Radio Shack TRS-80 User Manual page 73

It
has
nothing to
do with
the
INT
function.
Back
in
Chapter
8
we
talked a
little
about
the
Computer's accuracy (you always have to
watch
the accuracy
of
the
last
decimal place
or two).
TRS-80
users
who
have
LEVEL
II
Basic
will
not notice
this
routine "rounding
error". If
we
solved
all
the world's
problems
with the bottom-of-the-line
machine you
might not want
to
upgrade
to the higher
power
models, and one
doesn't stay
in
business
long
that
way, does one?
There
is
a
way
to control the accuracy of
your
results in
LEVEL
I
BASIC.
It
involves
artificially
rounding your
fraction to the desired
number
of decimal
places,
and then
forc-
ing the
Computer
to print
out only those
digits
which
are
"properly rounded".
For example, suppose
you
only need n to three places. (Of
course,
you
can enter
it
as
3.142,
but
that's
not
the point.)
Type
NEW
,
then enter and
RUN
the following program:
10
X=3 .14159
20
X=X+.0005
30
X=INT{X*1000>/1000
40
PRINT
X
Try
using other values for
X
(just
make
sure
X*1000
isn't
too
large for the
INT
function to
handle).
It's
easy to
change the program
to
accomplish rounding
at a different point.
For example,
to round
X
off
at
the hundredths
-place (2 digits to
the
right
of the decimal
point),
change
lines
20 and 30
to read:
20
X=X+.005
30
X=INT(X*100 J/100
and
RUN,
using several values for X.
HmmmmH!
Do you
suppose
there
is
any way
to separate each of the
digits in
3,14159, or in
any other
number?
Do
you
suppose
we would
have brought
it
up
if
there wasn't? After
all
. . .
(mum-
ble,
mumble
.
,
.).
It's
really
your turn
to
do some
creative
thinking, but
we'll get
you
started
and
see
if
you
can finish this idea. First,
wipe out the resident
program and
retype the
program
that
splits
X
into an integer
and fractional part (the first
program
in this
Chapter).
We
clearly can't just
go on
taking the
INT
value of
X
over
and
over to try
and
split
down
decimal
value. Let's try
it
with Z.
Adding
.0005 gives
our
fraction a "push
te
the
:
right
direction".
If this
fraction has
a digit greater
than
4
in its
10-th ousasdths-plaee, then
adding
.9995 will effectively
increase the thousandths-
place
digit
by
1.
Otherwise, the added .$$05
will
have
no
effect
on the Qnal
result.
This
results
m.\\---
what's
called
"4/5 rounding."
This
is
useful
when
you're printing
otlt
dollars-and-
cerits
—
1
t
pre ven
ts
$39.
99
5-ty
pe
prices.
71