3:03pm, Aben Siatris wrote:
> > : my $number=(0.75-0.54)/0.03;
> > : print "$number\n";
> > : for (0..$number)
> > : {
> > : print "$_ / $number\n";
> > : }
> > :
> > : my $number=(75-54)/3;
> > : print "$number\n";
> > : for (0..$number)
> > : {
> > : print "$_ / $number\n";
> > : }
> > :
> > : output:
> > : 7
> > : 0 / 7
> > : 1 / 7
> > : 2 / 7
> > : 3 / 7
> > : 4 / 7
> > : 5 / 7
> > : 6 / 7
> > : 7
> > : 0 / 7
> > : 1 / 7
> > : 2 / 7
> > : 3 / 7
> > : 4 / 7
> > : 5 / 7
> > : 6 / 7
> > : 7 / 7
>
> at first is 'FOR' from 0..7 and output prints 0..6
> at second is 'FOR' from 0..7 and output prins 0..7
>
> it is normal?
>
The first time through, Perl is working with floating-point numbers, but the
second time, it is dealing with integers, so there are no rounding errors.
You can see the difference in this simpler example:
# perl -e'$number=(0.75-0.54)/0.03;$number=int($number);printf("%f\n",$number);'
6.000000
# perl -e'$number=(75-54)/3;$number=int($number);printf("%f\n",$number);'
7.000000
To see the root of the problem:
# perl -e'$number=(0.75-0.54)/0.03;;printf("%.20g\n",$number);'
6.9999999999999991118
# perl -e'$number=(75-54)/3;;printf("%.20g\n",$number);'
7
The rounding errors caused by using floating point math are causing the
difference.
In a strongly-typed language, this would be more obvious ('cause you would
have had to declare your variable as a float in the first place), but you
would still have the same problem.
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