Logical Operators:

OR, AND, and NOT are used as logical operators in IF statements.
OR and AND operate on the logical expressions between which
they are placed, while NOT operates on the logical expression
following it.  Remember that the value of a logical expression
must be either -1 (true) or 0 (false).

OR
When OR is placed between two logical expressions, the total
expression is true if either or both of the two logical expressions
are true.

AND
When AND is placed between two logical expressions, the total
expression is true if and only if both of the two logical
expressions are true.

NOT
When NOT is placed before a logical expression, the total
expression is true if the logical expression is false,
and the total expression is false if the logical expression
is true.

Below are truth tables for the three logical operators, where
T stands for TRUE (-1), F stands for FALSE (0),
and A and B are logical expressions:

    A    B    A OR B    A AND B    NOT A

    F    F      F          F         T
    F    T      T          F         T
    T    F      T          F         F
    T    T      T          T         F

Examples:

0 AND 1 equals 0
1 AND 1 equals 1
2 AND 1 equals 0
2 AND 3 equals 2

0 OR 1 equals 1
1 OR 1 equals 1
2 OR 1 equals 3
2 OR 3 equals 3

NOT 0 equals -1
NOT -1 equals 0
NOT 1 equals -2









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