(tye)Re2: Unwanted implicit conversion to float

The cleanest way is of course to keep $val as is and to round it only when printing it.

Perhaps I misunderstand what you mean by "clean", but the safest way to deal with money is to round the internal number any time you print something out¹, and use that rounded number for all future calculations. If you are doing calculations with only whole-cent amounts (such as adding up a bunch of deposits), then you should round after every operation (or at least frequently) to prevent tiny round-off errors from accumulating such that your final total is off by one cent when it is finally rounded.

If you are doing calculations with fractional cents, then you need to define exactly where the rounding occurs (for example, interest is applied one a month and is always rounded at that time).

¹ Update: The reason I say "every time you print something out" is that you (almost always) need to round if the value is being reported to the user. You can (and often should) do internal, intermediate calculations in fractional cents, but whenever you report [or could report] an amount to the user, you need to round your internal representation of that amount the same way you [would] round the amount you [could] report.

- tye (but my friends call me "Tye")

Comment on (tye)Re2: Unwanted implicit conversion to float

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Re: (tye)Re2: Unwanted implicit conversion to float by mirod (Canon) on Mar 12, 2001 at 23:54 UTC
Perhaps I misunderstood what I meant by that! You are right in this context of course. The round-off errors here are totally unwanted and should be fixed as early as possible. So the best solution is to work in cents as merlyn suggests as long as we are performing only additions (the error does not happen) and to use `sprintf` as early as possible and to work with the rounded value when dealing with more elaborate calculations. Keeping the value as-is and rounding only the printed one is only valid in a scientific context, where the real number is too long to be printed but further calculation should be based on it and not on the rounded value.	[reply]

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Re: (tye)Re2: Unwanted implicit conversion to float
by mirod (Canon) on Mar 12, 2001 at 23:54 UTC

Perhaps I misunderstood what I meant by that!

You are right in this context of course. The round-off errors here are totally unwanted and should be fixed as early as possible.

So the best solution is to work in cents as merlyn suggests as long as we are performing only additions (the error does not happen) and to use sprintf as early as possible and to work with the rounded value when dealing with more elaborate calculations.

Keeping the value as-is and rounding only the printed one is only valid in a scientific context, where the real number is too long to be printed but further calculation should be based on it and not on the rounded value.

[reply]