http://www.perlmonks.org?node_id=1054315


in reply to Printf/Sprintf Behavior Change

What Every Computer Scientist Should Know About Floating-Point Arithmetic

In this case, the code 

printf "%0.018f\n", 0.345;
printf "%0.018f\n", (3.49 / 2) - 1.4;

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outputs (on my computer, it's platform dependent) 
0.344999999999999970
0.345000000000000200

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You are getting different numbers because you are dealing with different numbers. If you need absolute precision, there are ways to handle it, but they are generally not worth the effort it takes to implement them.

#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

In Section Seekers of Perl Wisdom