How to convert string operation into a number?

Question

I have a string '1/2' and i need to get a float value 0.5 from it.

Other examples: Operation: $operation = '5/8'; Wanted value: $value = 0.625;

`list($x, $y) = explode('/', $operation); $value = $x / $y;` — Mark Baker, Mar 05 '15 at 17:44
Probably you're looking for the `eval` function. http://php.net/manual/en/function.eval.php — Andy Lester, Mar 05 '15 at 17:47
possible duplicate of [calculate math expression from a string using eval](http://stackoverflow.com/questions/18880772/calculate-math-expression-from-a-string-using-eval) — Rizier123, Mar 05 '15 at 17:47
Blanket statements like "bad idea to use" aren't helpful in evaluating when one should use them. If you want to help OP, explain the potential problems. — Andy Lester, Mar 05 '15 at 17:48
Or you can try this : http://stackoverflow.com/questions/1015242/how-to-evaluate-formula-passed-as-string-in-php?answertab=votes#tab-top — Niols, Mar 05 '15 at 17:49
If this value is coming from user input, then eval() is potentially a very bad idea.... not only are there security risks with feeding any user input to eval (what if the user inputs `unlink(__FILE__)` or similar), but adequate error handling for malformed input to eval() is also non-existent, making it almost impossible to diagnose problems — Mark Baker, Mar 05 '15 at 17:53
If you want a clean, secure calculator that can handle a range of mathematical expressions (not simply division) then take a look at [how to make a calculator in php](http://stackoverflow.com/questions/12692727/how-to-make-a-calculator-in-php) — Mark Baker, Mar 05 '15 at 17:55

score 4 · Answer 1 · answered Mar 05 '15 at 17:49

4

You can use eval, also please note your are not looking for an int as they are whole numbers.

<?php

$operation = '1/2';

eval('$value = ' . $operation . ';');

echo $value;

?>

answered Mar 05 '15 at 17:49

cmorrissey

`evil()` is not a good idea, since when the input comes from a user he can executes every php code which he wants! – Rizier123 Mar 05 '15 at 17:53
1

@Rizier123 I agree but the OP does not state that the input is coming from a user. – cmorrissey Mar 05 '15 at 17:55
But it's always a security risk! When you don't use it you are sure that it can't be used for bad things. And as far as I know there aren't much places where you really need to use it – Rizier123 Mar 05 '15 at 18:00
@Rizier123 It's not coming from a user. I'm getting it from DB. – Illia Potapchuk Mar 05 '15 at 18:00
@IlliaPotapchuk from the DB and which data do you insert there? user inputs/data?! – Rizier123 Mar 05 '15 at 18:01
@Rizier123 admin inputs data there, but i see what you are talking about. I'll consider "explode" option. – Illia Potapchuk Mar 05 '15 at 19:05

score 1 · Accepted Answer · answered Mar 05 '15 at 17:50

1

This will work if you only have one "/".

$str = '2/5';
$newStr = explode('/', $str);
echo $newStr[0]/$newStr[1];

answered Mar 05 '15 at 17:50

SebHallin

Mateusz Mania · Answer 3 · 2015-03-05T17:59:57.620

-1

Edited. Not elegant because eval is used, but working.

$operation = '1/2';

function stringCalc($operation){

    return eval('return '.$operation.';');
}

$value = stringCalc($operation);

edited Mar 05 '15 at 17:59

answered Mar 05 '15 at 17:45

Mateusz Mania

Sorry. Answer edited, my second solution. Okay, now i see other user gives You same solution ... – Mateusz Mania Mar 05 '15 at 18:02
Btw. I found few questions, like this. http://stackoverflow.com/questions/14999578/php-calculate-formula-in-string http://stackoverflow.com/questions/5057320/php-function-to-evaluate-string-like-2-1-as-arithmetic-2-1-1 http://stackoverflow.com/questions/18880772/calculate-math-expression-from-a-string-using-eval http://stackoverflow.com/questions/25469528/convert-string-into-math-equation http://stackoverflow.com/questions/28586982/risks-of-using-php-eval-for-string-math http://stackoverflow.com/questions/1015242/how-to-evaluate-formula-passed-as-string-in-php Maybe You found better answer. – Mateusz Mania Mar 06 '15 at 01:04

3 Answers3