Question

I’ve notice that when one of the two conditions in a php if statement is not true. You get an undefined index notice for the statement that is not true. And the result in my case is a distorted web page.
For example, this code:

<?php
session_start();

if (!isset($_SESSION['loginAdmin']) && ($_SESSION['loginAdmin'] != '')) {
    header ("Location: loginam.php");
} else {
    include('head2.php');
}



if (!isset($_SESSION['login']) && ($_SESSION['login'] != '')) {
    header ("Location: login.php");
} else {
    include('head3.php'); 
}
?>    

If one of the if statements is not true. The one that is not true will give you a notice that it is undefined.
In my case it says that the session ‘login’ is not defined. If session ‘LoginAdmin’ is used. What can you recommend that I would do in order to avoid these undefined index notice.

EDIT
This is where I check if the entered information is correct, for those who are asking. It always redirects to the login page even if the login information is correct:

$uname = mysql_real_escape_string($_POST['ausername']);
        $pword = mysql_real_escape_string($_POST['apassword']);
        $idnam= mysql_real_escape_string($_POST['aydi']);

        $SQL = "SELECT * FROM admin WHERE  ID= '$idnam' AND admin = '$uname' AND admin_password = '$pword'";
        $result = mysql_query($SQL);
        $num_rows = mysql_num_rows($result);



        if ($result) {
            if ($num_rows > 0) {
                session_start();
                $_SESSION['loginAdmin'] = "1";
                header ("Location: ampage.php");
            }
            else {
                session_start();
                $_SESSION['loginAdmin'] = "";
                header ("Location: loginam.php");
            }   
        }
        else {
            $errorMessage = "Error logging on, please try again.";
        }

Answer 1

Your condition is wrong, it should be:

if (!isset($_SESSION['loginAdmin']) || ($_SESSION['loginAdmin'] == '')) {
    header ("Location: loginam.php");
} else {
    include('head2.php');
}

And:

if (!isset($_SESSION['login']) || ($_SESSION['login'] == '')) {
    header ("Location: login.php");
} else {
    include('head3.php'); 
}

replaced && with || and != with ==

You get an undefined index notice for
the statement that is not true.

That’s not the case, you get notice messages when you have some variables undefined. You can avoid this be using suppression operator @ but it is not a good idea to use that because it slows down performance.

Also you can hide notice messages by putting this on top of your script:

error_reporting(E_ALL ^ E_NOTICE);

But again while on development, you must be aware of all errors and notices so this is not a good idea again unless you are sure what you are doing.