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 =          


        

Answer 1

Your question may already have been answered here on StackOverflow:

How to evaluate formula passed as string in PHP?

Answer 2

you can do:

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

Answer 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.

Answer 4

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.

Answer 5

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.