Flash and the Three R's

Why is it that when i have my array of numbers, say

 nvalues = new array("5", "6", "7", "66");

and sort them…

 nvalues.sort();

and then trace the answer…

 trace(nvalues[0]+", "+nvalues[1]+", "+nvalues[2]+", "+nvalues[3]);

I get this:

5, 6, 66, 7

I thought it was fairly obvious that 66 is greater 7…

How do i fix this?!

Most irritated,

Len:(