Atari 800 User Manual

128 User's Handbook to the Atari 400/ 800 Computers
30 (X<100) is true. As a result, the statements after THEN are
executed, and the values
of X and Yare printed.
The following example illustrates the use of algebraic
expressions. An algebraic expression is true when it does not
equal zero.
EXAMPLE
10 FOR I =-2TO 2
20 IF NOT I THEN END
30 PRINT I
40 NEXT I
RUN
-2
-1
The previous example contains a
program that ends when a
condition is true. The condition is NOT I. NOT I is true when I is
false, and I is false when I is set equal to zero. When I has any
value
other than zero, it is true.
Line
10 begins a FOR / NEXT loop. The first time the loop is
executed, I is set equal to -2. Line 20 is an IF / THEN statement
with the condition NOT I. When I is set equal to -2, it is
considered true because it is not equal to zero. Since I is true,
NOT I is false.
The
condition at line 20 is false, so the program does not end.
Line
30 is executed next, so the value of I is printed. Line 40
returns the program to line 10 , where the counter (I) is
incremented by 1. I is set equal to -1 , so I is still true. Since I is
true, NOT I is false. The condition of line 20 fails, so the value of I
is printed.
When the loop is ex ecuted the third time, I is set equal to zero. I
is false, so NOT I is true. Since NOT I is true , the program is ended
at line 20.

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