RE: Methods to format a number

that the number is not rounded but truncated to 0, as the int documentation will tell you.

You can get around the truncation problem fairly easily with:

$string = int( ($number * 100) + 5 ) / 100;
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Update: Well Alright then for the pedantic among us, see below ;-) (no offence meant, please don't take any)

my $dec = 100;  # Change as appropriate to give you the number
                # of decimal places you want

int( ($number * $dec) +
  int($number * $dec) % 2 ? 0.5 * $dec : 0) / $dec
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That should sort out the rounding towards an even number.

Nuance

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RE: RE: Methods to format a number
by Corion (Patriarch) on Jun 02, 2000 at 19:20 UTC

While this method is quite slick, it won't work as expected with numbers that are of the form 0.5, as it will always round up to the next number instead of rounding to the nearest even number (a rule which tries to make sure that most rounding errors cancel each other).

Update: nuance has updated the above post, so this post has become meaningless ;).

Here is an example for a case when always rounding up and using the results in further calculation. Adam calls this "premature rounding", but I think there are valid cases to do this, for example when doing accounting or printing invoices. In this example, using the rounded values in further calculations increases the error introduced by rounding :
Consider (for simplicity) 2.5 * 3.5 :

Method Result Error

exact 8.75 0

round up 12.00 3.25

round to nearest even number 8.00 0.75

In this (extreme) example, the rounding errors don't cancel each other out when always rounding up. There are also cases where rounding up and rounding to the nearest even number give the same rounding error (consider 3.5 * 1.5).

And by the way, I'm not pedantic, I'm just trying to be accurate :)

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RE: RE: RE: Methods to format a number

by Adam (Vicar) on Jun 02, 2000 at 21:07 UTC

Corion's post confused me greatly because I had never heard of rounding to the nearest even... so I cruised out onto the internet and discovered a plethora of sites (mostly in college math departments) that defend it! So I am swayed. I also found an interesting site about significant digits.

So, thank you Corion! You have my vote.

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