Problems with the <?php the_ID(); ?>

Hello!

First of all, I am trying to make a function in .php which checks if there is a image in a folder on the server. If the criterias match, it will load the image. This is used on my front page.

You can see my function here:

<?php
$url = 'https://mydomain.no/wp/';
$filename = 'wp-content/uploads/front/post-';
$filetype = '.jpg';
$end = '" width="500" height="310" /></div>';
$start = '<div class="img-fix"><img src="';
$num = '25-';

for ($i = 1; $i <= 2; $i++) {
       if (file_exists($filename . $num . $i . $filetype)) {
             echo $start . $url . $filename . $num . $i . $filetype . $end;
       } else {
             echo '';
       }
}
?>

Okay, if you guys check the “$num = ’25-‘;” out, I want this to be unique in each post. Therefore, I think I need to use the “the_ID” in this case. Isn’t that correct?

So, If I try to change to this: $num = the_ID();, it will print the post number too early. I will maybe end up with the number before the rest of the code, if you guys understand?

So, is it possible to assign the post id to a variable like I am trying to? And it must be working individual in the loop of the index page.

All help is appreciated!