<?php
$link = "r10.net";
echo "<a href=\"$link\">$link</a>";
?>

////

<?php
$link = "r10.net";
?>
<a href="<?php echo $link;?>"><?php echo $link;?></a>

///

<?php
$link = "r10.net";
echo "<a href='$link'>$link</a>";
?>