How to check specific words in a textarea?

[Marco Langes]

Hello,
first of all: Excuse me for some bad English you might experience during the reading of this.

So I made this form with an textarea, people can write a comment in here but I wanted to create something that my function counts specific words in it and says:
Word 1: 12 times
Word 2: 3 times
etc
etc

Code of what I have so far (I'm still a beginner in PHP):

$commentaar = trim($_POST['commentaar']);

function commenteva($commentaar)
	{
		global $commentaar;
		$commentaar = nl2br($commentaar); //newlines	
		
		$positive = array("goed", "top", "beste"); //Positive words
		$negative = array("slecht", "kut", "beter", "zuigt", "haat"); //Negative words
		
		$plengte = strlen($positief);
		$nlengte = strlen($negatief);
		
		echo ("<br />Aantal positieve woorden: " . $plengte);
		echo ("<br />Aantal negatieve woorden: " . $nlengte);
		
			if($plengte > $nlengte)
			{
				echo("<br />Commentaar is positief");
			}
			elseif($nlengte > $plengte)
			{
				echo("<br />commentaar is negatief");
			}
			else
			{
			echo("<br />commentaar is neutraal");
			}
	}

I just can't get it to work, each try I get different errors, I hope I am clear enough.

Thanks

[JKing]

Have a look at this function.
PHP preg_match_all( )

It checks for a pattern inside a string and returns the number of matches.