PHP Parse error: parse error, expecting `','' or `')'' ...what to do?

Answer 1

isset($_SESSION['username']) && ($_SESSION['username'] == $myusername)

Answer 2

I see an error at

isset()

You can either use

isset($_SESSION['username'])

or

if($_SESSION['username'] == $myusername)

Answer 3

You might wanna try to get a value for $_SESSION['username'] outside if statement. Something like this

$_SESSION['username'] = $myusername;

if(isset($_SESSION['username'])){
    header("location:main_login.php");
}