php calculate formula in string [duplicate]

问题

So I have formula as string

$comm = "(a x 5% - 2%)";

I want it to be $comm = $a * 5/100 * (1-2/100);

How can I do this in php?

回答1:

To do this the right way, reliably and safely, from scratch, you will need to perform:

Lexical analysis, this involves pattern matching the input with tokens:
```
(a x 5% - 2%)
```
would become something like the following chain of tokens:
```
openparen variable multiply integer percent minus integer percent closeparen
```
Syntax analysis, this involves taking those tokens and defining the relationships between them, something like this, matching up the patterns of tokens:
```
statement = operand operator statement
```
Then you will need to parse the resulting syntax tree so that you can run it and produce the answer.

It won't ever look as simple as $comm = $a * 5/100 - 2/100; but it will result in the same conclusion.

Someone somewhere has already likely had a go at this problem, here's two I found after a brief Google search: PHP Maths Expression Parser, And another.

These SO questions are similar as well Smart design of a math parser?, Process mathematical equations in php

回答2:

Take a look at

http://www.phpclasses.org/package/2695-PHP-Safely-evaluate-mathematical-expressions.html

Which can evaluate Math Code

 // instantiate a new EvalMath
  $m = new EvalMath;
  $m->suppress_errors = true;
 // set the value of x
  $m->evaluate('x = 3');
   var_dump($m->evaluate('y = (x > 5)'));

Found at: Process mathematical equations in php

回答3:

It just trying, but maybe good start.

$somm = 0;
$a = 30;

$str = "(a x 5% - 2%)";

$pt1 = "/x/i";
$str = preg_replace($pt1, "*", $str);

$pt2 = "/([a-z])+/i";
$str = preg_replace($pt2, "\$$0", $str);

$pt3 = "/([0-9])+%/";
$str = preg_replace($pt3, "($0/100)", $str);

$pt4 = "/%/";
$str = preg_replace($pt4, "", $str);

$e = "\$comm = $str;";
eval($e);
echo $e . "<br>";
echo $comm;

回答4:

Solved!!

<?php 
    function evalmath($equation)
    {
        $result = 0;
        // sanitize imput
        $equation = preg_replace("/[^a-z0-9+\-.*\/()%]/","",$equation);
        // convert alphabet to $variabel 
        $equation = preg_replace("/([a-z])+/i", "\$$0", $equation); 
        // convert percentages to decimal
        $equation = preg_replace("/([+-])([0-9]{1})(%)/","*(1\$1.0\$2)",$equation);
        $equation = preg_replace("/([+-])([0-9]+)(%)/","*(1\$1.\$2)",$equation);
        $equation = preg_replace("/([0-9]{1})(%)/",".0\$1",$equation);
        $equation = preg_replace("/([0-9]+)(%)/",".\$1",$equation);
        /*if ( $equation != "" ){
            $result = @eval("return " . $equation . ";" );
        }
        if ($result == null) {
            throw new Exception("Unable to calculate equation");
        }
        return $result;*/
        return $equation;
    }
    $total = 18000;
    $equation =  evalmath('total-(230000*5%-2%+3000*2*1)');
    if ( $equation != "" ){

        $result = @eval("return " . $equation . ";" );
    }
    if ($result == null) {

        throw new Exception("Unable to calculate equation");
    }
    echo $result;
?>

来源：https://stackoverflow.com/questions/14999578/php-calculate-formula-in-string

标签

php

formula

equation