Maps in P5

/** Draw a bunch of rectangles that are
  * different sizes (use a for loop)
  * and different color.
  */
var r, g, b;  //Color variables
var num, w, h;

function setup() {
  createCanvas(700, 500);
  r = 0;
  g = 0;
  b = 0;
  num = 60;
  w = 0;
  h = 0;
  //noStroke();
}

function draw() {
  background(220);
  fill(255);
  for(var i = num; i > 0; i--){
    //r = 5*i;
    r = map(i, 0, num, 0, 255);
    h = map(i, 0, num, 0, height);
    w = map(i, 0, num, 0, width);
    fill(r, 0, 0);
    rect(0, 0,w, h);
  }

}