PHP conditional processing required to display rotating banners continuously

Question

I'm trying to do something a little different with a banner rotator.

Below is the script I am using to read two text files (stored on my root directory with .db extensions) to rotate banners on a website. One file holds a counter (FileDB), the other holds the HTML banner code (URLDB).

The URLDB file currently holds six lines of HTML code to display hyperlinked banners.

The following script builds an array and rotates these banners sequentially on the refresh of the page counting from 0 - 5, and it does this perfectly:

<?php
define('FILEDB', '/WORKING DIRECTORY/count.db');
define('URLDB', '/WORKING DIRECTORY/url.db');

function readURLS()
{
  $fo = fopen(URLDB, 'r');

  if( null == $fo )
    return false;

  $retval = array();
  while (($line = fgets($fo)) !== false)
  {
    $retval[] = $line;
  }

  return $retval;
}

$list = readURLS();

if( false === $list )
{
  echo "No URLs available";
}
else
{
  $fo = fopen(FILEDB, 'a+');

  $count = (fread($fo, filesize(FILEDB)) + 1) % count($list);

  ftruncate($fo, 0);
  fwrite($fo, "{$count}");
  fclose($fo);

  echo $list[$count];
}

?>

On the webpage that I want to display the banners there are eight placeholders. However I only have six banners.

Here is the PHP code in each of the placeholders:

Placeholder 1: <?php echo $list[$count];?>
Placeholder 2: <?php echo $list[$count +1];?>
Placeholder 3: <?php echo $list[$count +2];?>
Placeholder 4: <?php echo $list[$count +3];?>
Placeholder 5: <?php echo $list[$count +4];?>
Placeholder 6: <?php echo $list[$count +5];?>
Placeholder 7: <?php echo $list[$count +6];?>
Placeholder 8: <?php echo $list[$count +7];?>

With the count at 0 the 6 banners are displayed in placeholders 1 - 6 and placeholders 7 and 8 are blank.

With every refresh the counter is increase by one, showing each banner in the first placed holder and pulling the other banners through each placeholder from 5 through to 0, but leaving previously populated placeholders blank until the sixth banner is in placeholder one. Then on the next refresh banners 1 - 6 are once again shown.

This occurs because I've hardcoded the values in each placeholder and I am obviously attempting to reference an entry in the file that is out of the bounds of the array built by the above script.

You can see a working example here.

What I am trying to achieve is display all banners in the URLDB such that when the last entry is shown, the first entry is displayed in the next placeholder (which in this case is placeholder 7) and the 2nd entry is show in in placeholder 8.

The idea is that the banners move continuously through each of the placeholders like the carriages of a train with each page refresh and increment of the counter - one following the other.

So, now you have the background, on to my question.

Is there a way I can amend the script to store in a PHP variable the maximum number of entries in the URLDB file/array and subsequently add conditional processing in the placeholders to check when the counter reaches this maximum value, and reference the next valid value in the array (i.e. 0) such that the banners restart again in the surplus placeholders - so here are no blank or empty placeholders shown?

I imagine this might seem like a strange request. But of course I would appreciate any advice on how to achieve my goal based on where things are currently.

Answer 1

Once you use a loop things become a bit easier to manipulate. Hopefully the following solves your problem.

$numOfBanners    = count($list);
$numOfPlacements = 8;
for ($i=0; $i < $numOfPlacements; $i++) {
  // use the modulus operator to come back around
  $bannerID = $i % $numOfBanners; 
  echo $list[$bannerID];
}

More info on the modulus operator can be found here.