while ( $number >= 0 )

##</code><code>##

while ($number >= 0)
{
    $total += $number;
    $howmany++;

    if ($howmany == 1)
    {
        $largest  = $number;
        $smallest = $number;
    }
    else
    {
        $largest  = $number if $number > $largest;
        $smallest = $number if $number < $smallest;
    }

    print "Please enter a number or -1 to end: ";
    chomp($number = <>);
}