在数据处理中经常需要对大量数据进行汇总，将相同关键字记录的某些数据项的值叠加起来，生成一个分类汇总表。

假设某超级市场销售有m种商品（假设商品的编号为1，2，3，┅┅，m），有n台前台收款机（假设收款机的编号为1，2，3，┅┅，n）进行收款，以记录的形式提供给计算机，每个记录表示某台收款机的一种商品一次交易的数量和销售额。记录由4个域组成：收款机编号、商品编号、销售数量、销售金额。构造一个结构体类型，每次销售数据以一个结构体变量保存在一个数据文件中。

-In the data processing often require large amounts of data summary, the values ​ ​ of some of the same key data items recorded together, and generate a subtotal table.

Suppose a supermarket sales have m kinds of goods (assuming the product is numbered 1,2,3, ┅ ┅, m), there are n front desk cash register (assuming cash registers are numbered 1,2,3, ┅ ┅ , n) be receiving, in the form of records provided to the computer, and each record represents the number of sales of a product once a cash register transactions. Recorded by the four domains: the cash register number, product number, sales volume, sales amount. Construct a structure type, each sale to a structure variable data stored in a data file.