Re: Simple math failing - PHP Bug?

We have a chapter in the manual about this, http://www.php.net/manual/en/language.types.float.php This is also interesting: http://docs.python.org/tut/node15.html Kind Regards, Aidan "Brian T. Allen" <brian@gzmarketing.com> wrote in message news:4185C110.9050106@gzmarketing.com... > Hi, > > OK, I'm totally stumped by this. This should be the simplest math > imaginable (addition and subtraction), but PHP is coming up with the wrong > answer! > > I've checked on 3 different machines (all linux) running both PHP 4 and > PHP 5. > > Here is the code to duplicate the problem: > > ----------------------------------- > <?php > > $a = 2503.54; > $b = 303.55; > $c = 202.13; > > $total = 0; > $total += $a; > $total += $b; > $total += $c; > > $added_total = $total; > > echo "$a + $b + $c = $total<br>"; > echo "Actual: $total<br><br>"; > > $total -= $a; > $total -= $b; > $total -= $c; > > echo "$added_total - $a - $b - $c = 0<br>"; > echo "Actual: $total<br><br>"; > > ?> > ----------------------------------- > > This ~should~ output this: > > 2503.54 + 303.55 + 202.13 = 3009.22 > Actual: 3009.22 > > 3009.22 - 2503.54 - 303.55 - 202.13 = 0 > Actual: 0 > > But instead it outputs this: > > 2503.54 + 303.55 + 202.13 = 3009.22 > Actual: 3009.22 > > 3009.22 - 2503.54 - 303.55 - 202.13 = 0 > Actual: 2.84217094304E-13 > > > Now I'm the first to admit that 0.000000000000284217094304 and 0 are > really very close, but when you are testing a variable to see if it equals > 0, it is the difference between true and false. > > This seems very, very basic to me, but I can't find the flaw in my code. > > Is this legitimately bad math on the part of PHP? > > Thanks, > Brian