<?php 
session_start(); 

//This displays your login form 
function index(){ 
echo "<form action='?act=login' method='post'>"  
."Username: <input type='text' name='username' size='30'><br>" 
."Password: <input type='password' name='password' size='30'><br>" 
."<input type='submit' value='Login'>" 
."</form>";  
} 

//This function will find and checks if your data is correct 
function login(){ 

//Collect your info from login form 
$username = $_REQUEST['username']; 
$password = $_REQUEST['password']; 


//Connecting to database 
$connect = mysql_connect("localhost:3306","root","1234"); 
if(!$connect){ 
die(mysql_error()); 
} 

//Selecting database 
$select_db = mysql_select_db("youtube", $connect); 
if(!$select_db){ 
die(mysql_error()); 
} 

//Find if entered data is correct 
$result = mysql_query("SELECT * FROM user WHERE username='$username' AND password='$password'"); 
$row = mysql_fetch_array($result); 
$id = $row['id']; 

$select_user = mysql_query("SELECT * FROM user WHERE id='$id'"); 
$row4 = mysql_fetch_array($select_user); 
$user = $row4['username']; 

if($username != $user){ 
die("Username is wrong!"); 
} 

$pass_check = mysql_query("SELECT * FROM user WHERE username='$username' AND id='$id'"); 
$row3 = mysql_fetch_array($pass_check); 
$email = $row3['email']; 
$select_pass = mysql_query("SELECT * FROM user WHERE username='$username' AND id='$id' AND email='$email'"); 
$row5 = mysql_fetch_array($select_pass); 
$real_password = $row5['password']; 

if($password != $real_password){ 
die("Your password is wrong!"); 
} 

//Now if everything is correct let's finish his/her/its login 

session_register("username", $username); 
session_register("password", $password); 

echo "Welcome, ".$username." please continue on our <a href=index.php>Index</a>"; 

} 
$act = $_REQUEST['act'];
switch($act)
{ 
default:
index(); 
break; 

case "login":
login(); 
break; 
} 
?>

$act = $_REQUEST['act'];
switch($act)
{ 
default:
index(); 
break; 

case "login":
login(); 
break; 
}

if (isset($_REQUEST['act'])) {
    if ($_REQUEST['act'] == 'login') login();
    else index();
    }
else
    index();