Test of clarkk's Field_calculate

Field_calculate.php

<?php
/**
* Class provided by http://stackoverflow.com/users/555222/clarkk
* in this answer http://stackoverflow.com/a/27077376
*/
class Field_calculate {
    const PATTERN = '/(?:\-?\d+(?:\.?\d+)?[\+\-\*\/])+\-?\d+(?:\.?\d+)?/';

    const PARENTHESIS_DEPTH = 10;

    public function calculate($input){
        $input = str_replace(' ','',$input);
        if(strpos($input, '+') != null || strpos($input, '-') != null || strpos($input, '/') != null || strpos($input, '*') != null){
            //  Remove white spaces and invalid math chars
            $input = str_replace(',', '.', $input);
            $input = preg_replace('[^0-9\.\+\-\*\/\(\)]', '', $input);

            //  Calculate each of the parenthesis from the top
            $i = 0;
            while(strpos($input, '(') || strpos($input, ')')){
                $input = preg_replace_callback('/\(([^\(\)]+)\)/', 'self::callback', $input);

                $i++;
                if($i > self::PARENTHESIS_DEPTH){
                    break;
                }
            }

            //  Calculate the result
            if(preg_match(self::PATTERN, $input, $match)){
                return $this->compute($match[0]);
            }

            return 0;
        }

        return $input;
    }

    private function compute($input){
        $compute = create_function('', 'return '.$input.';');

        return 0 + $compute();
    }

    private function callback($input){
        if(is_numeric($input[1])){
            return $input[1];
        }
        elseif(preg_match(self::PATTERN, $input[1], $match)){
            return $this->compute($match[0]);
        }

        return 0;
    }
}

test.php

<?php
require "Field_calculate.php";

$calc = new Field_calculate();

$tests = [
	[
		'expr' => '3/18-1/2 * 40',
		'res' => -19.8333333
	],
	[
		'expr' => '13/18 * 40',
		'res' => 28.88888888
	],
	[
		'expr' => '14 3/16/ 21 * 40',
		'res' => false
	],
	[
		'expr' => '16 3/16/ 23 * 40',
		'res' => false
	],
	[
		'expr' => '16-3/16 / 30 * 60',
		'res' => 15.625
	],
	[
		'expr' => '9.75 * 21.5/29.5',
		'res' => 710.593220339
	],
	[
		'expr' => '1/4 * 5',
		'res' => 1.25
	],
	[
		'expr' => '1/2 * 6',
		'res' => 3
	],
	[
		'expr' => '7 * 60',
		'res' => 420
	],
	[
		'expr' => '8 Ga. x 4',
		'res' => 32
	],
	[
		'expr' => '22 x 36',
		'res' => 792
	],
	[
		'expr' => '35/64 * 6',
		'res' => 3.28125
	],
	[
		'expr' => '100 -10',
		'res' => 90
	],
	[
		'expr' => '100 - 10',
		'res' => 90
	]

];

foreach($tests as $test){
	$res = $calc->calculate($test['expr']);
	echo "Expression: {$test['expr']}".PHP_EOL;
	echo "Expected:   {$test['res']}".PHP_EOL;
	echo 'Calculated: '.$res.PHP_EOL;
	echo 'Test '.(($res == $test['res']) ? 'passed' : 'failed');
	echo PHP_EOL;
	echo '------------------------'.PHP_EOL;
}

hi @DBX12,

Field_calculate's really helpful.
But look like $input = preg_replace('[^0-9\.\+\-\*\/\(\)]', '', $input); not work well to remove space in my case;

$formula = '100 -10'; // or '100 -  10'
$result = (new Field_calculate)->calculate($formula); // return 0

Hey @hoanganh25991,
thanks for the feedback. I'm not the creator of the class, I just hacked a short test script for a StackOverflow user, who wanted to know if it can solve certain expressions (in fact, exactly the expressions in the $expressions array).
After updating the tests, I realized, the class does not behave as expected. As it was only a test for a SO user of a class provided by an internet stranger, I do not plan to fix it in the near future - sorry.
However help by PR (not sure, if it's supported for gists) is welcome.
Greetings,
DBX12

Field_calculate's is really helpful.
i have a problem in use it.
return "Function create_function() is deprecated" for me!!!