程序代码：

   for (List<Employee> ec = EmployeeCollection; ec != null && ec.Count > 0;) 
    { 
      foreach (Employee e in ec) 
      { 
        s += e.salary; 
      } 
      List<Employee> list = new List<Employee>(); 
      foreach (Employee e in ec) 
      { 
        if (e.EmployeeCollection != null) list.AddRange(e.EmployeeCollection); 
      } 
      ec = list; 
    }