Warning: mysql_numrows(): supplied argument is not a valid MySQL result resource

[Newbi]

Hi i am fairly new to php and am trying to make an application where some1 enters a unique id which brings up a form with data in it retrieved from the database. the user should then be able to
edit the information and submit & the details changed in database, but i keep getting this error which will not even let me view the page. i have really tried to sus it out, please help :-)

$query=" SELECT * FROM contacts WHERE id='$id'";
$result=mysql_query($query);
$num=mysql_numrows($result);        //// it seems to have a prob with this line
mysql_close();

$i=0;
while ($i < $num) {
$first=mysql_result($result,$i,"first");
$last=mysql_result($result,$i,"last");
$phone=mysql_result($result,$i,"phone");
$mobile=mysql_result($result,$i,"mobile");
$fax=mysql_result($result,$i,"fax");
$email=mysql_result($result,$i,"email");
$web=mysql_result($result,$i,"web");
?>
<form action="updated.php" method="post">
<input type="hidden" name="ud_id" value="<? echo $id; ?>">
First Name: <input type="text" name="ud_first" value="<? echo $first; ?>"><br>
Last Name: <input type="text" name="ud_last" value="<? echo $last; ?>"><br>
Phone Number: <input type="text" name="ud_phone" value="<? echo $phone; ?>"><br>
Mobile Number: <input type="text" name="ud_mobile" value="<? echo $mobile; ?>"><br>
Fax Number: <input type="text" name="ud_fax" value="<? echo $fax; ?>"><br>
E-mail Address: <input type="text" name="ud_email" value="<? echo $email; ?>"><br>
Web Address: <input type="text" name="ud_web" value="<? echo $web; ?>"><br>
<input type="Submit" value="Update">
</form>
<?php
++$i;
}
?>

[mrcniceguy]

it should be like this

$num=mysql_num_rows($result);

also whenever open php anywere
it should be

<?php ?>

and not like here

<input type="hidden" name="ud_id" value="<? echo $id; ?>">

[Newbi]

Thank you mrcniceguy, im such a dippy it was only a small thing like that. its working thank you.