php in pages does not accept variables from outside the post

Hello everyone,
I use the php-exec plugin to run php inside pages and posts.

I have some code inside my custom theme in header.php

<?php
...
...
$flag = 1;
?>

Inside a page, using the HTML editor, I insert something like this:

<?php if ($flag == 1){
echo 'It works';
}
else{
echo 'No, it does not';
}
?>

After I save my page and go to the site to see the results, it reads “No, it does not”, which is wrong because $flag = 1 in the header!

That means that the php code inside the post can’t interact with the php code outside the post, in this example, in the header.php!

Any ideas? I tried global $flag; in the header.php but still no luck.

Thanks in advance!