Simple math with decimals in PHP

Question

This is killing me! I've never had so much trouble and I can't figure out what I'm doing wrong here.

If I have a number, say 2.32, and I want to do math with it it won't work out. The very simplest example:

$income = $commission; //Commission is 2.32, retrieved from XML echo "income: $income<br>"; $income100 = $income*100; echo "income100: $income100<br>";

The result I get is:

income: 2.32 income100: 200

How can I use a decimal number accurately with math without it changing it?

Thanks so much!

@bigman: Why would you cast it as a string so that it hopefully converts to float... just cast it as a float — prodigitalson
– prodigitalson, Commented Oct 29, 2012 at 20:05
Wow, I didn't realize I made it a string, meant to throw a float. Brain fart — wesside
– wesside, Commented Oct 29, 2012 at 20:06

user142162 · Accepted Answer · 2012-10-29 20:05:35Z

You need to assign $income in the following manner to get rid of the underlying SimpleXMLElement:

$income = (float) $commission;

Example of what happens when you don't:

$x = simplexml_load_string("<a>2.4</a>"); echo $x * 100; // output: 200

Vic · Accepted Answer · 2012-10-29 20:05:21Z

Besides using floats as Tim said, also make sure to use the BC Math functions when performing arithmetic operation on floating point numbers. Specifically bcmul():

$income100 = bcmul($income, 100);

Niet the Dark Absol · Accepted Answer · 2012-10-29 20:07:38Z

The problem with floating-point numbers is that you cannot represent decimal numbers with them (unless it can be written as a/b for integer a and b, and even then only if abs(a) < pow(2,52) and b is a power of 2).

You may be better off using string functions to get an integer value:

$tmp = explode(".",$commission); $tmp = intval($tmp[0].str_pad(substr($tmp[1],0,2),2,"0"));

This will split up the integer part from the decimal part, ensure the decima part is two digits long, and shove it on the end of the integer part, thus effectively multiplying the original number by 100.

No, but I wasn't trying to. There's obviously something going wrong in the conversion to a number that's resulting in the decimal being dropped, but this answer solves that problem.

NappingRabbit · Accepted Answer · 2012-10-29 20:09:40Z

I think the easiest solution would be to cast it to a float with floatval()

$income = floatval($comission)

leave the rest of the code as is and it should work as intended.

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