My url does not get the id parameter in the show? id =. Because?

Question: My url does not get the id parameter in mostra?id=.

Code:

<table class="table table-striped table-bordered table-hover">
<?php foreach($produtos as $p): ?>
  <tr>
    <td><?= $p->nome ?></td>
    <td><?= $p->valor ?></td>
    <td><?= $p->descricao ?></td>
    <td><?= $p->quantidade ?></td>
    <td><a href="https://localhost/estoque/public/produtos/mostra?id=<?php 
        $p->id ?>"><span class="glyphicon glyphicon-search"></span></a></td>
  </tr>
<?php endforeach ?>