​

var x = 0; // 

var speed = 3; // need to assign variables

function setup() {

  createCanvas(400, 400);

​

}

​

function draw() {

  background(0);

  stroke(180,0,220);

  strokeWeight(5);

  fill(255,0,255,100);

  rect(x, 150, 100,100);

​

  if (x > 300 || x <0) { // conditional stament used here as bouncing rect. you can use width instead of writing the number but here i wanted to make it bounce of screen.

  // x = -3  //this was a part of an error but what it does is it goes back to the starting point every time. check it out.

    speed = speed * -1;

  } 

x = x + speed; // you can see your variables being used.

}

​