CODEWITHSUNDEEP
phpoperation
billoo
billoo

Reputation: 115

PHP Addition Subtraction Operation, Not Accurate Result

<?php echo 199.8 + 0.9 -200.7; //expect 0, result 2.8421709430404E-14 ? ?>

Tested on PHP Version 5.3.2-1 ubuntu4.7

Upvotes: 0

Views: 1301

Answers (3)

CSchulz
CSchulz

Reputation: 11020

Here some exact example with http://www.php.net/manual/en/ref.bc.php:

<?php

$a = 199.8;
$b = 0.9;
$c = 200.7;

// set precision
bcscale(1);

$ab = bcadd($a, $b);
echo bcsub($ab, $c); // result 0.0

?>

Tested with PHP 5.3.3-7+squeeze1 on Debian Squeeze

Upvotes: 0

wimvds
wimvds

Reputation: 12850

If you want exact calculations (ie. for monetary transactions) you should use BCD (binary coded decimals) or arbitrary precision math. PHP has support for this using BC Math.

Upvotes: 2

Lightness Races in Orbit
Lightness Races in Orbit

Reputation: 385144

Space-limited, fractional floating point is inaccurate for some values (just in the same way that, in decimal notation, you cannot write out 1/3 in finite space).

2.8421709430404E-14 is very close to 0.

Round it, or output it to a certain number of significant figures.

Upvotes: 7

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