CODEWITHSUNDEEP
phpregex
Chintan
Chintan

Reputation: 1204

Is there possible to check mathematical expression string?

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....

Upvotes: 2

Views: 2091

Answers (3)

Jendas
Jendas

Reputation: 3579

Well I suppose that the thing, you are looking for, is some Context-free grammar or Pushdown automaton. It can not be done only using regular expressions. (at least there is no easy or nice way)

That is because you are dealing with nested structures. Some idea of an implementation can be found here Regular expression to detect semi-colon terminated C++ for & while loops

Upvotes: 1

axel.michel
axel.michel

Reputation: 5764

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);
}

Upvotes: 2

Vimal Patel
Vimal Patel

Reputation: 607

Use Regular Expression that returns you howmany Opening Brackets and Closing Brackets are there?

then check for the number of both braces....if it is equal then your expression is right otherwise wrong...

Upvotes: -1

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