declaring array of an object X with unknown size objective c

Question

How would I go about declaring an array in the .h file of an unknown size that I will calculate say in the a function inside the class ?

For example, I might have 20 or

Answer 1

Like rmaddy says, you can just allocate the array with malloc:

arrays_of_unknown_size= (NSArray**)malloc(N*sizeof(NSArray*));

You can also reallocate it with realloc, and the size may change.
Another way is to use an array containing an array:

NSMutableArray* array_of_unknown_size=[[NSMutableArray alloc]init];

Then when the array is already populated, get the single array that you want:

NSArray* myArray=[array_of_unknown_size objectAtIndex: myIndex];

Of course arrays_of_unknown_size is too long, don't use this name, it's just an example.