Question

I want to check all brackets start and close properly and also check it is mathematical expression or not in given string.

ex :

$str1 = "(A1+A2*A3)+A5+(B3^B5)*(C1*((A3/C2)+(B2+C1)))"

$str2 = "(A1+A2*A3)+A5)*C1+(B3^B5*(C1*((A3/C2)+(B2+C1)))"

$str3 = "(A1+A2*A3)+A5++(B2+C1)))"

$str4 = "(A1+A2*A3)+A5+(B3^B5)*(C1*(A3/C2)+(B2+C1))"

In above Example $str1 and $str4 are valid string….

Please Help….

Answer 1

You’ll need a kind of parser. I don’t think you can handle this by a regular expression, because you have to check the amount and the order of parentheses and possible nested ones. This class below is quick PHP port of a Python based Math expression syntax validator of parentheses I found:

class MathExpression {

    private static $parentheses_open = array('(', '{', '[');
    private static $parentheses_close = array(')', '}', ']');

    protected static function getParenthesesType( $c ) {
        if(in_array($c,MathExpression::$parentheses_open)) {
            return array_search($c, MathExpression::$parentheses_open);
        } elseif(in_array($c,MathExpression::$parentheses_close)) {
            return array_search($c, MathExpression::$parentheses_close);
        } else {
            return false;
        }
    }

    public static function validate( $expression ) {
        $size = strlen( $expression );
        $tmp = array();
        for ($i=0; $i<$size; $i++) {
            if(in_array($expression[$i],MathExpression::$parentheses_open)) {
                $tmp[] = $expression[$i];
            } elseif(in_array($expression[$i],MathExpression::$parentheses_close)) {
                if (count($tmp) == 0 ) {
                    return false;
                }
                if(MathExpression::getParenthesesType(array_pop($tmp)) 
                    != MathExpression::getParenthesesType($expression[$i])) {
                    return false;
                }
            }
        }
        if (count($tmp) == 0 ) {
            return true;
        } else {
            return false;
        }
    }
}

//Mathematical expressions to validate
$tests = array(
    '(A1+A2*A3)+A5+(B3^B5)*(C1*((A3/C2)+(B2+C1)))',
    '(A1+A2*A3)+A5)*C1+(B3^B5*(C1*((A3/C2)+(B2+C1)))',
    '(A1+A2*A3)+A5++(B2+C1)))',
    '(A1+A2*A3)+A5+(B3^B5)*(C1*(A3/C2)+(B2+C1))'
);

// running the tests...
foreach($tests as $test) {
    $isValid = MathExpression::validate( $test );
    echo 'test of: '. $test .'<br>';
    var_dump($isValid);
}