Atari XL User Manual

58
The Afar; XL Handbook
The characters in the middle of the string, which
have not been defined by any of your commands,
turn out to be hearts. The character code of a heart
is zero, and the memory is filled with zeros when
the Atari is switched on.
The facility to manipulate strings in this way and
the fact that a string may hold a very large number
of characters allows a single string variable to be
used in a similar fashion to a numeric array
variable. An "array" or ten strings, each with a
length of20 characters of less, can be fitted into one
string with a length of 200 characters by allowing
20 character positions for each of the substrings.
The substings can then be read and replaced using
the commands outlined above.
There are two problems in using strings like this.
The first is that the string is initially filled with
hearts. This can be overcome by filling the string
with spaces before adding any data to it:
10 DIM ARRAY$(200)
20 FOR Z=1 TO 200
30 ARRAY$(Z)=""
40 NEXT Z
The second problem is that every time new
material is inserted into a string, the position of the
end of the main string is reset to the position of the
end of the inserted portion. The answer to this is to
wri te a space in the last character space of the main
string after every modification:
150 ARRAY$(140)="NEW STUFF"
160 ARRAY$(200)=""
There are one or two other point to watch out for.
Garbage characters maybe left behind if you
replace an element with a shorter string. This
again can be solved by writing spaces into the

Atari XL Specifications

General

Release Year	1983
CPU	MOS Technology 6502C
Graphics	ANTIC, GTIA
Sound	POKEY (4 channels)
Storage	Cassette tape
Ports	Cartridge
Operating System	Atari BASIC
CPU Speed	1.79 MHz
RAM	64 KB