Radio Shack TRS-80 - Page 160

CSAVE!
Before
going on to
the next section, you
may want to save the
square
root subroutine on a
cassette, to
avoid
the tedium
of
typing it in correctly
again
later.
You can save
all
the
sub-
routines
separately,
all
together, or
in various
combinations. This will let
you
load just the
ones you need
for
a
given
purpose.
From
Square Roots to
Circles (Well,
Ovals
Anyway!)
While you've got
the square root
subroutine
loaded,
we'll demonstrate how
scientific sub-
routines
can be put to
some
fairly
entertaining
uses. Type in the
following
program:
10
CLS
20
FOR
R
=
2
TO
22
STEP
4
30 FOR
A=-R
TO R
40
X=R*R-A*A
:
GOSUB
30030 !
Y=INT(Y-.5)
50 SET
(A+60.23+Y)
60 SET
( A+60.23-Y)
70
NEXT A
80
NEXT -R
90
GOTD
90
And
RUN.
If you
entered
the program
correctly,
the Computer
will
generate a series of
concentric
circles.
The program
uses the formula for
finding the coordinates
of
a circle on a graph:
Y
=
JR*R-X*X
(Y
is
the Y-coordinate, X is the
X-coordinate,
and R is
the radius.)
Use
[BREAK] to
get out
program.
Actually
they're ovals,
because
the
graphics
points
ate
rectangular
instead
at
square
—
it
would ta&e a
slightly
modified
program
to
generate
more
perfect
circles.
Care to try"?
158