Atari 800 - Page 26

ffiffiffi
To
edit any line
of BASIC
code, use
the display control
keys described
in
Section 7. Position
the cursor overthe
characters
you
wish to change
and make
the corrections
within
a
logical
line.
When
the line is
correct,
press
GEIrm.
The ATART
800 will
substitute
the corrected line in
place
of
the original
one
in
RAM. To remove
a
whole
line,
type
its line
number
and
GEEE.
For
practice,
replace
the word
"Wizard"
in
Iine 10 with your
own name.
Be sure to make
your
changes in
the numbered line
10, not
the
line
displayed
after "run.,,
To
see the
program
that
is
currently stored in
RAM,
type:
LiEt
GE?IIIIIT
L i s'b
is
the command
that makes
the computer
display
your
BASIC
source
program.
Any
time
you
wish
to see
the
instructions
your
computer is following,
push:
fiirL
and
then type:
Li*t
EIEII
Note
that
you
may useff$[to interrupt
the computer even
if it is
busy running
a
program
or
calculating.
All
other
commands
must
be
given
only after
f[S[
is displayed.
Commands
may
be
typed in any
combination of upper
and lower
case Ietters
but
they
will
always
appear
in a listing
in
upper
case.
Now
add
to
your
program
by entering
these lines:
1O
FRIN'f
'hli;rilrcJy
ar.rJ
rior..t ;!wiilk$?'
@l
?O frrr.ut
A$
@l
30
If A$
*
"Yes"
then
Frint
"Your
r,rclgrsrrming
c:areer
has
iust
hesun.'l
Got"o
60
EEEII
40 If A*
='No'then
Frint
"Technolos:,t
rra$
PBss iJclu Ltlro
. .
'
l Goto
10
GlE?llilll
Press
f!@[t
only
where in-
dicated
and
don't leave
out
the
colon
(:)
near
the
end
of each
line.
BASIC
language
ignores
blank
spaces
unless
they
are in-
side
quotation
marks
so
you
can
leave
them
out when
you
need
to save
space.
However, put
them in
if
you
can so
your
listings
will
be easier for
people
to read.
60
F'rint
"Tlris
r,rograrr
has endedr'r
Gl!ilHn
Run
this
program
by
typing
tUrr
and
fftIilIn
,
then
answer
the
question
"Are
you
awake,,?
several
times.
Type
your
answer
after the ?
and then
push
@[l
. Try
responding
Yes:
yes;
no;
and maybe.
What happens
when
your
answer is neither
"Yes" or
"No"?
Right. The
program prints
the message in
Iine
60 and
then ends.
To
understand what
the computer is
doing,
get
a new listing
and,
examine
it line
by
line.
Line
10 has
the com-
mand PRINT
"something." This
something
which
you
put
between
the
quotatlon
marks is
called
a string
cons-
tant.
String means
a string
of letters,
numbers,
and/or
graphic
characters-constant
because
it will
remiin
the
same
every
time
you
run
this
program.
Line
20 has the command
INPUT
something.
This
means:
"Computer,
wait
until something
is
typed
on the
keyboard.
Show whatever is
typed on
the screen
and store
it in
a space in
RAM
memory
tibeted'A$.
When
GEED
is
pressed
go
on to
the
instruction
with
the next higher
line
number."
A$
(read
A
string) is
called
a
string
variable-a
string
of
letters,
numbers,
and/or
graphic
characters
which
will
be different
every
time
you
run
this
program.
Each
string variable
within
a single
program
must
have
a different
Iabel.
Many
labels
are
available in
BASIC
but, for now,
limit
yourself
to A$
throughZ$.