ex3_1b.cpp

#include <iostream>
#include <string>
#include "../ch02/Sales_data.h"

using std::cin;
using std::cout;
using std::endl;
using std::cerr;

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 
  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
  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
    cout << data1.bookNo << " " << totalCnt 
         << " " << totalRevenue << " ";
    if (totalCnt != 0)
      cout << totalRevenue/totalCnt << endl;
    else
      cout  << "(no sales)" << endl;

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