/*
  Sketch that uses conditional to determine whether a mouse press
  lies within a circle. If so, the circle is recolored. Otherwise,
  the mouse press is ignored.
  
  Author: Michael Goldwasser
*/
float cx, cy, r;    // parameters for circle center (x,y) and radius

void setup() {
  size(500, 400);
  cx = 0.5*width;
  cy = 0.5*height;
  r = 0.25*min(width,height);
  fill(random(255), random(255), random(255));
  ellipse(cx, cy, 2*r, 2*r);
}

void draw() {
  // nothing to do here (but function must be given)
}

void mousePressed() {
  // compute square of distance from mouse press to circle center
  if (dist(mouseX, mouseY, cx, cy) <= r) {
    // click is within circle
    fill(random(255), random(255), random(255));
    ellipse(cx, cy, 2*r, 2*r);
  }
}