Apple IIe - Page 60

60 Apple lie Users Handbook
of +1 for a true value.). An operand of a logical operator is
evaluated as false if it is equal to zero.
The result
of a logical operation is also a number, which if
non-zero is considered true, and false if it is zero.
The
following are examples of the use of logical operators in
combination with relational operators in decision making.
IF X >10 OR Y<O THEN 900
IF A>O AND B>O THEN 200
B=-1 :PRINT NOT B
In
the first example , the result of the logical operation will be
true if variable X has a value greater than 10 or if variable Y has a
value
less than 0. Otherwise, it will be false. If the result of the
logical operation is true , the program will branch to line 900.
Otherwise , it will continue to the next statement.
In the second
example , the result of the logical operation will be
true only if the value of both variables A and Bare greater than
zero.
If the result of the logical operation is true , program
control will branch to line 200 . Otherwise , program control will
branch to the next line .
In
the third example , Bis set to a value of-1 (true). The value of
NOT B is then printed . This will be 0 or false.
Illustration 3-3 contains tables that may prove of help when
evaluating program statements using logical operators in
combination with relational operators.