private static void Main(string[] args)
{
User user = (User)SysData.Login("admin", "123");
user.DisplayInfo();
SysManager admin = (SysManager)user;
Teacher teacher = new Teacher("李沙沙", "123", "计算机系", 5000);
admin.insertTeacher(ref teacher);
Student student = new Student("张郭郭", "123", "310760", 60);
admin.insertStudent(ref student);
user = (User)SysData.Login("李沙沙", "123");
user.DisplayInfo();
user = (User)SysData.Login("张郭郭", "123");
user.DisplayInfo();
Console.ReadKey();
}