Atari 400 User Manual

68 User's Handbook to the Atari 400/ 800 Computers
loops is to end an outer loop before an inner loop is ended. Also,
be certain that that every NEXT statement has a matching FOR
statement. If the Atari BASIC int erpreter cannot match every
NEXT statement with a preceding FOR statement, an error will
result.
Conditional Statements
One of the most important features of a computer is its ability to
make a decision. BASIC uses the IF, THEN, ELSE statement to take
advantage
of the computer's decision making ability. The IF ,
THEN,
ELSE statement takes the following form:
IF expression THEN statement ELSE statement
The IF statement sets up a question or a condition. If the answer
to that question is true, the statement following THEN is
executed. If the answer is false, the statement following ELSE will
be executed.
In the following example, if X is equal to 0, then Y will be set to 1.
If X is not equal to 0, Y will be set to O.
100 IF X = 0 THEN Y = 1 ELSE Y = 0
The IF, THEN, ELSE statement may be shortened to just IF, THEN
as shown below.
050 Y = 0
100 IF X = 1 THEN Y = 1
In this example, if X is equal to 1, the statement following THEN
will be executed . If X is not equal to 1, program execut ion will
continue with the next program statement (in our examp le--line
200).
Branching Statements
Branching statements change the execution pattern of programs
from their usual line by line execution in ascending line number
order. A branching statement allows program control to be

Atari 400 Specifications

General

Manufacturer	Atari
Model	400
Type	Home Computer
Release Year	1979
CPU	MOS Technology 6502
CPU Speed	1.79 MHz
ROM	10 KB
Operating System	Atari OS
Keyboard	Membrane keyboard
RAM	8 KB (expandable to 48 KB)
Graphics	ANTIC and GTIA chips
Sound	4 channels
Display	RF output for connection to TV
Storage	Optional cassette tape drive or floppy disk drive
Ports	Cartridge
Display Resolution	320x192 (16 colors)