E2.h

#ifndef E2_h
#define E2_h

#include <string.h>

using namespace std;

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

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

#endif