php - How do I add an if / else? -

i using following code pass variable. if variable = a, nothing.

i want check if variable = a, nothing, if b, nothing, else something

<?     if($_get['pageid'] == 'a'){     } else {     include('header_image.php');     }    ?>

above code have working correctly 1 vartiable.

how add if / else?

if($_get['pageid'] != 'a' && $_get['pageid'] != 'b'){ //do smth }

Macro