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Hi I've been having a problem rounding numbers to -0 instead of just a 0
code:
<?php
$num= 0.000000031;
$round = number_format((float)$num, 1, '.', '');
echo $round * -1;
?>
output: -0
expected output: 0
I've been looking to any solution but nothing found.
kindly explain & help me why it rounds up to -0 instead of 0? thank you
574
Example #1 round() examples php echo round(3.4); // 3 echo round(3.5); // 4 echo round(3.6); // 4 echo round(3.6, 0); // 4 echo round(1.95583, 2); // 1.96 echo round(1241757, -3); // 1242000 echo round(5.045, 2); // 5.05 echo round(5.055, 2); // 5.06 ?>
Use number_format() Function to Show a Number to Two Decimal Places in PHP. Use round() Function to Show a Number to Two Decimal Places in PHP. Use sprintf() Function to Show a Number to Two Decimal Places in PHP.
There are certain rules to follow when rounding a decimal number. Put simply, if the last digit is less than 5, round the previous digit down. However, if it's 5 or more than you should round the previous digit up. So, if the number you are about to round is followed by 5, 6, 7, 8, 9 round the number up.
Not the rounding makes it -0.
The $round variable contains this before the last line:
string(3) "0.0"
You can verify this with adding this line:
var_dump($round);
before the echo.
So if you multiply "0.0" (string) with -1 then the result will be "-0"
Because (string)0 is casted to (float)0 before the multiplication and
(float)0 * -1 = -0
php5 -r 'var_dump((float)0*-1);'
float(-0)
Which is completely normal based on the floating numbers behaviour. (More details: http://en.wikipedia.org/wiki/Signed_zero )
If this is a problem you can add 0 to avoid this "magic":
php5 -r 'var_dump((float)0*-1+0);'
float(0)
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