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Adding two numbers in PHP getting unexpected results, such as this

$a=115.40;
$b=120.25;
$c=4.85;
echo ($a-$b)+$c;

results in

-5.3290705182008E-15

these numbers maybe integers or floats

Mehar
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  • what results were u expecting? – Masivuye Cokile May 12 '17 at 13:17
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    what does $a, $b and $c equal? What are they defined as – treyBake May 12 '17 at 13:17
  • @ThisGuyHasTwoThumbs question updated – Mehar May 12 '17 at 13:24
  • Due to the nature of how folating-points works in computing in general, they are not going to be exactly the result you expect. What you're seeing now is that the floating-point is *about* zero, but not exactly zero. You can format it to be zero, example: https://3v4l.org/P70iL – Qirel May 12 '17 at 13:24
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    `sprintf('%6.3f',($a-$b)+$c);` equals 0 – RiggsFolly May 12 '17 at 13:28
  • (115.40 - 120.25) + 4.85 = 0 - for floats you need to use more complicated functions then + - etc. http://stackoverflow.com/questions/17210787/php-float-calculation-error-when-subtracting - see second answer for explanation – treyBake May 12 '17 at 13:38

1 Answers1

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If you add floats, you can have solutions like that. Please check Manual:

Additionally, rational numbers that are exactly representable as floating point numbers in base 10, like 0.1 or 0.7, do not have an exact representation as floating point numbers in base 2, which is used internally, no matter the size of the mantissa. Hence, they cannot be converted into their internal binary counterparts without a small loss of precision. This can lead to confusing results: for example, floor((0.1+0.7)*10) will usually return 7 instead of the expected 8, since the internal representation will be something like 7.9999999999999991118....

Alon Eitan
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timiTao
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