error: array subscript is not an integer

[Manal Helal]

Hi

I am trying to construct a multidimensional array (as linear array in
memory, but indexed with equations to represent the dimensions) of
size 30 each, and 6 dimensions, which is 30^6=729000000

using a long type for the array crashes, as it is outside the range
values. I used double long data type, and I had the above error: array
subscript is not an integer

Is there a work around this problem that I can implement,  or another
way of creating similar arrays?

I appreciate your help a lot,

Kind Regards,

Manal