Atari 800 User Manual

76 User's Ha ndb ook to the Atari 400 / 800 Compute rs
String Handling
As a programmer, you will encou nter a numb er of situations
where you may need to wo rk w ith s trin g data. For examp l e, you
might want to comb ine severa l strings, compare t wo st rin gs,
sepa rate portions of a string, or even conve rt st ring data to its
numeric equi va lent. Atari BAS IC allows for a ll of the se.
Substrings
Atari BASIC allows the pro gra mmer to extract a portio n of a
string,
known as a substring. How eve r, Atari BAS IC accomp lish es
this extr action in a manner whi ch is very different fr om other
versions of BASIC, which u se MID$, RIGHT$, and LEFT$ to
accomp lish this task.
Atari
BASIC u ses the following configurat ion to extract a
substring.
NAME$ (first, last)
Where NAME$ is the name of the string from which the substring
is
to be extracted, fir st is the positi on of the first character from
NAME$ to be includ ed in the substrin g, and l as t is the positi on of
the l ast character from NAME$ to be in cluded in the substrin g.
For exampl e, if X$ consisted of the following ,
"JOHN JOH
NSON"
the s ub string defined by X$ (1,4) wou ld consi st of "JO HN ", and
X$ (6,12) wo uld consist of "JOHNSON". Notice that the blank
space in X$ is co unt ed as one character position.
The first and l ast character position in a s ub string spec ifi cation
can
be specifi ed with a variable or an ex pression as well as a
constant.
Also, the l ast character position need not be specified.
If it is not, the ent ir e right hand portion of the string will be
returned beginning with the specified first character.
Substrin
gs ca n be used to replace characters in larger strin gs. In

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