echo" //i need this echo;
<form class='form' action='zoom.php?img=<?php echo intval($_GET['img']);?>' method='post'> //i dont need echo in here
";

i also tired 
action='zoom.php?img= intval($_GET['img'])'
action='zoom.php?img=$_GET['img'])'

but no luck 

it give me syntar error every time

$img = intval($_GET['img']);
echo "<form class='form' action='zoom.php?img=$img' method='post'>";