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Re: Problems with number resolution

by poj (Monsignor)
on Jan 01, 2018 at 17:20 UTC ( #1206516=note: print w/replies, xml ) Need Help??

in reply to Problems with number resolution

Hold the sum as an integer.

my @nr = (32431.19, 20, -10, -31800); my $x = 0; for (@nr) { $x += $_*100; print "$_ => ".($x/100)."\n"; }

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Re^2: Problems with number resolution
by Anonymous Monk on Jan 01, 2018 at 19:14 UTC

    Thanks Poj,

    To have the sum as integer, the (number*100) has to be converted to an integer using round.
    use Math::Round qw/round/; my @nr=('32431.19', '20', '-10', '-31800'); my $x=0; foreach (@nr) { $x+=round($_*100); print "$_ => ".$x/100 ."\n"; }
      Why do you use round here? I don't think you need it. Or can your input numbers have more than two decimals? I think you said that there could be only two decimal places.

      Another point is that I don't see any reason to print incremental results each time through the look (except possibly for debugging purposes). Put the print statement after the end of the foreach loop.

      And you might want to use printf instead of print in this specific case. In fact, using printf might be the only change that you need in your original code, as shown with this example under the Perl debugger:

      DB<1> @nr=('32431.19', '20', '-10', '-31800'); DB<2> $x=0; DB<3> $x += $_ for @nr; DB<4> print $x 641.189999999999 DB<5> printf '%.2f', $x; 641.19

        The numbers have maximum 2 digits. The code is just for debugging, extracting the problem from a larger code, to have some small code to play. In the original code all sums are stored in an array and used later. Therefore printf is only a solution for the small debug code.

        You need the round. The effect is much more seldom when using *100, but still exists. Please see:
        my @nr=('34455.28','-33907.55'); my $x=0; foreach (@nr) { $x+=($_*100); print "$_ => ".$x/100 ."\n"; } 34455.28 => 34455.28 -33907.55 => 547.729999999995

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