Commodore Plus 4 - Page 20

8 The BASIC Language
Logical OR
OR requires only one of the two conditions to be met for the compound expres
sion to be true. An ORed comparison is false only when both values are false. For
example
10 INPUT "AGE, ANNUAL INC0ME";X, Y
20 IF X=>60 OR Y<=10000 THEN PRINT "ELIGIBLE": ELSE PRINT
"INELIGIBLE"
RUN
AGE, ANNUAL INCOME ? 60, 15000
ELIGIBLE
RUN
AGE, ANNUAL INCOME ? 65, 9900
ELIGIBLE
RUN
AGE, ANNUAL INCOME ? 55, 12000
INELIGIBLE
This modification of the previous program shows the difference between AND
and OR. In the first program, the input 60 and 15000 makes the IF command false
because both conditions must be met before the IF command is true. In the
second program with OR in the IF command, the same input makes the IF
command true because only one of the two conditions has to be met for the whole
IF command to be true, the third execution shows that the only time ORed IF
commands are false is when NEITHER condition is met.
Logical NOT
NOT is somewhat different from AND and OR. NOT does not compare two
values. Instead, NOT lets you negate any value or comparison operator. For
example, we will add NOT to an IF command that compares a value to see if it is
greater than another value: IF NOT X > Y. Without the NOT, this command
checks to see if X is greater than Y. When NOT is added, this command checks to
see if X is NOT greater than Y; in other words, if X is less than or equal to Y.
When you use NOT, you must type NOT before the values you are comparing.
This may seem awkward because we would say "if X is NOT greater than Y," but