text: #include "exercise_04/exercise_4.h"
  
  
  void exercise_4()
  {
      Rectangle r(Point(50,50), 300, 200);
      Simple_window win(Point(50,50), 500, 500, "Exercise 4");
      Vector_ref<Mark> marks;
      marks.push_back(new Mark(*n(r), 'x'));
      marks.push_back(new Mark(*ne(r), 'x'));
      marks.push_back(new Mark(*e(r), 'x'));
      marks.push_back(new Mark(*se(r), 'x'));
      marks.push_back(new Mark(*s(r), 'x'));
      marks.push_back(new Mark(*sw(r), 'x'));
      marks.push_back(new Mark(*w(r), 'x'));
      marks.push_back(new Mark(*nw(r), 'x'));
      marks.push_back(new Mark(*center(r), 'x'));
      for (int i = 0; i < marks.size() ; i++)
      {
          marks[i].set_color(Color::red);
          win.attach(marks[i]);
      }
      win.wait_for_button();
  }
  
  
  int main()
  {
      try 
      {
          exercise_4();
      }
      catch (...)
      {
          cout << "MAJOR ERROR!";
          return -1;
      }
      return 0;
  }