ConcentricCircles.pde

int diam = 10;
float centX, centY;

void setup() {
  size(400, 400);
  frameRate(24);
  smooth();
  centX = width/2;
  centY = height/2;
  stroke(0);
  strokeWeight(5);
  fill(255,0,0);
  background(255,255,0);
}
      
void draw() {
  if (diam <= 400) {
    background(180);
    strokeWeight(5);
    fill(255, 50);
    ellipse(centX, centY, diam, diam);
    
    strokeWeight(1);
    noFill();
    int innerDiam = diam;
    while(innerDiam > 10) {
      ellipse(centX, centY, innerDiam, innerDiam);
      innerDiam -= 10;
    }
  
    diam += 10;  
  }
}