Radio Shack TRS-80 User Manual page 69

Nothing
to
it!
A
was
printed 5 times and
B
printed
20
times.
If
you
are
having trouble
counting A's
and
B's
as
they whiz
by,
you remember what
to do. Just press the
(+), (+)
or
(*•)
key
to stop
execution and temporarily
freeze the display.
The
I
BREAK) key and
typing
CONT
do
the
same
thing, allowing hands-off
freezing,
but
inserts a
BREAK
note and other-
wise messes up
the display.
How
to
goof-up nested
FOR-NEXT
loops
The most
common
error
beginning programmers
make
with nested
loops
is
improper
nest-
ing.
Change
these
lines:
50
NEXT
A
60 NEXT B
...
and
RUN.
The Computer
says:
WHAT?
60
NEXT B?
Looking
at
the program
we
quickly
see that the
B
loop
is
not nested
within the
A
loop.
We
have
the
FOR
part
of the
B
loop
inside the
A
loop,
but the
NEXT
part
is
outside
it.
This
does not work.
A
later
chapter deals with something
called
"flow
charting",
a
means
of
helping us plan programs and
avoid
this
type of problem. Meanwhile
we
just have
to
be
careful.
Breaking out of
Loops
Improper
nesting
is
illegal,
but breaking out of
a
loop
when
a desired condition has been
met
is
OK, Add
these
lines:
50
NEXT
B
55
IF
A =
2
GOTO 100
60
NEXT
A
99
END
100
PRINT "A EQUALLED
2.
RUN
ENDED."
...
and
RUN.
67