2.6 自定义数据结构

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书中页数：P64
代码名称：Sales_data.h 和 Sales_data.cc

#ifndef SALES_DATA_H
#define SALES_DATA_H

#include <string>

struct Sales_data {
	std::string bookNo;
	unsigned units_sold = 0;
	double revenue = 0.0;
};
#endif

#include <iostream>
#include <string>
#include "Sales_data.h"

int main()
{
	Sales_data data1, data2;

	// code to read into data1 and data2
	double price = 0;  // price per book, used to calculate total revenue

	// read the first transactions: ISBN, number of books sold, price per book
	std::cin >> data1.bookNo >> data1.units_sold >> price;
	// calculate total revenue from price and units_sold
	data1.revenue = data1.units_sold * price;

	// read the second transaction
	std::cin >> data2.bookNo >> data2.units_sold >> price;
	data2.revenue = data2.units_sold * price;

	// code to check whether data1 and data2 have the same ISBN
	//        and if so print the sum of data1 and data2
	if (data1.bookNo == data2.bookNo) {
		unsigned totalCnt = data1.units_sold + data2.units_sold;
		double totalRevenue = data1.revenue + data2.revenue;

		// print: ISBN, total sold, total revenue, average price per book
		std::cout << data1.bookNo << " " << totalCnt 
		          << " " << totalRevenue << " ";
		if (totalCnt != 0)
			std::cout << totalRevenue/totalCnt << std::endl;
		else
			std::cout  << "(no sales)" << std::endl;

		return 0;  // indicate success
	} else {  // transactions weren't for the same ISBN
		std::cerr << "Data must refer to the same ISBN" 
		          << std::endl;
		return -1; // indicate failure
	}
}