Parse math operations with PHP

Question

I am working on a project where I need to make a function that will parse the 4 default math operations (addition, subtraction, multiplication, division). It would be nice i

Answer 1

You could use eval() (WARNING: be sure what enters is a math operation and not some other arbitrary input or php code).

$input = "3 + (4 - 2 * 8) / 2";

eval('$result = ' . $input . ';');

echo "The result is $result";

Answer 2

if you want a truly safe math parser, then eval won't do it. bcParserPHP can do it. It is implemented in PHP and does not use eval, thus it is very secure.

Answer 3

This should be pretty secure:

function do_maths($expression) {
  eval('$o = ' . preg_replace('/[^0-9\+\-\*\/\(\)\.]/', '', $expression) . ';');
  return $o;
}

echo do_maths('1+1');

Answer 4

Regular expressions aren't the answer here; I suggest using an expression tree where all terminal nodes are constants or variables, and the rest of the nodes are operators. For example, 2 + 3 * 4 becomes:

+ --- 2
  |
  --- * --- 3
        |
        --- 4

Then, you evaluate the expression by using a depth-first traversal. In PHP it's sort of difficult to represent trees, but you could either use a built-in library as a commenter suggested or represent them using an associative array of arrays.

Answer 5

there was a similar problem
How to evaluate formula passed as string in PHP? you can try to use Class: Eval Math from php classes http://www.phpclasses.org/package/2695-PHP-Safely-evaluate-mathematical-expressions.html

Answer 6

I can recommend https://github.com/andig/php-shunting-yard which is a PSR-0 compatible implementation of the Shunting Yard algorithm.