Evaluate a string formula?

[ilarika]

How to implement PHP code that calculates a formala which has been created from substring.

E.g

$formula_str = "[value1]+100"

$formula = str_replace("[value1]", "2", $formula_str);

How can the value of formula can evaluate from string variable(eg. "2+100")? Any ideas?

[PHPThorsten]

eval() will do the job:

$formula_str = "[value1]+100";

$formula_str = str_replace("[value1]", "2", $formula_str);

$formula_str = "\$res = $formula_str ;";

eval($formula_str);

echo $res;