checklogin.php

<?php
session_start();
ob_start();
require 'includes/connect.php';

// Define $username and $password
$username=$_POST['username'];
$password=$_POST['password'];

// To protect MySQL injection (more detail about MySQL injection)
$username = stripslashes($username);
$password = stripslashes($password);
$username = mysql_real_escape_string($username);
$password = mysql_real_escape_string($password);
$sql="SELECT * FROM $tbl_name WHERE username='$username' and password='$password'";
$result=mysql_query($sql);

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

// If result matched $myusername and $mypassword, table row must be 1 row
if($count==1){

// Register $username, $password and redirect to file "login_success.php"
$_SESSION['username'] = $username;
$_SESSION['password'] = $password;
}
else {
echo "Wrong Username or Password";
}
ob_end_flush();
?>