Thread: exercise from Stroustrup's text book

This is from chapter 13. Create a class that draws a box with rounded corners. I got the math figured out, but for some reason the lines are not being drawn to the screen. What could be the problem?

Code:

struct Box:Shape {

  Box(Point xxyy, int ww, int hh);

  void Top_segment();
  void Bottom_segment();
  void Left_side_segment();
  void Right_side_segment();

  void draw_lines() const;

  int height() const {
    return h;
  } int width() const {
    return w;
} private:

   Point xy;                    //left most corner

  Lines cornerless_box;         // create a box with no corners using line segments

  int h;                        // height
  int w;                        // width

  double width_tenth;           //10% of the width that will calculate the length to remove from each side to make room for the arcs

};

//----------------------------------------------------------------
//----------------------------------------------------------------
//----------------------------------------------------------------
Box::Box(Point xxyy, int ww, int hh):w(ww), h(hh), xy(xxyy)
{

  width_tenth = (xy.x + w) * 0.10;

  if (h <= 0 || w <= 0)
    error("Bad rectangle: non-positive side");

}

//----------------------------------------------------------------
void Box::Top_segment()
{

  double top_seg_begin_w;       //where the line segment will begin after deducting 10% of w;
  double top_seg_end_w;         //where the line segment will end after deducting 10% of w;

  top_seg_begin_w = xy.x + width_tenth;
  top_seg_end_w = (xy.x + w) - width_tenth;

  double top_seg_y = xy.y;

  cornerless_box.add(Point(top_seg_begin_w, top_seg_y),
                     Point(top_seg_end_w, top_seg_y));
}

//----------------------------------------------------------------
void Box::Bottom_segment()
{

  double bottom_seg_begin_w;
  double bottom_seg_end_w;

  bottom_seg_begin_w = xy.x + width_tenth;
  bottom_seg_end_w = (xy.x + w) - width_tenth;

  double y_bottom = xy.y + h;

  cornerless_box.add(Point(bottom_seg_begin_w, y_bottom),
                     Point(bottom_seg_end_w, y_bottom));
}

//----------------------------------------------------------------
//----------------------------------------------------------------
void Box::Left_side_segment()
{
  double left_seg_begin_h;
  double left_seg_end_h;

  left_seg_begin_h = xy.y + width_tenth;

  left_seg_end_h = (xy.y + h) - width_tenth;

  double x_left = xy.x;

  cornerless_box.add(Point(x_left, left_seg_begin_h),
                     Point(x_left, left_seg_end_h));
}

//----------------------------------------------------------------
void Box::Right_side_segment()
{
  double right_seg_begin_h;
  double right_seg_end_h;

  right_seg_begin_h = xy.y + width_tenth;
  right_seg_end_h = (xy.y + h) - width_tenth;

  double x_right = xy.x + w;

  cornerless_box.add(Point(x_right, right_seg_begin_h),
                     Point(x_right, right_seg_end_h));
}