print(cout, total) << endl;//輸出最後一條記錄
	}
	else
		cerr << "沒有交易記錄" << endl;

	system("pause");
	return 0;
}