Alpha diamond

gistfile1.phtml

<?php
if ($_SERVER['REQUEST_METHOD'] == 'POST') {
  $size = ord($_POST['size']) - 64;
  $diamond = [];
  
  for ($i = 0; $i < $size; $i++) {
    $row = str_pad(str_pad(chr(65 + $i), $size - $i, ' ', STR_PAD_LEFT), $size);
    $row .= strrev(substr($row, 0, $size - 1));
    
    array_splice($diamond, $i, 0, $row);
    
    if ($i < $size - 1) {
    	array_splice($diamond, $i, 0, $row);
    }
  }
} else {
  $diamond = null;
} 
?>

<form method="POST">
  <input name="size" value="A">
  <input type="submit" value="Submit">
</form>

<?php if ($diamond !== null): ?>
<pre>
  <?php foreach ($diamond as $row): ?>
  <?php echo $row ?><br>
  <?php endforeach; ?>
</pre>
<?php endif; ?>