Dynamically referencing objects

I was wondering if anyone could help me with this simple problem:

The problem is referencing object names dynamically in AS3, eg in a loop

I have an array called c4 which i would like to reference like this

I have a number
var x:Number = 4

How can I do something like

(i know this is wrong!)

Same with other objects
eg. Movieclip called mc4

[“mc”+x].x = 100;

Thanks a lot for any help