Radio Shack TRS-80 User Manual page 50

We now
have a
program with
two controlled loops,
sometimes
called
DO
loops.
The
first
do-loop
DOES
something
five
times;
the second
one
does
something three times.
We
used
the
letter
N
for
the
first
loop
and
M
for
the second, but
any
letters
can be used. In
fact,
since
the
two loops
are totally separate
we could have used the
letter
N
for
both
of
them
-
not an
uncommon
practice in
large
programs where
most
of the letters
are
needed
as
variables.
RUN
the
program, being sure
you understand the
fundamental principles
and the
varia-
tions
we
have
introduced.
From>to Incrementing
There
is
nothing magic about the
FOR-NEXT
loop, in fact,
you
may
have already
thought
of
another (longer)
way
to
accomplish the
same thing
by using features
we
learned earlier.
Stop
now, and
see
if
you
can figure
out
a
way
to construct a
workable do-loop substituting
something
else in
place of
FOR
and
NEXT.
Answer:
8
N =
1
10
PRINT "HELP
MY
COMPUTER
HAS GONE
BERSERK!"
15 N = N +
1
20 IF
N<6
THEN
10
30
PRINT
"NO
IT'S
UNDER CONTROL
.
"
We
say that line
8
initializes
the value of
N, giving
it
an
initial
or
beginning value of
1.
Be-
fore initializing
to the value
we
want,
N could have been any
number
left
over
from
a pre-
vious
program.
Line
15
then increments
it
by
1,
making
N
one
more
than
whatever
it
was
before.
Line 10
uses
one of
our
relational
operators,<, to see
that the
new
value
of
N
is
within the
bounds
we
have established. If
not, the test fails
and
the
program continues.
48
Initializes
—
initially,
or
at
the beginning, sets the
value of
one of our
variables
{
or
starts
a program
baek atthe beginning).
Increments
—
steps (Increases
or decreases values
in specific stepsi
by
%%
3%
:
5 V,'
or
whatever).
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