in reply to Coping with decimals

several ways come to my mind. 
my $phase;
my $number = 2.543;

#substr
$phase = "0" . substr($number,index($number,"."));

#regex
$number =~ /(\..+)/;
$phase = "0$1";


#int
$phase = $number-int($number);

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holli, /regexed monk/

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Re^2: Coping with decimals
by polettix (Vicar) on Jun 02, 2005 at 10:50 UTC
    If the number doesn't contain a decimal part, you could end up using $1 from a previous match. I'd suggest (maybe some parenthesis can be avoided, but I'm not able to test ATM): 
    $phase = '0' . (($number =~ /(\..+)/) ? $1 : '');

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    I found particularly wit to include the "." inside $1, in order to avoid repetition.

    Flavio (perl -e 'print(scalar(reverse("\nti.xittelop\@oivalf")))')

    Don't fool yourself.
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Re^2: Coping with decimals
by mikeraz (Friar) on Jun 02, 2005 at 11:09 UTC

    I can't agree with your solution. The questioner is calculating a phase. Doing math. Your solution is based on string manipulation. Conflating text values and numeric values leads to errors. Refrain from smearing your mental map of a problem space.

    Be Appropriate && Follow Your Curiosity
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      The standard Perl approach to rounding numbers (with sprintf) amounts to using a string manipulation for what is arguably an arithmetic task. Did you have any particular error in mind?

      When I first saw the question, the two solutions I thought of were $x - int( $x ) or indeed something along the lines of $x =~ s/\d+(?=\.)//, and I'm curious about what errors could have resulted from the latter approach.

      the lowliest monk

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        A loss of precision: 

        #! perl -slw
use strict;

my $pi = 3.141592653589793238462643383279502;

print $pi - int( $pi );

( my $fract = $pi ) =~  s/\d+(?=\.)//;

print $fract;
__END__
P:\test>462902
0.141592653589793
.14159265358979

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        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
        "Science is about questioning the status quo. Questioning authority".
        The "good enough" maybe good enough for the now, and perfection maybe unobtainable, but that should not preclude us from striving for perfection, when time, circumstance or desire allow.
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[d/l]

        Having a mental map that considers strings numbers and numbers strings allows one to make subtle errors in their programs.

        In fact, sprintf returns a string after doing an arithmatic operation. Compare a 2 deciaml point operation via sprintf: 

        my $num = 4.62899;
$round = sprintf "%.2f", $num;
print "$round\n";

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        prints 4.63, which is not a trimming of the string to two decimal places.

        For another example consider this snip and output. 

        my $string = "0.0";
print "string $string is ", ($string ? "True" : "False"), "\n";
print "string $string is ", ($string+0 ? "True" : "False"), "\n";

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        Which prints:
        string 0.0 is True
        string 0.0 is False

        Be Appropriate && Follow Your Curiosity
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