Why Does PHP Floating-Point Addition Produce Unexpected Results?

PHP Floating Number Precision: Why the Unexpected Result?

PHP's handling of floating-point numbers can produce surprising results. Consider the following:

$a = '35';
$b = '-34.99';
echo ($a + $b);

Instead of the expected 0.01, the output is 0.009999999999998. This peculiarity stems from the fundamental difference between floating-point arithmetic and real number arithmetic.

Floating-point numbers, as their name suggests, represent numbers using binary notation with finite precision. As a result, it's impossible to accurately represent all numbers using this method. This can lead to inaccuracies and surprises like the one above.

To address this issue, one can consider the following:

• Use round($result, 2) on the result to round it to 2 decimal places.
• Utilize integers. If dealing with currency, store $35.00 as 3500 and $34.99 as 3499, then divide the result by 100.

Unfortunately, PHP lacks a dedicated decimal datatype like many other languages. This can hinder precision when working with financial or scientific calculations.

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