//LOGGING IN-USER\\
if(isset($_POST['action']) == "login"){
     //Defining special variables (username and password)
     $username = strtolower(mysql_real_escape_string($_POST['username']));
     $password = mysql_real_escape_string($_POST['password']);


     //Getting Information
     $sql = mysql_query("SELECT * FROM `user` WHERE `Id`='$username'") or die(mysql_error());
     $sqlly = mysql_fetch_assoc($sql);
     $dbusername = strtolower($sqlly['Id']);
     $dbpassword = $sqlly['Password'];
     //Starting Verification Process
     if(!$password || !$username){die("<script>alert('Fill in all fields'); history.back();</script>");}

     if(!eregi("^[a-zA-Z0-9]*$", mysql_real_escape_string($_POST['username']))){
     die("<script>alert('Username must be alpha-numeric'); history.back();</script>");
     }

     if($username != $dbusername){die("<script>alert('Username not found'); history.back();</script>");}
    if($password != $dbpassword){die("<script>alert('Incorrect password'); history.back();</script>");}

     if (strlen($password)>16 || strlen($password)<4){die("<script>alert('Password must be between 4~16 characters'); history.back();</script>");}

     if (strlen($username)>16 || strlen($username)<4){die("<script>alert('Username must be between 4~16 characters'); history.back();</script>");}
    session_start();
     $_SESSION['user']=$username;
     }