If statement check if string is a question mark

I have been programming in PHP since almost 15 years, and today I am asking a simple question that is puzzeling me. I need to check if the string is a "?"... but it does not work.

$niveau = 0;
$result = "Original";
if($niveau == "?") $result = "Found a question";
echo "Result :".$result;

Output: Result : Found a question

Question, since the value of $niveau is 0, the if statement should not change the value of $retour, but it DOES! Why? Can somebody explain this behaviour?