Radio Shack TRS-80 User Manual 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