Php redirect of vbulletin urls to phpbb forum urls

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PHP

I am trying to redirect some urls that were used under vBulletin but I can't get the PHP code to work
if any number is in the url p value I want it to pass through to the t value - that part works fine,
but when the p value is equal to 724166 then I want the $forum value changed to 2330,
that part does not work.

what I want it to do is:
if the incoming url has p=724166 in it
then I want it to change $forum to 2330 and output t=2330
but that if statement does not work for some reason???

What I have tried:

<?php
if (!empty($_GET['p']))
{
    $forum = (int) $_GET['p'];
    if ($forum = 724166)
    {$forum = 2330}
    header('HTTP/1.1 301 Moved Permanently');
    header('Location: http://hundredbling.net/viewtopic.php?t=' . $forum);
}
?>

<?php
if (!empty($_GET['p']))
{
    $forum = (int) $_GET['p'];
    if ($forum == 724166)
    {$forum = 2330}
    header('HTTP/1.1 301 Moved Permanently');
    header('Location: http://hundredbling.net/viewtopic.php?t=' . $forum);
}
?>

when I try either of these the output is usually the same

http://hundredbling.net/viewtopic.php?t=724166.0

I don't understand why it does not change to t=2330 and I also don't understand why it adds the .0 on the end?