Atari 800 Basic Reference Manual

42 Array s and Matrices
A DIM statement is used to reserve a certain number oflocations in memory for
a string, array, or matrix. A character in a string takes one byte in memory and
a number in an array takes six bytes. The first example reserves 101 locations
for an array designated A. The second example reserves 7 rows by 4 columns
for a two-dimensional array (matrix) designated M. The third example reserves
20 bytes designated B$. All strings, arrays, and matrices must be dimen-
sioned. It is a good habit to put all DIM statements at the beginning of the pro-
gram. Notice in Figure 8-1 that although the array is dimensioned as DIM A(6),
there are actually 7 elements in the array because of the 0 element. Although
Figure 8-2 is dimensioned as DIM M(6,3), 28 locations are reserved.
Note: The ATARI Personal Computer does not automatically initialize array or
matrix variables to 0 at the start of program execution. To initialize array or
matrix elements to 0, use the following program steps:
250 orr·1 A( 100 >
300 FOR E==0 TO ll1l1
310 A(3 >=0
32f1 t·E·<T E
Arrays and matrices are "filled" with data by using FOR/NEXT statements,
READIDA T A statements and INPUT commands. Figure 8-3 illustrates the
"building" of part of an array using the FOR/NEXT loop and Figure 8-4 builds an
array using the READ/DATA statements.
10 DH1 A< we>
2f1 ::·::= 1 (1
3(1 FO~: E=1 TO 9(1
40 ::-::=:~ =:+ 1
50 A(E )=>=:
60 t· 4E>::T E
70 FOP E=1 TO 90
B(l PF.:H-JT E.. A( E >
90 t · ~E::-=:T E
Figure 8-3. Use of FOR/NEXT to Build An Array
10 DH1 A(3)
20 FOR E=l TO 3
30 F.:EAD >=:
40 A(E>=>=:
50 PRHiT A<E ).,
60 t·~E::- = :T E
70 am
10(1 DATA 33 .. 45 ., 12
Figure 8-4. Use of R.EAD / DATA to Build An Array

Atari 800 Specifications

General

Processor	MOS Technology 6502
Processor Speed	1.79 MHz
ROM	10 KB
Graphics	ANTIC and GTIA chips
Release Year	1979
Display Resolution	up to 320 x 192
Colors	128 colors
Sound	4 channels
Storage	Cartridge, cassette, floppy disk
Ports	Cartridge, serial, monitor
Operating System	Atari OS