Arrays

[Walt Decker]

I'm a little confused about what is going on with arrays.

If I:

DIM Array(20, 20)

"Array" should be from 0 to 19, 0 to 19. Is that correct?

However;

DIM Array(20, 20)

FOR I = 0 TO 20
    FOR J = 0 TO 20
       Array(I, J) = 2
    NEXT J
NEXT I

I am actually doing each loop 21 times and no runtime error is generated. Why?

[Steve Rossell]

I'm a little confused about what is going on with arrays.

If I:

DIM Array(20, 20)

"Array" should be from 0 to 19, 0 to 19. Is that correct?

However;

DIM Array(20, 20)

FOR I = 0 TO 20
    FOR J = 0 TO 20
       Array(I, J) = 2
    NEXT J
NEXT I

I am actually doing each loop 21 times and no runtime error is generated. Why?

No,

DIM Array(20,20)

is the same as doing

DIM Array(0 to 20, 0 to 20)

[Walt Decker]

Thanks, Steve. That's different from what I learned years ago with other basics.

[Cliff Nichols]

It depends on zer0 based vs 1 based
for details....as the rules depend on the application

Generically though

DIM Array(20, 20)

would result in an array with 21 elements (1 to 20 based), but each element starts from a number one less than the count

[Chris Holbrook]

It's not a bad discipline to use the full syntax when dimensioning arrays, for example, DIM SDFGHJKL(0 to 99).

Regarding multidimensional arrays, for some reason I find it more natural to use a single dimension and multiply out the index. No idea what impact this has on performance, but it keeps my code looking simpler.

[John Gleason]

...No idea what impact this has on performance, but it keeps my code looking simpler.

Every test I've done shows it's faster too, in certain circumstances maybe even approaching 2x.

DIM Array(20, 20)...would result in an array with 21 elements (1 to 20 based), but each element starts from a number one less than the count

1 to 20 there gives only 20 elements, did you mean 1 to 21, based on "one less than the count" logic?

[Cliff Nichols]

Yes I did John, I just mis-spoke what I meant

[Michael Mattias]

>That's different from what I learned years ago with other basics

Which BASICs were those? I can't remember any BASIC which did NOT use 0-based subscripts by default.

MCM