#include "library.h"

const double pi = acos(-1.0);

void dc(const double xc,
        const double yc,
        const double alpha,
        const double radius)
{ if (alpha < 2 * pi)
  { const double x = xc + radius * cos(alpha),
                 y = yc + radius * sin(alpha);
    if (alpha == 0.0)
      move_to(x, y);
    else
      draw_to(x, y);
    dc(xc, yc, alpha + 0.01, radius); } }

void draw_circle(const double xc,
                 const double yc,
                 const double r)
{ dc(xc, yc, 0, r); }

void main()
{ make_window(500, 500);
  draw_circle(250, 250, 200); }