void setup()
{
  size(200,200);
  smooth();
}

void draw()
{
  background(255);
  stroke(0);
  noFill();
  drawCircle(width/2,height/2,100);
}

void drawCircle(int x, int y, int radius)
{
  // base case
  if (radius <= 2)
  {
    ellipse(x,y,radius,radius);
  }
  // recursive case
  else
  {
    ellipse(x,y,radius,radius);
    drawCircle(x+radius/2,y,radius/2);
    drawCircle(x-radius/2,y,radius/2);
    drawCircle(x,y+radius/2,radius/2);
    drawCircle(x,y-radius/2,radius/2);
  }
  
  
  /* why is the above code equivalent to?
  
  ellipse(x,y,radius,radius);
  if (radius > 2)
  {
    drawCircle(x+radius/2,y,radius/2);
    drawCircle(x-radius/2,y,radius/2);
    drawCircle(x,y+radius/2,radius/2);
    drawCircle(x,y-radius/2,radius/2);
  }
  
  */
  
}