PHP eval problems

I have variables $q1 - $q50. I want to loop through and see if they are set before I go on to the next bit of code. I am trying to use a for loop and eval. I think I am using eval incorrectly, probably because I am so used to actionscript. Can anyone take a loot at this for me and tell me what I’m doing wrong?

		$valid = TRUE; 
		$valid = FALSE; 
		echo "Please make sure all questions are answered.";