Radio Shack TRS-80 User Manual page 55

Chapter 11
Son
of
FOR-NEXT
This
is
heady
stuff. If
you
turned
off the
Computer between
Chapters, load the
program
which you
taped
from Chapter
10 into the
Computer.
Modify
the
program so the
rate
and time
are calculated
and printed for every
50
mph
incre-
ment
instead
of the 100
mph
increment
presently
in
the program,
RUN.
Answer: 80
FOR
R =
200 TO 1000 STEP 50
Trouble
in the
Old
Corral
What
a revolting
development!
The
printout goes so
fast
we
can't
read
it,
and by
the time
it
stops, the top part
is
cut
off.
Aught
'a
known
you
can't trust these computers.'
Solutions
For
Sale
Several solutions are available:
1.
Pressing nearly
any key
will
stop
program
execution.
Try RLJNning
a
number
of times,
pressing different
keys (and the space
bar)
during the
run, to see
what
happens.
RUN
again, this
time
using only the + (up-arrow), to freeze the display. Nifty
—
huh?
Clean stop
—
clean
restart.
This
is
the
key
to use for
temporary
freezes.
2. If
you want
a classy display
you
can
build a
"pause"
into the
program.
The
screen
will
fill,
halt a
moment,
and automatically go on
if
you
don't interrupt the program.
The
Timing
Loop
In
order to learn about the timer
loop,
let's
employ
another
sly trick.
We're going
to leave
our "Flight
time" program
in the
Computer, and put
in
a
second program.
As-.
you can
see, pressing
a ksy not only stops execu-
tion
but
inserts
its
own
letter
of number. Messy!
i-
"ii"
There's-
ffppthe* one:
y
ou
em
try
—
but
it'&not.a
vswry useful
oae
;
press [break;
key. That's
even
jjiessier
than the
fitst
one.
(To
restart after a
[break]
,
either enter
RUN
to start
program
ail
over again or
C
ON
T
-to
continue execution
*t
..
;-.
ther
"break-point
,f
)
53