function setup() {
  createCanvas(400, 400);
  background(220);

  // test with different parameters
  head(200, 100, 100);
  head(200, 200, 50);
  head(200, 300, 10);
}

// x, y: the center of the head
// diam: the diameter of the head
function head(x, y, diam) {
  // [Your Code Here]

  fill("rgb(0,255,0)");
  circle(x, y, diam);

  // eyes
  x_factor = diam * 0.15;
  y_factor = diam * 0.1;
  fill("rgb(0,0,0)");
  circle(x - x_factor, y - y_factor, x_factor);
  fill("rgb(0,0,0)");
  circle(x + x_factor, y - y_factor, x_factor);

  // mouth
  noFill();
  arc(x, y + y_factor, x_factor * 2, x_factor * 2, 0, PI);
}