gorillamath,
You do not have to declare a length in all cases - but there are 2 types of data collection variables in AutoIt - arrays and maps - which both use very similar notation. It is the manner in which the variable is declared which determines its type:
Local $aVar[3] ; An Array
Local $vVar[3] = [1, 2, 3] ; An Array )
Local $vVar[] = [1, 2, 3] ; An Array ) These 3 declarations are functionally identical
Local $vVar = [1, 2, 3] ; An Array )
Local $mVar[] ; A Map
So as you can see, there is no need to declare the size of an array if you declare the content at the same time. Declaring neither size nor content creates a map.
Does that help?
M23