Commodore Plus 4 - Page 21

The Elements of BASIC 9
you must put the NOT just before the value or comparison to negate or the
command will cause a syntax error, which always stops a program. You might
think of NOT as changing the meaning of X > Y to "unless X is greater than Y."
The following comparisons show how NOT affects comparison operators. The
comparisons on the right are the same as those on the left:
X>Y same as NOTXOY
X<=Y same as NOTX>Y
X O Y same as NOT X = Y
X = Y same as NOTXOY
The last NOT clause contains a double negative: NOT and <> (not equal).
Double negatives, though discouraged in most English applications, are accept
able in BASIC. But like double negatives in English, double negatives in BASIC
cancel each other, so NOT X O Y is the same as X = Y.
This short program uses NOT to make the opposite of the comparison opera
tor typed in the IF command:
10 INPUT "WHAT'S YOUR AGE"; A
20 IF NOT A => 21 THEN PRINT "USER IS A MINOR": ELSE PRINT
"OK"
RUN
WHAT'S YOUR AGE ? 20
USER IS A MINOR
RUN
WHAT'S YOUR AGE ? 21
OK
The NOT makes the greater-than-or-equal-to symbol mean this: unless A is
greater-than-or-equal-to 21, THEN print USER IS A MINOR. The comparison
is the same as IF A < 21.
Exclusive OR (XOR)
The exclusive OR, which is called XOR, is not a standard logical operator. XOR
is used in machine language (EOR), and it is used in the WAIT command to
invert the comparison of two bits. When both XORed bits have the same value,