how do i make a user-input math expresstion

I'm a math teacher, I've made an online homework submission page. I want students to be able to submit answers, and then use php to check their answers, and give them a grade.

I can check answers that are numbers, like "2", "-9" or "12.35".

But I also want to check answers that are equations. on one problem the answer was "2a + 50", to check it i took in the user input as a string, and then I wrote out all different ways of writing it. Such as "50 + 2a", "a2 + 50" etc...

I want to be able to take a user-input as an expression. for example if I was in the code and I wrote:

$a = 1.2 // any number, just to give $a a numeric value
2*$a + 50 == 50 + $a*2

It would return true.

But i only know how to take user input as strings or numbers, for example:

$a = 1.2
"2*$a + 50" == 50 + $a*2

It would return false because the left side is a string.


It would be possable to take the user input as a string and "explode" it into an array then make it into an expression, but that would be alot of work. I'm hoping there's a better way, or maybe someone already made a function i can use.


how do i make a user-input math expresstion?

please help

 

<?php
$v = '1'; //set v to 1 for eaiser computation
$argument = '2*$a + 50 == 50 + $a*2';

list($left,$right) = explode('==',$argument);

/* right side */
$finalright = keep_braking($right);

$finalleft = keep_braking($left);

if($finalright == $finalleft ){ echo 'correct';}else{echo 'incorrect';}
?>

PHP:

I might write the keep_braking for you tomorrow.

Peace,

 

thanks azizny,

It looks like you are saying there is no simple way of doing it, a function that explodes the string and looks for each operator is needed. I was hoping there was a better way. but if you actually write the "keep_braking" I would really appreciate it.