Comparing Value on Submit Vs Database - php

Question

The "dbcred.php" class
<?php
# pdo_testdb_connect.php - function for connecting to the "test" database
function testdb_connect ()
{
$dbh = new PDO("mysql:host=localhost;dbname=dbname", "root", "");
return ($dbh);
}
?>
PHP
<?php
#connect mysql
require_once "dbcred.php";
$dbh = testdb_connect ();
session_start();
$username = $_POST['regduser'];
$userpass = md5($_POST['regdpass']);
$result = mysql_query("SELECT * FROM Student WHERE regduser= '$username' AND regdpass = '$regdpass'");
if (mysql_num_rows($result)!= 1) { $error = "Login failed";
#include "loginform.php";
} else {
$_SESSION['username'] = "$username";
$_SESSION['ip'] = $_SERVER['REMOTE_ADDR'];
#include "membersection.php";
}
?>
HTML
<form action="inc/check_regUsr.php" method="post" id="userLogon">
<div class="field required">
Username: <input type="text" name="regduser" tabindex="1" /><br />
</div>
<div class="field required">
Password: <input type="text" name="regdpass" tabindex="2" /><br />
</div>
<input type="submit" name="submitUser" />
</form>
When I try to submit valid credentials it says: Warning: mysql_num_rows() expects parameter 1 to be resource, boolean given in on line 12
Why does it not like this and how can I fix it?
Thank you

Answer 1

$result = mysql_query("SELECT * FROM Student WHERE regduser= '$username' AND regdpass = '$regdpass'");
I don't know how your database class is working. So I will write a general mysql connect code.
mysql_connect($host,$username,$password);
mysql_select_db($db);
No you can execute the query.