Calculate a sum in a string

Question

I have string like this: $string = "a + b + c";. Now I would like to calculate the string as sum.

For example:

$a = 10;
$b = 10;
$c = 10;
$string = "a + b + c";

echo "Result is ".$string;
output-> Result is 30

$string = "a + b * c";

echo "Result is ".$string;
output-> Result is 110

Thanks in advance

Sjoerd · Answer 1 · 2013-03-27T07:58:26.593

3

I once made a calculator script.

It parses the calculation and puts each number and operator on a stack, in reverse polish notation.
It calculates the results by executing operations all operations on the stack.

edited Mar 27 '13 at 07:58

answered Mar 17 '11 at 10:05

Sjoerd

74,049
16
131
175

This is the best solution I've seen that doesn't use eval(). Could use an update though, a few of the examples didn't work. Worked fine for most equations though. – jchavannes Mar 26 '13 at 20:38

score 3 · Answer 2 · edited May 23 '17 at 11:55

3

Your question may already have been answered here on StackOverflow:

How to evaluate formula passed as string in PHP?

edited May 23 '17 at 11:55

Community

1
1

answered Mar 17 '11 at 10:09

Cogicero

1,514
2
17
36

score 2 · Answer 3 · answered Mar 17 '11 at 10:35

My standard answer to this question whenever it crops up:

Don't use eval (especially as you're stating that this is user input) or reinvent the wheel by writing your own formula parser.

Take a look at the evalMath class on PHPClasses. It should do everything that you're asking, in a safe sandbox.

Michiel Pater · Accepted Answer · 2011-03-17T11:06:50.910

1

The variables in your string are missing the dollar signs. I wrote and tested a script for you that adds these signs to the variables and then parses the string as PHP code using the function eval().

$a = 10;
$b = 10;
$c = 10;
$string = "a + b + c";

$result = eval('return ' . preg_replace('/([a-zA-Z0-9])+/', '\$$1', $string) . ';');
echo $result;

This will output 30.

edited Mar 17 '11 at 11:06

answered Mar 17 '11 at 10:07

Michiel Pater

22,377
5
43
57

You can use `return` in eval statements. – ThiefMaster Mar 17 '11 at 10:09
@Michiel Pater is it possible with `$string = "a+b+c";` then in code `eval('return ' . preg_replace('/([a-zA-Z0-9])+/', '\$$1', $string));` – no_freedom Mar 17 '11 at 10:30
@user559744: Yes, that is possible. – Michiel Pater Mar 17 '11 at 10:37
@Michiel Pater working great. why you add `;` at end of the string? – no_freedom Mar 17 '11 at 11:00
@user559744: Nice, that was a mistake. I have updated the code. – Michiel Pater Mar 17 '11 at 11:07
@Michiel Pater can you help me again? I changed the string format `$string = "aa + ba + cx";` and your code does not support that string format. thanks any ways – no_freedom Mar 17 '11 at 13:43
It should be `([a-zA-Z0-9]+)` instead of `([a-zA-Z0-9])+` – ThiefMaster Mar 17 '11 at 14:11

score 0 · Answer 5 · answered Mar 17 '11 at 10:05

0

you can do:

$string = "$res = $a + $b + $c;";
eval($string)
echo($res);

answered Mar 17 '11 at 10:05

heximal

10,327
5
46
69

Calculate a sum in a string

5 Answers5

Linked

Related