Can anyone tell me why: 

perl -e 'print -8 + -15 * 0.5, "\n";'

-15.5

[download]

does the right thing, and multiplies -15 times 0.5, then adds it (-7.5) to -8 to get -15.5, but: 

print "LEQ/REQ: $leftEq[$_[0]][$i] $rightEq[$_[0]][$i]\n";
($leftEq[$_[0]][$i], $rightEq[$_[0]][$i]) =
    ($leftEq[$_[0]][$i] + $leftStorDelta[$i] * $factor,
    $rightEq[$_[0]][$i] + $rightStorDelta[$i] * $factor);
print "Fct: $factor Delt: $leftStorDelta[$i] $rightStorDelta[$i]\n";
print "Post-LEQ/REQ: $leftEq[$_[0]][$i] $rightEq[$_[0]][$i]\n\n";

[download]

gives output like this: 

LEQ/REQ: -8 -8
Fct: 0.50 Delt: -15 -15
Post-LEQ/REQ: -8 -8

[download]

even though it should be the same darn thing. From what I can gather, it's treating $factor (0.5) like an integer, multiplying -8 by 1.

...but why?

It should be noted that I only need two decimal places of precision in the answer, so if there's a way I can avoid the whole floating point jungle and just deal with decimal numbers of a form \d.\d\d, that would be more than fine.

My main question is why I'm not getting any decimal precision at all when I multiply times $factor, yet it works just fine with constants in a 'perl -e' one-liner.

In reply to Floating point hell by DcmbrAgnt

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