[Newbies] How to round a float?
Ben Coman
btc at openInWorld.com
Wed Feb 4 14:57:51 UTC 2015
On Wed, Feb 4, 2015 at 7:22 PM, Chuck Hipschman <ckhipschman at gmail.com>
wrote:
> 7 / 8.0 roundTo 0.01 = 0.88 Aha! Thanks!
>
> But:
>
> 100 * (1.05 raisedTo: 10) roundTo: 0.01 162.89000000000001
>
> "162.88946267774418" "unrounded"
> 100 * (1.05 raisedTo: 15) roundTo: 0.01 207.89000000000001
>
> "207.8928179411367" "unrounded"
> Bug, or me again :-)
>
>
If you debug into #roundTo: you'll see its implementation is simple
arithmetic, subject to the vagaries of float resolution.
Float(Number)>>roundTo:
^(self / quantum) rounded * quantum
Now are you wanting something nicely formatted for display, or are you
rounding for some mathematic purpose? Perhaps instead you are wanting...
100 * (1.05 raisedTo: 10) printShowingDecimalPlaces: 2 " --> 162.89 "
0.105 printShowingDecimalPlaces: 2 " --> 0.10 "
0.115 printShowingDecimalPlaces: 2 " --> 0.12 "
btw, I only found these today, looking in the printing protocol of Number
and Float.
cheers -ben
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