Initializing The Arrays With Values?

I'm using a structure to hold three arrays:

structure myStruct
dim arrayOne() as char
dim arrayTwo() as char
dim arrayThree() as char
end structure

But how do I go about setting them a value, I've got my instance of myStruct

dim aStruct as new myStruct()

If I try redim, it just tells me it can't change the dimensions of an array, so how do I got about initializing the arrays with values?