void draw_canvas_mode(int mode, int color, int y, int h);
void update_canvas();
int keypress_event();
int resize_event(int w, int h);
void get_point_extents(HistogramPoint *current,
void draw_canvas_mode(int mode, int color, int y, int h);
void update_canvas();
int keypress_event();
int resize_event(int w, int h);
void get_point_extents(HistogramPoint *current,