Radio Shack TRS-80 User Manual page 152

Logical Variations
This
next
program example mixes equals
signs,
greater -than
and
less-than
in
the
same
pro-
gram.
It
determines and reports
whether the
two numbers you input
are
both
positive,
both
negative, or
have different signs.
Analyze
the
program.
Note
the parentheses.
They
tell
you
to shift
your
thinking to "logi-
cal".
Type
it
in
and
RUN.
10
INPUT
"FIRST NUMBER IS"
;X
20
INPUT "SECOND NUMBER IS"
;Y
30 IF (X>=0)
*
(
Y>=0) THEN
70
40 IF
(X<0)
*
(Y<0)
THEN 90
50
PRINT "OPPOSITE SIGNS"
60
END
70
PRINT "BOTH POSITIVE
"
80 END
90
PRINT "BOTH NEGATIVE"
With Graphics Too, Yet
Yes, the
logical
symbols
also
work along with the graphics statements. See
if
you
can figure
out the
surprise
caused
by
the
logical
OR
in line 40.
Type
this
program
in,
and
RUN.
10
CLS
20 FOR X=0 TD 127
30
FOR Y=0 TO 47
40 IF
CX>=64) *
(Y>=24) THEN
60
50 SET
(X
t
Y)
60
NEXT
Y
70
NEXT
X
150