请基于下面这个名称空间编写一个由3个文件组成的程序： na

namespace SALES
{
          const int QUARTERS = 4；
          struct Sales
          {
                double sales[QUARTERS];
                double average;
                double max;
                double min;
           };
           // copies the lesser of 4 or n items from the array ar
           // to the sales member of s and computes and stores the
           // average, maximum, and minmum values of the entered items;
           // remaining elements of sales, if any, set to 0
           void setSales(Sales & s, const double ar[], int n);
           // gathers sales for 4 quarters interactively, stores them
           // in the sales member of a and computes and stores the
           // average, maximum, and minimum values
           void setSales[Sales & s];
           // display all information in structure s
           void showSales(const Sales & s);
}