c++ primer学习指导（13）--1.6书店程序

本节源码位于avg_price.cpp中

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

int main12() 
{
    Sales_item total; // variable to hold data for the next transaction

    // read the first transaction and ensure that there are data to process
    if (std::cin >> total) {
        Sales_item trans; // variable to hold the running sum
        // read and process the remaining transactions
        while (std::cin >> trans) {
            // if we're still processing the same book
            if (total.isbn() == trans.isbn()) 
                total += trans; // update the running total 
            else {              
                // print results for the previous book 
                std::cout << total << std::endl;  
                total = trans;  // total now refers to the next book
            }
        }
        std::cout << total << std::endl; // print the last transaction
    } else {
        // no input! warn the user
        std::cerr << "No data?!" << std::endl;
        return -1;  // indicate failure
    }

    return 0;
}