php round not working when I use float 7 / 100

Question

My code is very simple, for example, my php version is 5.5.11, this is my sample code:

$result = round(($num / 100), 2); // 0.070000000001
$result = $num / 100; // 0.070000000001

I get the $result is 0.070000000001, and if $num = 3, the $result is correct. And I used var_dump($num), the type is the float. how can I fix it?

edit

I found the reason, but I'm not sure the detail. I use Codeigniter, and I load a library PHPExcel, this is third party lib, when I load it, and I will have this problem, but I'm not sure the reason detail.

it is connected with how float digits are stored in PC memory — Robert, Nov 06 '15 at 11:53
There's nothing wrong with it. The exact format can only be achieved with strings, use http://php.net/number_format — Karoly Horvath, Nov 06 '15 at 11:56
My code had a lot of logic, I can't show a lot of codes, and I want to know what reason will cause this problem. — lighter, Nov 06 '15 at 11:57
then read my answer and go to see link in manual. There is large red box that explains it deeply. — Robert, Nov 06 '15 at 11:58
I founded the problem, cause I use Codeigniter, and I load `PHPExcel` package, and I didn't load this package, it's work. But I don't know why? — lighter, Nov 06 '15 at 12:07

score 1 · Accepted Answer · answered Nov 06 '15 at 11:56

As I wrote in comment it is connected with how floats are stored in memory

From manual:

Never trust floating number results to the last digit, and do not compare floating point numbers directly for equality. If higher precision is necessary, the arbitrary precision math functions and gmp functions are available.

http://php.net/manual/en/language.types.float.php

I don't know what you want to do with this float variable but if you want to compare then you need some $epsilon

if(abs($a-$b) < $epsilon)

if you want to round then probably you should ignore last digit. number_format() seems like better solution.

score 0 · Answer 2 · answered Nov 06 '15 at 12:02

This is the issue with floating numbers.

You can even try bccomp

    $a = 1.2 * 3;
    if (bccomp($a, 3.6) === 0) {
        echo 'equal';
    } else {
        echo 'not equal';
    }

    //echoes equal

    echo "----------------------";
    $a = 1.2 * 3;
    if ($a == 3.6) {
        echo 'equal';
    } else {
        echo 'not equal';
    }

    //echoes not equal

php round not working when I use float 7 / 100

2 Answers2