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FAQ 4.1 Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

 
 
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      04-17-2011
This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

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4.1: Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

For the long explanation, see David Goldberg's "What Every Computer
Scientist Should Know About Floating-Point Arithmetic"
(http://docs.sun.com/source/806-3568/ncg_goldberg.html).

Internally, your computer represents floating-point numbers in binary.
Digital (as in powers of two) computers cannot store all numbers
exactly. Some real numbers lose precision in the process. This is a
problem with how computers store numbers and affects all computer
languages, not just Perl.

perlnumber shows the gory details of number representations and
conversions.

To limit the number of decimal places in your numbers, you can use the
"printf" or "sprintf" function. See the "Floating Point Arithmetic" for
more details.

printf "%.2f", 10/3;

my $number = sprintf "%.2f", 10/3;



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are not necessarily experts in every domain where Perl might show up,
so please include as much information as possible and relevant in any
corrections. The perlfaq-workers also don't have access to every
operating system or platform, so please include relevant details for
corrections to examples that do not work on particular platforms.
Working code is greatly appreciated.

If you'd like to help maintain the perlfaq, see the details in
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