adding info to an array?

I have a for loop, and an if that checks something, and if true, it's supposed to add info to an array called $ra, but instead of adding it to the array it seems like it's overwriting it, currently I'm using $ra[$r] = "$r"; where $r is a number.. after the for } I put a print_r($ra); and it only prints the last thing that was added to the array. How do I solve this? Haven't used arrays much so I'm trying to learn, but it's not going very well :) Håkan