you cant use <?php
in side <?php
try the following code:
echo "<a href=\"cust_room/assign_room.php?cust_id={$row_customer['cust_id']}\">Assign Room</a>";
instead of:
echo "<a href=\"https://stackoverflow.com/questions/35861929/cust_room/assign_room.php?cust_id=<?php echo $row_customer["cust_id']; ?>\">Assign Room</a>";