Extract element from a logical expression in php

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Given a logical expression ( for eg. ((A AND B) OR C) ) , How can one extract individual elements like A, B, C in php. The logical expression can be anything , comprised of AND, OR and BRACKETS.
Thanks in advance.

Posted 24-Sep-13 22:06pm

mg9893

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Akinmade Bond 25-Sep-13 5:27am

Can you please be more explicit? You want to extract the variables from a logical expression?

mg9893 25-Sep-13 11:52am

Yes I want to extract variables from any logical expression given by the user.

Akinmade Bond 25-Sep-13 12:39pm

The user is supposed to write the logical expression?

mg9893 25-Sep-13 12:48pm

Yes,Its a part of a project. I am taking a logical expression comprised of AND, OR , BRACKETS and VARIABLES from the user as an input , then after extracting variables , I am working on those individual variables.

Akinmade Bond 25-Sep-13 12:58pm

You could filter the user input, stripping out logical variables and special characters.

mg9893 25-Sep-13 13:15pm

I'm new to php thus not getting how to do this. suppose user inputs
If (animal flies) AND (animal lays eggs) then (animal is a bird). I want to extract animal flies , animal lays eggs and animal is a bird.

Akinmade Bond 25-Sep-13 13:36pm

See my answer, not perfect yet. It relies on the fact that variables do not contain spaces.

mg9893 25-Sep-13 13:59pm

Got it. Thank you.

Akinmade Bond 25-Sep-13 17:37pm

Happy to help.

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Akinmade Bond · Answer 1 · 2013-09-25T07:35:00

Try this, you should be able to improve on it.

PHP

if (!empty($_POST)) {	
	//The list of words to remove
	$keywords = array( 'IF', 'THEN', 'ELSE', 'ENDIF', 'AND', 'OR', 'XOR', '&&', '&', 'IS', 'NOT', 'WHERE' );
	//The expression the user entered.
	$logic =  explode(' ', htmlentities ( strtoupper( trim($_POST['logic']) ) )  ) ;
	//Remove all keywords and print them to screen.
	foreach (array_diff( $logic, $keywords ) as $key => $value ){
		echo $value .'<br />';
	}
}

?>

<form method="post">
<textarea name="logic"> </textarea>
<input type="submit" />
</form>