CODEWITHSUNDEEP
php
davco98
davco98

Reputation: 31

Use my php variable as a formula to calculate something

I'm working in an invoice system, that has to calculate different formulas for every product, which will need to be filled with Width, Height, and Material cost.

I did a database where i'm storing 

t_title -> "Curtain 1"

t_formula -> "({ANCHO}*{ALTURA})*{PRECIO}"

and then php does this:

<?php 
   $ancho = str_replace("{ANCHO}", $_POST['ancho'], $articulo['t_formula']);
   $alto = str_replace("{ALTURA}", $_POST['alto'], $ancho);
   $precio = str_replace("{PRECIO}", $_POST['precio'], $alto);
   $total = $precio; echo eval($total);
?>

and the result is not giving anything, but a blank space.

How can i make it to work? I know that php can't calculate from variables as php but, i can't find another way to do it.

Upvotes: 0

Views: 1990

Answers (2)

Ananth
Ananth

Reputation: 4407

The eval() function expects the string parameter to be a proper code statement.

$str = '(10*10) * 1000';
echo eval($str);

will give you an error, because php cannot evaluate that string. However,

$str = 'return (10*10) * 1000;';
echo eval($str);

will evaluate the expression correctly.

You should use:

$total = 'return ' . $precio . ';';
echo eval($total);

Upvotes: 1

SaidbakR
SaidbakR

Reputation: 13552

Your using eval is wrong. The string passed to eval must be valid PHP code. i.e:

$precio2 = '$total = '.$precio.';';
eval($precio2);
echo $total;

http://php.net/manual/en/function.eval.php

Upvotes: 0

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