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

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://www.*-*-*.com/ .

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

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://www.*-*-*.com/ ).

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{*filter*}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;

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

The perlfaq-workers, a group of volunteers, maintain the perlfaq. They

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

perlfaq.pod.