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Bug #46727 For loop doesn't work as expected with decimals
Submitted: 2008-12-01 21:11 UTC Modified: 2008-12-02 05:47 UTC
From: grant at tattomedia dot com Assigned:
Status: Not a bug Package: Unknown/Other Function
PHP Version: 5.3CVS-2008-12-01 (snap) OS: Linux
Private report: No CVE-ID: None
View Developer Edit
 [2008-12-01 21:11 UTC] grant at tattomedia dot com 
Description:
------------
My PHP version is PHP 5.2.5 (cli):  This wasn't listed in the select.

It seems that a for loop that deals with floats has bad logic when evaluating equivalence against another number (in my situation an int).



Reproduce code:
---------------
$values = array();
for ($val = 0; $val <= 2; $val = $val + .1) {
    $values[] = $val;
}
print_r($values);

Expected result:
----------------
Array ( [0] => 0 [1] => 0.1 [2] => 0.2 [3] => 0.3 [4] => 0.4 [5] => 0.5 [6] => 0.6 [7] => 0.7 [8] => 0.8 [9] => 0.9 [10] => 1 [11] => 1.1 [12] => 1.2 [13] => 1.3 [14] => 1.4 [15] => 1.5 [16] => 1.6 [17] => 1.7 [18] => 1.8 [19] => 1.9 [20] => 2 ) 

Actual result:
--------------
Array ( [0] => 0 [1] => 0.1 [2] => 0.2 [3] => 0.3 [4] => 0.4 [5] => 0.5 [6] => 0.6 [7] => 0.7 [8] => 0.8 [9] => 0.9 [10] => 1 [11] => 1.1 [12] => 1.2 [13] => 1.3 [14] => 1.4 [15] => 1.5 [16] => 1.6 [17] => 1.7 [18] => 1.8 [19] => 1.9 )

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 [2008-12-02 05:44 UTC] magicaltux@php.net 
This is because at the last iteration, the value for $val is (at least on my 5.2.6 test system; php 5.3.0 returns me the same value):

2.000000000000000444089209850062616169452667236328125

This is > 2, which means "<= 2" is false.

If I dump the values of $val for each iteration:

0
0.1000000000000000055511151231257827021181583404541015625
0.200000000000000011102230246251565404236316680908203125
0.3000000000000000444089209850062616169452667236328125
0.40000000000000002220446049250313080847263336181640625
0.5
0.59999999999999997779553950749686919152736663818359375
0.6999999999999999555910790149937383830547332763671875
0.79999999999999993338661852249060757458209991455078125
0.899999999999999911182158029987476766109466552734375
0.99999999999999988897769753748434595763683319091796875
1.0999999999999998667732370449812151491641998291015625
1.1999999999999999555910790149937383830547332763671875
1.3000000000000000444089209850062616169452667236328125
1.4000000000000001332267629550187848508358001708984375
1.5000000000000002220446049250313080847263336181640625
1.6000000000000003108624468950438313186168670654296875
1.7000000000000003996802888650563545525074005126953125
1.8000000000000004884981308350688777863979339599609375
1.9000000000000005773159728050814010202884674072265625

Your "best" option would be to round($val, 1) before checking, but it might prove to be expensive. This is why it's always tricky to work with float values.
 [2008-12-02 05:47 UTC] magicaltux@php.net 
Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/en/language.types.float.php and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php
 
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