main_login.php

<table width="294" border="0" align="center" cellpadding="0" cellspacing="1" bgcolor="#FFFFFF" bordercolor="#FFFFFF">
<tr>
<form name="form1" method="post" action="index.php?id=checklogin">
<td>
<table width="100%" border="0" cellpadding="3" cellspacing="1" bgcolor="#CCCCCC" bordercolor="#66FF33">
<tr>
<td colspan="3"><center><strong>Geckoville Login</strong></center></td>
</tr>
<tr>
<td width="78"><div align=right>Username: </align></td>
<td width="294"><input name="myusername" type="text" id="myusername"></td>
</tr>
<tr>
<td><div align=right>Password: </align></td>
<td><input name="mypassword" type="password" id="mypassword"></td>
</tr>
<tr>
<td colspan="3"><center><input type="submit" name="Submit" value="Login"></center></td>
</tr>
</table>
</td>
</form>
</tr>
</table>

checklogin.php

<?php
session_start();
require("db.php");
$myusername=$_POST['myusername'];
$mypassword=$_POST['mypassword'];

// 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);
$mypassword = md5($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

if($count==1){
$id = mysql_query("SELECT id FROM $tbl_name WHERE username='$myusername'");
while($row = mysql_fetch_row($id))
{
$_SESSION['id'] = $row[0];
}
// Register $myusername, $mypassword and redirect to file "login_success.php"
session_register("myusername");
session_register("mypassword");
header("location:index.php?id=login_success");
}
else {
echo "Wrong Username or Password";
}
?>

 login_success.php

<?
include('loginonly.php');
if(!session_is_registered(myusername)) {
header("location:index.php?id=main_login");
}
?>

Login Successful!

loginonly.php

<?php
session_start();
if($_SESSION['id'] == 0);
{
header('Location: index.php?id=main_login');
}
?>