An example showing how you can use a variable to accomplish what the interior for loop is doing without repeating the two drawing commands.

Unit1Lab2UpdateWithVars.js

  // Column 2. Draws 64 rectangles in descending order of transparency in a second column. 
  var y = 0;
  for (i = 65; i < 128; i += 1) {
    //for (y = 0; y <= 640; y += 10) {
      fill(0, 255, 0, i += 1);
      rect(50, y, 40, 5);
      y += 10;
    }
  }
  // Column 3. Draws 64 rectangles in descending order of transparency in a third column.
  for (i = 128; i < 191; i += 1) {
    for (y = 0; y <= 640; y += 10) {
      fill(0, 255, 0, i += 1);
      rect(100, y, 40, 5);

    }
  }
  // Column 4. Draws 64 rectangles in descending order of transparency in a fourth column.
  for (i = 191; i < 255; i += 1) {
    for (y = 0; y <= 640; y += 10) {
      fill(0, 255, 0, i += 1);
      rect(150, y, 40, 5);
    }
  }