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

Discussion in 'Perl Misc' started by PerlFAQ Server, Apr 17, 2011.

  1. 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 .

    --------------------------------------------------------------------

    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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    PerlFAQ Server, Apr 17, 2011
    #1
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