Check login details

<?php
session_start();
/**
 * These are the database login details
 */
 $host="localhost"; // Host name
$username="root"; // Mysql username
$password=""; // Mysql password
$db_name="loginregister"; // Database name
$tbl_name="userdata"; // Table name

// Connect to server and select databse.
mysql_connect("$host", "$username", "$password")or die("cannot connect");
mysql_select_db("$db_name")or die("cannot select DB");

// username and password sent from form
$myusername=$_POST['myusername'];
$mypassword=$_POST['mypassword'];

echo $myusername ."<br>";
echo $mypassword."<br>";

// To protect MySQL injection (more detail about MySQL injection)
$myusername = stripslashes($myusername);
$mypassword = stripslashes($mypassword);
$myusername = mysql_real_escape_string($myusername);
$mypassword = mysql_real_escape_string($mypassword);

$sql="SELECT * FROM $tbl_name WHERE username='$myusername' and password='$mypassword'";
$result=mysql_query($sql);

// Mysql_num_row is counting table row
$count=mysql_num_rows($result);

// If result matched $myusername and $mypassword, table row must be 1 row


$data_row=mysql_fetch_array($result);;

if($count==1){
$user_id=$data_row["id"];
// Register $myusername, $mypassword and redirect to file "login_success.php"
$_SESSION["myusername"]=$myusername;
$_SESSION["user_id"]=$user_id;

//session_register("mypassword");
//session_register("id");
header("location:homepage.php");
}
else {
echo "Wrong Username or Password";
}
?>