Calculating an Equation Stored in a String

[d_mc_a]

Sorry if this has already been answered before but it is a hard problem to find an answer for.  I am making a simple web-based interface that will allow users to add shapes into a DB.  This will involve uploading a shape description, a jpeg of the shape and an equation for the area of the shape.  It doesn't have to be too dynamic so i've kept the equation as a standard format, using x0 -> xn as the variables for the equation.  For example, the equation for the area of a square would be x0 * x0 ( length * length ) as there is only one variable for deriving the area of a square.  A rectangle would be x0 * x1 ( length * height ) etc.  I then have code that reads the equation and counts how many variables, assigns names to these variables etc.  This part is all fine. 

 

When the user selects a rectangle and enters 2 as variable1 and 3 as variable2, the code will retrieve x0*x1 as the rectangle's equation, replace the x0 with 2 and x1 with 3, using str_replace() function.  This all works fine.  So, I'm left with a string stored under a variable with value 2*3  The only problem is that i don't know how to calculate that string.  I don't know how i would return a value of 6.  Will it not always return the value as "2*3" because it is a string?!?

 

God, i hope this isn't a stupidly simple solution 

 

Any help would be appreciated

[utexas_pjm]

Use the eval function. 

 

<?php
eval('$sum = 1 + 1;');
echo $sum;
// prints 2
?>

 

Best,

 

Patrick

[d_mc_a]

Excellent, Thanks alot. In case anyone else is interested, I used:

 

eval('$result = '.$Equation.';');
echo $result;

 

Where $Equation = "2*2";

 

Thanks again