let circley = 100;

​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(100);

  if (keyIsPressed) {

    if (keyCode == RIGHT_ARROW) {

      circlex = circlex + 1;

    }

    if (keyCode == LEFT_ARROW) {

      circlex = circlex - 1;

    }

  }

  circle(circlex, circley, 100);

}