Radio Shack TRS-80

What?
A
number
times
its
reciprocal is
supposed
to equal
1
exactly.
So what gives?
You
have
discovered
the
Computer's
limit of
accuracy. Just
like a
calculator
(or a
person),
a
computer can
never
be
perfectly accurate
all the
time.
For short
arithmetic
expressions, the
TRS-80
is
accurate to
the fifth or
sixth
decimal
place. In longer,
more
complex
expressions,
a
minute
error in
the
sixth
place
can be
magnified to where
it
becomes
significant.
All pro-
grammers
have to
cope
with
this kind of
built-in
error.
We'll discuss
one way
of
handling it
in a
later
chapter.
Calculator Mode
for
Troubleshooting
Suppose a
program
isn't
giving you
the
answers
you
expect. How
can you
troubleshoot
the
program?
One
way is
to ask
the
Computer
to tell you
what it
knows
about
the
variables
used
in the
resident
program.
Example:
PRINT
X. The
Computer
will tell you
what the
present
value
of X is.
Another
thought:
Something is
stored
in every
memory
cell
{even if
YOU
have not put
anything
there).
Enter and
RUN this
instruction in
the calculator
mode:
Comdex
programs.
dpmmlndasyoit
get
into
more
v>-i-.-
::-'"
'.'"-'t'
'.'.."";
PRINT
A,B,C,D,E,F
T
G,H,I,J,K,L,M,N,0,P,Q,R
t
S,T,U,V,W,X,Y,Z
The
answers
depend
on
the
values last
given
those
variables
—
even
from
much
earlier pro-
grams.
If
you turned
off the
Computer
since last
using
some of
the
variables, the
numbers
stored in
those
locations
will be
completely
arbitrary
and
meaningless.
The
Memory
Command
Since
the
programs
you
write do occupy
space
in the
Computer's
memory,
and
program
size is
limited
to how
much
memory you
have purchased,
it may
be
important to
know how
much
memory
you
are
using for a
given
program.
That's
what
the
Memory Command
is
for.
The
least
amount
of
memory
available in
the TRS-80 is
4K. This
means there are
about
4,999
different
memory
locations to
store and
process your
programs.
(Actually,
4096.)
(If you
have
8K of
memory, the
number is
8192;
for
16K it is
16384.)
This
manual is
meant
to be
forth*
computer
»
operator
and
programmer,
so
we
are studiously
avoiding
computer
efeetronies
theory
—
^whea
possible.
Owners
interested
in
that
phase of
this
interesting
subject
are
referred to
their locaf
Radio Shack
store
for
books
which specifically
:
addressitJ
.
-;:
':':.:,'.
To
get some
idea
what
this means,
type:
NEW
PRINT
MEM
38