1.22编写程序，读取多个具有相同 ISBN 的销售记录，输出所有记录的和

#include <iostream>
#include "Sales_item.h"
using namespace std;
int main()
{
        Sales_item item, sum_item;
        cout << "enter some groups of data which ISBN is same." << endl;
        while(cin >> item)
        {
                sum_item += item;
        }
        std::cout << "The data sum is " <<  sum_item << std::endl;
        return 0;
}