How to redirect a php page with different

Question

I don't have so much knowledge of programming, so I want some help. I want to redirect 301 a url /viewforum.php?f=19 to another page. So want to put in viewform.php to do so. I using the following code

<?php
header("HTTP/1.1 301 Moved Permanently");
header("Location: http://www.example.com/");
exit();
?>

But it redirecting everything within /viewform.php but I only want to redirect /viewform.php?f=19

Answer 1

<?php
        if($_GET['f']==19)
        {    
            //header("HTTP/1.1 301 Moved Permanently"); no need
            header("Location: http://www.example.com/");
            exit();
        }
?>

Hope it will help