Hi Karen, looks like thats the question you mailed me for.

Thank you. That helps.

Hey,

if the number of circles changes, you should use an ArrayList instead of an Array. Then you can use remove(). Be aware, that you should iterate over the array/arraylist in reverse order, if you remove items from it. Otherwise you would get errors when trying to access the last element.
Then you loop through all circles and check the distance to every other circle. That is not necessary, only check the distance to those circles that have not been checked before.
Ah, and you don't have to draw the lines when you call noStroke() before, just put the line() inside the if-clause.

1. int maxCircles = 50;
   ArrayList<Circle> circles = new ArrayList<Circle>();
   
   void setup() {
     size(400, 400);
     smooth();
     for (int i = 0; i < maxCircles; i++) circles.add(new Circle(random(width), random(height), random(20, 40)));
   }
   
   void draw() {
     background(255);
     // remove circles, if radius is smaller than 1
     for (int i = circles.size()-1; i >= 0; i--) {
       if (circles.get(i).r < 1) {
         circles.remove(i);
       }
     } 
   
     //update and draw circles
     for (int i = 0; i < circles.size(); i++) {
       Circle curCircle = circles.get(i);
   
       curCircle.update();
       curCircle.display();
   
       stroke(0, 50);
       // check distance to all circles with greater index
       for (int j = i+1; j <circles.size(); j++) {
         Circle compCircle = circles.get(j);
         if (dist(curCircle.x, curCircle.y, compCircle.x, compCircle.y)<40) {
           if (curCircle.r>2 && compCircle.r>2) {
             line(curCircle.x, curCircle.y, compCircle.x, compCircle.y);
           }
         }
       }
     }
     println("circles: "+circles.size());
   }
   
   void mouseMoved() {
   
     for (int i = 0; i < circles.size(); i++) {
       float distance = dist(mouseX, mouseY, circles.get(i).x, circles.get(i).y);
       if (distance<20) {
         circles.get(i).r--;
       }
     }
   }
   
   class Circle {
     float x, y, vx, vy, r;//store position(x,y), velocity(vx,vy) and size
     Circle(float ax, float ay, float ar) {
       x = ax;
       y = ay;
       r = ar;
   
       vx = random(-.1, .1);
       vy = random(-.1, .1);
     }
     void update() {
       x += vx;//update position based on velocity
       y += vy;
       r=constrain(r, 0, 40);
     }
     void display() {
       noStroke();
       fill(0, 50);
       ellipse(x, y, r, r);
     }
   }