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 if the function could parse operations between brackets.

So, a must is that the function first check for multiplication and division operations (should check for that after it parser all operations between brackets if they exist, and that rule should apply for bracket operations [the biggest problem is that the brackets can contain brackets]). After doing all multiplication and division operations, it should do all addition and subtraction operations. The final number should be returned by functions.

Another nice addition would be a RegExp string that will check for math operations.

Thanks in advance!

For your parenthesis problem : you should learn recursion to learn recursion — Matthieu Napoli, Apr 27 '11 at 11:59
The 'question' starts out with "I am working on a project" but quickly becomes a wish-list of features. — pavium, Apr 27 '11 at 12:05
Sounds like a homework problem to me. Is this a homework problem? — KyleWpppd, Apr 27 '11 at 12:13
maybe math parser will help http://stackoverflow.com/questions/1015242/how-to-evaluate-formula-passed-as-string-in-php — Fivell, Apr 27 '11 at 12:13

score 6 · Accepted Answer · answered Apr 27 '11 at 14:31

6

This should be pretty secure:

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

echo do_maths('1+1');

answered Apr 27 '11 at 14:31

dave1010

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what should i have to change if i have to support floating numbers too?/ – Ahesanali Suthar Dec 17 '15 at 03:15

score 2 · Answer 2 · answered Apr 27 '11 at 14:18

2

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";

answered Apr 27 '11 at 14:18

Carlos Campderrós

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I wonder if it would be possible to make an eval() 100% safe for math expressions if you were to check for any unrecognized character; i.e. `preg_replace('~[^0-9.()-+*/]~', '', $input);` – Martijn Jan 16 '14 at 16:11
@Martijn probably that would work, and is the method used in the accepted answer as well. – Carlos Campderrós Jan 17 '14 at 08:42

score 2 · Answer 3 · edited May 23 '17 at 12:06

2

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

edited May 23 '17 at 12:06

Community

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answered Apr 27 '11 at 14:34

Fivell

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Link-only answer – mickmackusa Jul 18 '18 at 11:21

score 1 · Answer 4 · answered Jan 17 '14 at 07:33

1

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

answered Jan 17 '14 at 07:33

andig

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score 0 · Answer 5 · answered Apr 27 '11 at 14:29

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.

score 0 · Answer 6 · answered Jul 21 '11 at 16:22

0

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.

answered Jul 21 '11 at 16:22

Henry

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Parse math operations with PHP

6 Answers6

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