Why is $id used in the echo statement twice?

We use $id twice inside the echo because the get_item_html() function requires 2 parameters.

Ill try and work through an example so you can see why we wrote it like this:

Inside index.php the $random variable holds an array of 4 elements, these are random numbers that refer to the keys in our $catalog array. (array_rand only returns the key not the whole array itself - array_rand )

We can do var_dump($random) to see what that looks like:

array(4) { 
[0]=> int(204) 
[1]=> int(301) 
[2]=> int(302) 
[3]=> int(303) } 

We now have an array of 4 items:

$random = [204, 301, 301, 303]

Next we use a foreach loop to iterate over each item in this $random array and assign each item's value to $id. The first time around the loop $id = 204, second time around $id=301 etc.

We then call the get_item_html() function (from data.php) and pass in $id and $catalog[$id] as parameters. The first time around the loop the call to the get_item_html function will look like this:

get_item_html(204, $catalog[204]);

Using the parameters we just passed to get_item_html() we get the following:

    $output = "<li><a href='details.php?id="204"'><img src='"
        . $catalog[204]["img"] . "' alt='"
        . $catalog[204]["title"] . "' />" 
        . "<p>View Details</p>"
        . "</a></li>";

The get_item_html function returns the html that we can then echo out to the screen.

echo get_item_html($id, $catalog[$id]);

I used a bunch of var_dumps in the index.php file to help me understand what was happening at different stages of the code. Here's the code, just uncomment the var_dumps one at a time for easier reading.

<?php 

include("inc/data.php");
include("inc/functions.php");

$pageTitle = "Personal Media Library";
$section = null;

include('inc/header.php'); ?>
        <div class="section catalog random">

            <div class="wrapper">

                <h2>May we suggest something?</h2>

                    <ul class="items">
                        <?php 
                        $random = array_rand($catalog, 4);
            var_dump($random);
                        foreach($random as $id){

                            echo get_item_html($id, $catalog[$id]);
//              var_dump($id);
//              var_dump($catalog[$id]);
                        } 
//              var_dump( $catalog[101]["img"]);


                        ?>          
                    </ul>

            </div>

        </div>
<?php include('inc/footer.php'); ?>

Hope this helps, let me know if you have any questions :)