Commodore 16 User Manual
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BRIEF INTERLUDE: You can
lype
tellers,
numbers
and
punctuation
rn
reversed print. Reverse letters make
excellent
headlines.
You can
also
use ihem (o
hignltght
special words and numbers. You can
type
graphic symbols in reverse
for the same effect To
put a
racing
stripe on
your screen,
select
a colour you like and
type
(he symbol
—
fby
pressing
s&FT
and
E)
across an
entire line. Then turn on
reverse
printing; fill the next line with the same-symbol. only
reversed.
On Ihe next line, type
SHIFT
and R (still in reversed print).
Then turn off
reverse, and fill (he last
line
with iuft and R (no
longer reversed).
Now your screen has a racing
stripe
In whatever
colour
you chose;
perhaps it is
a humble achervement, but it does
give your screen
a
certain flair .
. .
THE FIRST
STEP
What is a program, anyway? An experienced programmer
might tell
you that a program is a series of ordered statements organised
to
direcl
the computer
to
perform
a sequence of steps toward some purposeful
result What
you
may
learn
from this
is not to ask an experienced
programmer
what a program is.
The following, although
it is only two lines long, qualifies
as a
program.
Type it exactly
as
it
appears here. Don't leave
out the
numbers
at the
beginning
ot each line, since
they are the line numbers; they tell your
computer
what order
to
read
and
perform
the lines of the program.
Be
sure to press the
return
key
at the end of
each tine you type.
10 PRINT'FIRST
TRY"
20 GOTO
10
HUN
This line tells
your computer
to
print the
words FIRST TRY on
your screen
This line tells your
computer to go back to
line 1 and print FIRST TRY again.
When
you type
this and presb return
your computer does what each line tells it to
do.
Press
the run/stop Key to
slop Ihe
program.
Why did your computer print FIRST TRY
so many
times?
PRINT Is a
command mat tells your computer
to
PRINT what appears between
the
quote
marks
on the screen. When your computer reads this line, it
44
1
I
r f
I i
!
f
i
i
r i
!
i
(
I
I
1
I
I I
I
I
'
i
r
i
i
i
i
(
(
i
(
i
r
i
r
i
i
f
i
i
t
[
i
executes (carries
out) that command. GOTO tells your computer
to go
back
lo
line 10
and execute the
command
(PRINT "FIRST TRY") Each
time your computer
got
to line
20.
It executed the GOTO command,
returning to
line
10 again and again This repetition is called
a
loop.
The run/stop key breaks into whatever program the computer is
running,
and returns control of the keyboard back to you.
TIP:
Want lo
slow
down
this program
(or
any olher) without
slopping
it? Just hold down the
©
key
Now
type Ihe
following, pressing return after
each
eniry.
NEW
This tells
the
computer
to
forget
the last program
and get
ready
for
a
new
one.
The computer responds with the message
READY
You don't type this; this is your
computer letting you
know
that
It's
READY tor new commands or
programs.
10 PRINT
*
o
COMMODORE
I
16"
Press
CfBt and Bvson
Press and Rvs off
Notice
whal happens when you typo RTS ON and IVS OFF inside the
quote marks. They appear
on the
screen
as reversed
characters.
Now
type RUN and pres; return
lo see Ihe program.
When
the
program
is
RUN, your
Commodore
16 reads these reverse characters
as
what
you typed In,
and carries
out Ihe reverse print
as
instructed The same
principle holds true
(a
reversed character appearing
on
the screen
as a
representation for wnat you type) for doing other things in
a
PRINT
statement,
like
moving the cursor and changing colours, when
you
RUN
a program.
45