Atari 800 User Manual

Introduction to Atari BASIC 49
Before a string variable can be used in a program , it must first be
dimensioned with the DIM state ment. If a string variable is not
dimensioned before it is used in a program, the error 9 will occur.
A
string variable is dimensioned by giving its name and its
maximum size after the reserved word DIM . The maximum size
must be enclosed in parentheses. The
following DIM statement,
100 DIM A$(5)
dimensions a five character string. More than one string variable
can be
dimen s ioned in a single DIM statement. For example, the
following DIM statement,
100 DIM A$(10), B$(5), C$(7)
would dimension 3 string variables.
Tables & Arrays
Earlier in thi s chapter, we introduced the concept of variables. A
variable
is designed to hold a single data item--either string or
numeric. However , some programs req uire that hundreds or
even thousands of variable names be used.
Obviously, the use of thousands of individual variable names
could prove extremely cumbersome. To overcome this
problem , BASIC allows the use of subscripted variables.
Subscripted variables are identified with a subscript, a number
appearing within parentheses immediately after the variable
name . An example of a group of subscripted variables is given
below:
A(O), A(l), A(2), A(3), A(4), ... , A(100)
Note that each subscripted variable is a unique variable. In other
words, A(O) differs from A(l), A(2), A(3), A(4), etc.
Subscripted variables
should be visualized as an array (or table).
In our previous example, the data contained in the array defined
by A would consist of one row with 101 columns in it. Such an
array
is a single-dimension 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