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POHow do I fix this Perl code so that 1.1 + 2.2 == 3.3?
 

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  1. POHow do I fix this Perl code so that 1.1 + 2.2 == 3.3?
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    <p>How do I fix this code so that 1.1 + 2.2 == 3.3? What is actually happening here that's causing this behavior? I'm vaguely familiar with rounding problems and floating point math, but I thought that applied to division and multiplication only and would be visible in the output.</p> <pre><code>[me@unixbox1:~/perltests]&gt; cat testmathsimple.pl #!/usr/bin/perl use strict; use warnings; check_math(1, 2, 3); check_math(1.1, 2.2, 3.3); sub check_math { my $one = shift; my $two = shift; my $three = shift; if ($one + $two == $three) { print "$one + $two == $three\n"; } else { print "$one + $two != $three\n"; } } [me@unixbox1:~/perltests]&gt; perl testmathsimple.pl 1 + 2 == 3 1.1 + 2.2 != 3.3 </code></pre> <p>Edit:</p> <p>Most of the answers thus far are along the lines of "it's a floating point problem, duh" and are providing workarounds for it. I already suspect that to be the problem. How do I demonstrate it? How do I get Perl to output the long form of the variables? Storing the $one + $two computation in a temp variable and printing it doesn't demonstrate the problem.</p> <p>Edit:</p> <p>Using the sprintf technique demonstrated by aschepler, I'm now able to "see" the problem. Further, using bignum, as recommended by mscha and rafl, fixes the problem of the comparison not being equal. However, the sprintf output still indicates that the numbers aren't "correct". That's leaving a modicum of doubt about this solution.</p> <p>Is bignum a good way to resolve this? Are there any possible side effects of bignum that we should look out for when integrating this into a larger, existing, program?</p>
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      1. POHow do I fix this Perl code so that 1.1 + 2.2 == 3.3?
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    1. COAhh, OK. Well, you can do this: print "$one + $two != $three\n"; print ($three - ($one + $two)) . "\n"; and you'll see something like: "1.1 + 2.2 != 3.3\n-4.44089209850063e-16\n". Then you can do some string manipulation to put that together in to one variable.
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    2. COPrint `$one + $two - $three` to demo. `perl -e '$one=1.1;$two=2.2;$three=3.3;print $one+$two-$three' ==> 4.44089209850063e-16` YMMV.
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      1. POHow do I fix this Perl code so that 1.1 + 2.2 == 3.3?
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    3. COIf you're going to `use bignum`, use a method of `Math::BigFloat`, not `sprintf`. For example, `print $num->bstr();`. Passing a number to `sprintf` probably just converts it back to an ordinary floating-point (`double`) number before converting to string.
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      1. POHow do I fix this Perl code so that 1.1 + 2.2 == 3.3?
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