class SalaryComparator
{
public:
   SalaryComparator(bool a) : ascending(a) {}

   bool operator()(const Employee& a, const Employee& b)
   {
      if (ascending)
         return a.get_salary() < b.get_salary();
      else
         return a.get_salary() > b.get_salary();
   }

private:
   bool ascending;
}