Simple math with decimals in PHP

问题

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!

回答1:

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

回答2:

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);

回答3:

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.