I'm of the opinion that, as rounding is generally only for the purpose of *displaying* a result, that the rounding operation should be delayed until the last possible moment. Thus, in general, it's better to do all the adding and other stuff and then round just prior to printing.
Look at it this way: rounding throws away information, specifically that embodied in the digits that get rounded off. Computers can generally handle all that information. It's only when they need to show it to *people* that they need to dumb it down ;) Chuck -----Original Message----- From: Dan Sugalski [mailto:[EMAIL PROTECTED] Sent: Monday, October 13, 2003 2:56 PM To: Bill Stephenson Cc: mac osx list Subject: Re: Weird math... On Mon, 13 Oct 2003, Bill Stephenson wrote: > I've got a script that takes numbers similar to those below and then rounds > them and adds them together using code similar to what is below. [snip] > The code above prints this result (system 10.1.5, perl 5.6.0): > > 1.66, 1.75 > > But shouldn't it be: > > 1.66, 1.76 > > or: > > 1.65, 1.75 > > I'm no math wizard, so if someone could please take the time and tell what > I'm missing here I would very much appreciate it! Welcome to the wonderful world of inexact representations. You're getting bitten by some fundamental issues with floating point representations of numbers. Floating point fractions are base 2, so they can't properly represent anything that's not base 2. (And, since our decimal fractions are base 10, that can be a lot of 'em) There's more explanation in the perl faq, along with some workarounds. Dan
