Re: Rounding off numbers
Re: Rounding off numbers
- Subject: Re: Rounding off numbers
- From: James Bucanek <email@hidden>
- Date: Sat, 10 Jun 2006 09:56:01 -0700
Johan Augustsson wrote on Saturday, June 10, 2006:
>Hi!
>
>I have a problem when I round of numbers. My first question is if
>there aren't any smother way to round off an NSNumber. I do it like
>this:
>
>myNbr is an NSNumber.
>NSNumber *myRoundedNbr=[NSNumber numberWithDouble:[[NSString
>stringWithFormat:@"%.2f", [myNbr floatValue]] doubleValue]];
>
>
>
>The bigger problem is that it doesn't round of correctly. Some tests
>show this:
>
>Nbr Rounded
>2.265 => 2.27 OK
>2.865 => 2.87 OK
>2.965 => 2.96 WRONG
From the man page for printf regarding %e and %f:
Since the floating point numbers are translated from ASCII to floating-
point and then back again, floating-point precision may be lost.
If you want a specific rounding, using the math functions to get the exactly that you want (i.e. don't rely on %f to do it for you -- and not to mention that it will be at least an order of magnitude more efficient):
static NSNumber* sNumberRoundedToHundreds( float number )
{
return ([NSNumber numberWithFloat:roundf(number*100)/100]);
}
--
James Bucanek
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