I am trying to calculate this in php :
echo (int)((0.1 + 0.7) * 20);
why it return 15
Expected result: 16
Actual result:15
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almost certain to be a floating point rounding error.Spudley– Spudley2013-09-27 09:56:19 +00:00Commented Sep 27, 2013 at 9:56
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2why do you have jquery tag here ?? removing itbipen– bipen2013-09-27 09:56:23 +00:00Commented Sep 27, 2013 at 9:56
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because some jquery user may help me thatShakti Patel– Shakti Patel2013-09-27 09:57:46 +00:00Commented Sep 27, 2013 at 9:57
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possible duplicate of PHP unexpected result of float to int type castSudhir Bastakoti– Sudhir Bastakoti2013-09-27 09:58:17 +00:00Commented Sep 27, 2013 at 9:58
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1I'm guessing it is because (0.1+0.7) *20 returns 15.9999998 and converting a float to int always rounds downAnton– Anton2013-09-27 09:59:47 +00:00Commented Sep 27, 2013 at 9:59
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10 Answers
From doc: http://php.net/manual/en/language.types.float.php
Floating point numbers have limited precision. Although it depends on the system, PHP typically uses the IEEE 754 double precision format, which will give a maximum relative error due to rounding in the order of 1.11e-16. Non elementary arithmetic operations may give larger errors, and, of course, error propagation must be considered when several operations are compounded.
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....
you can use BC Math Functions
$precision = 2;
echo bcmul( bcadd("0.1","0.7",$precision) ,"20",$precision); // 16.00
Comments
you need
intval ((0.1 + 0.7) * 20);
sorry, it's wrong, but here is a workaround:
$n= ( (0.1 + 0.7) * 20); //=16
$n2 = intval ($n.""); // cast it to string, then to int.
echo $n2;
Type casting the result is leading to a wrong number echo ((0.1 + 0.7) * 20); should give 16
1 Comment
Shakti Patel
yes it working fine but what about floating to integer type casting?
Looks like a rounding error
0.1 + 0.7 = 0.7999999999
0.799999999 * 20 = 15.9999998
int(15.9999998) = 15
you have to round the result.
Comments
did you try this approach? :
<?php
$value = (0.1+0.7)*20;
echo $value;
?>
my result is 16
2 Comments
Shakti Patel
yes it working fine but what about floating to integer type casting?
Butt4cak3
You don't have to cast the result to an integer, because as soon as you print it with echo it gets transformed into its string representation. If you want to round the result, use round().
Please read PHP documentation on foating point numbers. As is written in the documentation,
For example, floor((0.1+0.7)*10) will usually return 7 instead of the expected 8.
When working with floating point numbers, use BC Math to get correct results.
Comments
Comments
Let's be more precise:
printf("%1\$.20f", 0.7); // output: 0.69999999999999995559
printf("%1\$.20f", 0.1); // output: 0.10000000000000000555
printf("%1\$.20f", (0.10000000000000000555+0.69999999999999995559)*20); // output: 15.99999999999999822364
so when you cast the last number to int :
echo (int)15.99999999999999822364; // output: 15
