Atari 400 Basic Reference Manual

FOR (F.), TO,
STEP/NEXT (N.)
4
PROGRAM
STATEMENTS
This section explains the commands associated with loops, conditional and un-
conditional branches, error traps, and subroutines and their retrieval. It also ex-
plains the means of accessing data and the optional command used for defining
variables.
The following commands are described in this section:
FOR, TO, STEP/NEXT
GOSUB/RETURN
GOTO
IF/THEN
ON,GOSUB
ON,GOTO
POP
RESTORE
TRAP
Format: FOR avar = aexp1 TO aexp2 [STEP aexp3]
NEXT avar
Examples: FOR X = 1 TO 10
NEXT X
FOR Y = 10 TO 20 STEP 2
NEXT Y
FOR INDEX
= Z TO 100 * Z
NEXT INDEX
This command sets up a loop and determines how many times the loop is exe-
cuted. The loop variable (avar) is initialized to the value of aexp1. Each time the
NEXT avar statement is encountered, the loop variable is incremented by the
aexp3 in the STEP statement. The aexp3 can be positive or negative integers,
decimals, or fractional numbers. If there is no STEP aexp3 command, the loop
increments by one. When the loop completes the limit as defined by aexp2, it
stops and the program proceeds to the statement immediately following the
NEXT statement; it may be on the same line or on the next sequential line.
Loops can be nested, one within another. In this case, the innermost loop is com-
pleted before returning to the outer loop. The following example illustrates a
nested loop program.
10 FOF.: >=:= 1 TO 3
:::IJ PF.:HH
11
0UTER LOOP"
30 Z=f1
40 Z=Z+2
50
FOP
'·.1-i
1-1
6~3
PF.:It·H
II
7f1
t·~E>::T
'··'
I
:::0 t·4E>::T
>=:
90 am
TO
C" ,- ...... ~:, -,
·-' .:: I t.:- .::..
I Nt·iE~: LOOP n
Figure 4-1. Nested Loop Program
Program Statements 15

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)