Logical And

Logical AND is a logical operation which has the following truth table:

• False AND False = False
• False AND True = False
• True AND False = False
• True AND True = True

More generally:

• AND is true only when all of its arguments are true
• AND is false if any of its arguments are false.

This applies for any number of arguments to AND.

Stated another way (for C and C++ programmers, AND = &&)

• non-zero && non-zero = true
• zero && anything = false

Of course, in C, && is not LogicalAnd but rather ShortCircuitAnd? (the second argument is not evaluated unless the first argument is True).

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Logical AND is not to be confused with the BitwiseAnd? operator. BitwiseAnd? operations are often used as a bit mask to clear certain bits without affecting others. For example, 00001111 AND 10101010 results in 00001010. (This was confusing when used in Commodore BASIC, because non-programmers think "and" means "plus": POKE 1,PEEK(1) AND 251 would clear bit 2, not add four.)

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For those of us who need to use ThreeValuedLogic, Logical and has the following additional truth values:

• False and Unknown = False
• True and Unknown = Unknown
• Unknown and Unknown = Unknown

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CategoryLogic