#29516 [Opn->Bgs]: Mathematical calculations give unexpected result

ID: 29516 Updated by: derick@php.net Reported By: beckwest22 at yahoo dot com -Status: Open +Status: Bogus Bug Type: Math related Operating System: Windows XP PHP Version: 5.0.0 New Comment: Floating point values have a limited precision. Hence a value might not have the same string representation after any processing. That also includes writing a floating point value in your script and directly printing it without any mathematical operations. Thank you for your interest in PHP. . Previous Comments: ------------------------------------------------------------------------ [2004-08-04 05:49:08] beckwest22 at yahoo dot com Description: ------------ I have been reading that doing some mathematical calculations with floats and integers in php gives some unexpected results. I am not sure if this is a bug or not. When I do a combination of division and subtraction with the number 19, I get unexpected results. I would appreciate any light you could shine on this subject. Modules compiled with PHP: I did not compile any modules with PHP. The only thing different in my php.ini file is that I uncommented the extension=php_mysql.dll line in the file. Reproduce code: --------------- <?php $num = 19; $res = $num/10; echo $res; echo "<br>"; $res1 = ($num%10)/10; echo $res1; echo "<br>"; $res2 = $res - $res1; echo $res2; $final_result = $res2 - 1; echo "<br>"; echo $final_result; ?> Expected result: ---------------- This is what I expect from the calculations: $res = 19/10; // equals 1.9 $res1 = (19%10)/10; // equals 0.9 $res2 = 1.9 - 0.9; // equals 1 $final_result = 1 - 1; // equals 0 expected $final_result to be 0 Actual result: -------------- $final_result equals -1.11022302463E-016 ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=29516&edit=1