Atari 800

LEARN
TO
PROCRAM?
,m
WHY
You may f
ind
that there
are
no
preprogrammed
car-
tridges
or cassettes
which
make the computer
do
exactly
what
you
want. Or,
you
may decide that
learning to
program
is an
important
part
of
your
career or
educational
plan.
Even if
you
have no
practical
use
for computer
programming
you
will
f ind that
learning to
write
programs
in BASIC
for
your
ATARI 800
is an ex-
citing
and
valuable experience.
Programming
sharpens
your
skill
in thinking-
in
analyzing
pro-
blems
and devising
step-by-step
solutions.
lt
deepens
your
understanding
of computers
in
general,
and no one
can deny
that computers
are
becoming
a
major force
in modern society.
A
know-
ledge of
programming
makes
you
a more
informed
consumer
and
citizen
who no
longer accepts "it
was the computer's
fault" as an
excuse
for bad
management.
But
perhaps
the
most important
reason to
learn to
program
is
that
it is
fun.
Start
by
instructing the
computer to
draw
pictures
and to
print
verbal
messages
on the
display screen. Soon
you
will be
choosing
more and
more complex
tasks
for
your
ATARI 800 and
will be enjoying
the challenge
of
designing
programs
"which
allow the computer
to
do
your
bidding.
Cood
computer
programs
are usually created
in
three stages
-
design,
coding and
debugging.
During
design
you
choose
a task
for the computer
and
analyze
it into
component
parts.
During
coding
you
translate
these
parts
f rom
their
English or
mathe-
matical form
into a computer
language,
in
this
case
Atari BASIC.
You
type
your
coded
program
into the
ATARI 800 Computer.
As
each
line
is
typed
Atari
BASIC
will
check
it
and
report any
mistakes
in
coding.
After
you
have
corrected
these
mistakes
you
can try to
RUN
your
program.
That
is,
you
direct the computer
to
follow the
set of
instruc-
tions
you
have
given
it.
Often
you
find
you
have
made other errors. Sometimes
the
ATARI 800 may
succeed
in running
your program,
yet
the
result is
not exactly what
you
intended.
You
have made an
error
in
design
and need to
go
back
and
plan your
program
more carefully.
At other times
the com-
puter
will
tell
you
that
it can't
follow
your
instruc-
tions as
given
because they
contain
logical or
gram-
matical errors.
You have
made a second
stage error
in coding or typing.
At
the
third stage-debugg-
ing-
you
f ind and correct
all of
your
remaining
er-
rors. You continue
to run and
debug
your
program
until the
ATARI 800, under
the control
of
your
pro-
gram, produces
the
results
you
desire.
Note that no computer
actually
"solves
problems"
or
"answers
questions."
Using
your
design,
the
computer
performs
the
instructions
you
have
given
it.
lt mechanically
produces
your "solution"
to a
problem
or
repeats
your "answers"
whenever
you
run the
program.
BASIC
(Beginners
All-Purpose Symbolic
lnstruction
Code)
was invented
so that
people
could
Iearn to
write
programs
quickly
and easily.
To
you,
the user,
the
BASIC language
is a set of
rules
which tellyou
how to
give
the computer
the
instructions
it needs
to
do
your
bidding.
To
the
computer,
BASIC
is
the
same set of
rules
written in
machine
language.
They allow
it
to translate
your
BASIC
instructions
into
action.
We call this
machine language
pro-
gram
the
BASIC
Language
lnterpreter.
lt is
contain-
ed
in
the
Atari BASIC
l.anguage Cartridge.
The
pro-
gram
which
you
write
is
called
the
BAS/C Source
Program. You enter
your
source
program
into the
ATARI
800 RAM
memory by typing
it on the
keyboard with the
BASIC Cartridge
in
the
left car-
tridge
slot.
The ATARI
800 uses the Operating
System
Programs
(in
the Operating
System
ROM),
the
BASIC Language
lnterpreter
(in
the cartridge)
and
your
BASIC source
program
(typed
on the
key-
board or
loaded
from
cassette
or
disk and
stored
in
RAM memory) to
enable
it
to
follow
your
instruc-
tions.
3