createCanvas(400, 400);

}

​

//let i = 0;

​

function draw() {

  background(220);

  /*

  ellipse(i, 200, 10, 10);

  ellipse(i + 20, 200, 10, 10);

  ellipse(i + 40, 200, 10, 10);

  ellipse(i + 60, 200, 10, 10);

  */

  // START: i = 0

  // END: i = 400

  // INCREMENT: i + 20

  //    START        END    INCREMENT

  for (let i = 0; i < 400; i = i + 20) {

    if (i % 80 == 0) { // % modulus, give the remainder of a division

      fill(255, 0, 0);

    } else {

      fill(0, 0, 255);

    }

    ellipse(i, 50, 15, 15); // ellipses are horizontal

    ellipse(100, i, 15, 15); // ellipses are vertical

  } // end for loop

}