If statement to unable and disable

I want to add an if statement where by if unable it will insect into user profile and get to the input in the code below, Have try the below but when i remove yes and leave it empty it show the empty part, but when i add any text it show the other side

Just help me out with how i can arrange it well And the code to handle it in admin page

<?php if ($yes = $_GET["yes"] == "yes"): ?>


html code to run if condition is empty 

<?php else: ?>

html code to run if condition is yes

<?php endif ?>