The problem is that 0.001 cannot be exactly stored as a floating-point number, just as you cannot store 1/3 exactly as a decimal number. See What Every Computer Scientist Should Know About Floating-Point Arithmetic for details, or search for floating point here on perlmonks.

A way around is to start $a as 22400, add 1 to it at each iteration, and remember to divide by 1000 in the end before using the result (or never divide by 1000, but use the result in a way that accounts for the additional factor)

Note that Perl 6 solves the problem by storing 0.001 as a rational number by default.

use v6;
my $a = 22.400;

for (1..43)
{
$a = $a + 0.001;
}
print "$a\n";
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produces 22.443 as output with Rakudo and Niecza.

printf "%.3f\n", $a;
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What are you actually trying to do? What precision (how many digits) do you really need? Moritz provided a good solution (work with integer values then scale as the last step) - what is wrong with that solution?

As an exercise try writing 1/3 as a decimal fraction in full. Let me get you started:

0.33333333333333333333333333333
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Have you figured out that you can't exactly represent 1/3 as a finite decimal fraction? In the same way you can't exactly represent 1/10 (base 10) as a finite binary fraction. This seems like a problem, but for almost all real applications for arithmetic it is not an issue. You seldom need more than a few digits of precision for an answer (although for some calculations you may need more precision for intermediate answers).

So the key questions are: what are you trying to do and how much precision do you really need? There are many possible ways to solve your problem, but a solution depends very much on what you are trying to achieve.

HI,

I need some value upto 3 decimal places and want to use that in calculations. But actually the value becomes 22.430000001 like that. in summary I want that value remains 22.43 just not "nice value" to be 'printed'. yes 22.43 and 22.43000001 are almost same. but I need to extract some data from million number of values (which are three decimal place) from text file. So I need exact decimal place or it will be ignored to be extracted.

As suggested I will divide 22430 by 1000, that will be a good option

And if you just want to display it nice, use printf "%.3f\n", $a;. This is covered in perlfaq4

You could use 'sprintf' as part of the loop. Adds some time, but maintains your 3 digits of precision.

perl -e '$n=22.4; for(1..99) { $n = sprintf("%.3f", $n+0.001 ); } prin
+t "Result: $n\n";'
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Hint: Try to think of your numbers as '$n' or '$s' and not '$a'. You'll understand in the future.

Good Luck