PHP & MySQL: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given

I'm trying to Integrate HTML Purifier http://htmlpurifier.org/ to filter my user submitted data but I get the following error below. And I was wondering how can I fix this problem?

I get the following error.

on line 22: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given 

line 22 is.

if (mysqli_num_rows($dbc) == 0) {

Here is the php code.

if (isset($_POST['submitted'])) { // Handle the form.

	require_once '../../htmlpurifier/library/HTMLPurifier.auto.php';

	$config = HTMLPurifier_Config::createDefault();
	$config->set('Core.Encoding', 'UTF-8'); // replace with your encoding
	$config->set('HTML.Doctype', 'XHTML 1.0 Strict'); // replace with your doctype
	$purifier = new HTMLPurifier($config);


	$mysqli = mysqli_connect("localhost", "root", "", "sitename");
	$dbc = mysqli_query($mysqli,"SELECT users.*, profile.*
								 FROM users 
								 INNER JOIN contact_info ON contact_info.user_id = users.user_id 
								 WHERE users.user_id=3");

	$about_me = mysqli_real_escape_string($mysqli, $purifier->purify($_POST['about_me']));
	$interests = mysqli_real_escape_string($mysqli, $purifier->purify($_POST['interests']));



if (mysqli_num_rows($dbc) == 0) {
		$mysqli = mysqli_connect("localhost", "root", "", "sitename");
		$dbc = mysqli_query($mysqli,"INSERT INTO profile (user_id, about_me, interests) 
									 VALUES ('$user_id', '$about_me', '$interests')");
}



if ($dbc == TRUE) {
		$dbc = mysqli_query($mysqli,"UPDATE profile 
									 SET about_me = '$about_me', interests = '$interests' 
									 WHERE user_id = '$user_id'");

		echo '<p class="changes-saved">Your changes have been saved!</p>';
}


if (!$dbc) {
		// There was an error...do something about it here...
		print mysqli_error($mysqli);
		return;
}

}

$dbc is returning false. Your query has an error in it:

SELECT users.*, profile.* --You do not join with profile anywhere.
                                 FROM users 
                                 INNER JOIN contact_info 
                                 ON contact_info.user_id = users.user_id 
                                 WHERE users.user_id=3");

The fix for this in general has been described by Raveren.

The query either returned no rows or is erroneus, thus FALSE is returned. Change it to

if (!$dbc || mysqli_num_rows($dbc) == 0)

mysqli_num_rows:

> Return Values > > Returns TRUE on success or FALSE on > failure. For SELECT, SHOW, DESCRIBE or > EXPLAIN mysqli_query() will return a > result object.