Is string a math expression?

Question

How can I found if string is a math expression or not?

It is enough to understand basic math expressions +, -, x, /

For Example:

"1+1" => TRUE

"2 / 2" => TRUE

"hello" => FALSE

"1 * 2 - X" => FALSE

"me + u" => FALSE

check this http://stackoverflow.com/questions/9824552/how-to-determine-if-a-string-is-a-mathematical-statement-in-php — Dhiraj, Mar 17 '15 at 18:03
@Ferid: You want to know if a string contains a math expression and if it contains a string/integer? — Funk Forty Niner, Mar 17 '15 at 18:05
Lex it as a series of minimum-one digits split by exactly-one operator token. — kojiro, Mar 17 '15 at 18:15

score 1 · Answer 1 · edited May 23 '17 at 12:28

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);
}

you can check and read in detail about the solution here Is there possible to check mathematical expression string?

See also eval. For example, you can do this:

$result = INF;
try { 
  eval("$result=" + myMathExpression);  // Evaluate here
} catch (Exception $e) { 

} 
if($result != INF) echo("Expression is a valid mathematical expression.");

read more about it there

**Woah there!** From the [PHP manual page for `eval()`](http://php.net/eval): "The eval() language construct is very dangerous because it allows execution of arbitrary PHP code. Its use thus is discouraged. If you have carefully verified that there is no other option than to use this construct, pay special attention not to pass any user provided data into it without properly validating it beforehand." — esqew, Mar 17 '15 at 19:19
@esqew yes it is, that's why i put it on the second option. you may go with first one :) — Tashen Jazbi, Mar 17 '15 at 19:33

Serj · Answer 2 · 2015-03-17T18:46:34.087

0

An extremely simple solution: Regex number,whitespace,[+,/,*,-,=],whitespace,Substring(recursion here) will work for any sequence of 1 + 1 + 2 + ... + 1 = 2 + 3 + 4 = 1 * 4 ... etc.

Obviously would not check if an expression is legit.

As per request, pseudo code:

if  Regex(^(([0-9]+)(\s*)([+,/,*,-,=])(\s*)([0-9]+)(\s*)([+,/,*,-,=])(\s*)))
    if (recursion())
         return True;
    else
         return False;
else //checking for end point
    if Regex(^(([0-9]+)(\s*)([+,/,*,-,=])(\s*)([0-9]+)))
         return True;
    else
         return False;

edited Mar 17 '15 at 18:46

answered Mar 17 '15 at 18:07

Serj

26
4

It's just a scratch of good answer. @Serj, can you provide actual regex? – Paweł Tomkiel Mar 17 '15 at 18:12
It's not for _my_ enjoyment, but for the quality of answers on **SO**. Taking back that downvote for your effort. – Paweł Tomkiel Mar 17 '15 at 19:34

Christophe Maggi · Answer 3 · 2015-03-17T18:08:33.250

-1

Maybe a regex with a pattern like this :

^([-+/*]\d+(\.\d+)?)*

edited Mar 17 '15 at 18:08

answered Mar 17 '15 at 18:06

Christophe Maggi

132
6

Is string a math expression?

3 Answers3