Flexibility within 'Print/Echo' - php

Question

I made this code:
<?php if($this->session->userdata('login_user_id'));
$a = $this->session->userdata('login_user_id');
$b = mysql_query("SELECT * FROM user WHERE id='$a' AND specialrank='1'")
or die(mysql_error());
while($c = mysql_fetch_array( $b ))
{
Print $c['username'];
}
?>
basically it creates a session for the logged in user.
I want to be able to show more in the print section though, some advanced php code and html form. Is there a way I can do this by reworking the code? It seems I'm limited with regards to which characters I can use within the print statement.
Basically, I want to display a form to specific users and not others.
I have tried closing the <?php ?> tags after every line to see if that works but it throws up errors of unexpected and expected's etc.
EDIT:
this is the segment of code I want to show:
<?php // update
if(isset($_POST['update']))
{
$id = $_POST['id'];
$emp_salary = $_POST['emp_salary'];
$sql = "UPDATE pins SET is_private = $emp_salary WHERE id = $pinDetails->id";
mysql_select_db('test_db');$retval = mysql_query( $sql );if(! $retval )
{ die('Could not change: ' . mysql_error());
}
echo "Post is now private<br><br>";
}
?>
<form method="post" action="<?php $_PHP_SELF ?>">
<table width="400" border="0" cellspacing="1" cellpadding="2">
<tr>
<td>Private
<input name="emp_salary" type="text" id="emp_salary" value="1">
<input name="id" type="hidden" id="id">
<input name="update" type="submit" id="update" value="Change">
</td>
</tr>
</table>
</form>
As you can see, simply putting that within the print throws up so many errors.