Radio Shack TRS-80 User Manual page 139

100
P.AT20,"GR
APH
HEADING"
150
F.N
=
TO
14
200
P.
ATN*64
,
14-N
J
250 N.N
300 F ,X =
TO
5
310
P. AT
K+10*X,X;
320 N.X
400
F.X=6T056 STEP10
410
P
.AT K + X
,
"
s
"
;
420 N.X
999 G.999
What
is
the
POINT
of
all this?
The POINT(X,Y)
statement stands pretty
much
isolated
from
the other 3 graphics
state-
ments.
It
needs them, but they don't need
it
at
all.
POINT(X,Y)
interrogates (what
a
great technical
word) that graphics point on the screen
with the address of X,Y.
If
that point
is lit,
the
POINT
statement says
"1".
If
it is
dark, the
POINT
statement
says
"0". That's
really
all
there
is
to
it.
Of
such great simplicity great
power
is
derived.
Let's give
POINT
a little
exercise
before looking closer. Since
it
also
works
in
the calculator
mode, type
PRINT
POINTt
30 ,30)
Since
we had not
lit
30,30 the
answer came
back with
0.
It also
can be
abbreviated. Type:
P.P.
(
30,30)
Same
thing:
Interrogates
—
just asks a question;
but
it's
in logic
form
. . ..
true
or yes.™ 1 and
Mm
or rtogivesa fy
Tho
they can both be abbreviated
P.,
the paren-
thesis
following the second
P. tells
the
Computer
that
it is
POINT
and not
PRINT.
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137