Atari 400 User Manual

Intr od uct ion to Atari BASIC 71
The execution of subroutines is controlled by the COSUB and
RETURN statements. The format for the COSUB statement is as
follows.
COSUB
lin e numb er
The computer will begin execution of the s ubroutine beginning
at the lin e number indicated. Statements will continue to be
executed in
order, until a RETURN statement is encountered.
Upon execution of the RETURN statement, the computer will
branch out of the subroutine back to the first line following the
original COSUB statement. This is illustrated in the following
example.
Illustration 3-5. BASIC Program With a Subroutine
Subroutine
050 DIM ER$(50) , B$(50)
100 PRINT "ENTER CHECK AMOUNT"
200 INPUT A
300 COSUB 900
400 PRINT " ENTER PAYEE'S NAME"
500 INPUT B$
600 PRINT B$ , A
700 COTO 100
900 REM ERROR SUBROUTINE
910 ER$ = "NOT ALLOWED"
920 IF A < 0 THEN COTO 100
930 IF A>1000 THEN PRINT ER$
940 IF A = 0 THEN 999
950 RETURN
999 END
Subroutines can
help the programmer organize his program
more efficiently. Subroutines also can make writing a program
easier. By dividing a lengthy program into a number of smaller
subroutines, the complexity of the program will be reduced.
Individual subroutines are smaller and therefore more easily
written. Subroutines are also more easily debugged than a
longer program .

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)