elseif ($var = '0') not working

Good morning. I'm having a problem with elseif.

Im practicing trying to implement a bank system on a game project of mine. If you could help me with this little issue i would appreciate.

Take a peak:

i have this code:

<?php
session_start();
include ('include/dbconnect.php');
$res = mysql_query("SELECT * FROM users WHERE user_id=".$_SESSION['user']);
$userRow = mysql_fetch_array($res);



            $in = $_POST['entrar'];
            $pocketremain = ($userRow['money'] - $in);
            $bankremain = ($userRow['bank'] + $in);

if ($in < $userRow['money']) {
// QUERIES
                mysql_query("UPDATE users SET money ='".$pocketremain."'     WHERE user_id ='".$_SESSION['user']."'");
                mysql_query("UPDATE users SET bank ='".$bankremain."' WHERE     user_id ='".$_SESSION['user']."'");
                $string = "<br><font size='2'><font color='green'>SUCCESS !!    </font><br>You deposited $in$.<br>You now have $bankremain$ in the Bank<br>and     $pocketremain$ in your Pocket.</font>";
}
// FIM DE QUERIES
    elseif ($in <= '0') {
        $string = "<br><font size='2'><font color='red'>FAIL !!</font>     <br>You cant deposit imaginary money!</font>";
    }
    else {
        $string = "<br><font size='2'><font color='red'>FAIL !!</font>     <br>Your values are Wrong!</font>";
    }


?> 

I still can depoisit Zero money in the bank. Elseif should be stating that $string if 0 was set as value. If you could kill this for me i would appreciate, i have been trying to work around this for hours now.

Thank you! Have a nice morning