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| Keyword | Abbreviation | Token (hex) | Version(s) | Classification | | NOT | N{Shift+O} | A8 | 1.0 to 7.0 | Operator (5) |
NOT expression | Parameters | Type | Legal Value(s) | Default Value | Note(s) | | expression | Float or Integer | -32768 to +32767 | | |
| Returns | Type | Value(s) | Note(s) | | result | Integer | -32768 to +32767 | Will be -1 or 0 if expression is 0 or -1 |
Evaluate a bit-wise boolean operation.
The NOT operator is often used in logical expressions, and may be considered a logical operator. However, this is not really the case and can have nasty consequences if you're not aware of how it actually functions. First, if the expression is a string, a TYPE MISMATCH ERROR is generated. Next, if the expression is floating-point then it is converted to an integer; if the result is not a legal value (see above) then ILLEGAL QUANTITY ERROR is generated. Finally, each of the 16 bits in the integer is complemented to produce the result. If the expression is 0 or -1 then the result will be -1 or 0, which is completely logical. BASIC operators which return a boolean result always return -1 for true or 0 for false so this works well most of the time. However, using NOT with other non-zero values (besides -1) will produce another non-zero value. This is not logical, which is why this is more properly called a bit-wise boolean operation. Examples are provided below, but to really understand them, you need to know how to convert a decimal number into binary (and back again). I won't try to explain that here; you may find this web page helpful for experimenting, or use a calculator. Also important to note is that logical and bit-wise negation (discussed on this page) are different (though similar) to comparison for inequality; see the less and more operators (< and >). The NOT operator has a very low operator priority (5), which is less than all arithmetic and relational operators. Its priority, however, is greater than the AND and OR bit-wise operators. Of course the user may invoke parentheses to change the order of evaluation. Boolean/Logical operators (like NOTl) are often used with IF, DO, and LOOP. Some "logical" examples:
PRINT NOT "A"
?TYPE MISMATCH ERROR
READY.
A=1 : B=2
READY.
PRINT NOT A>B
-1
READY.
PRINT NOT A<B
0
READY.
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Some examples about operator priority:
A=1 : B=2 : PRINT NOT A<B AND A>B
0
READY.
PRINT NOT (A<B AND A>B)
-1
READY.
|
Some examples demonstrating bit-wise complement:
A=1 : REM binary 0000 0000 0000 0001
READY.
PRINT NOT A
-2 : REM binary 1111 1111 1111 1110 -- not logical!
READY.
PRINT (NOT A) AND A <>0 : REM the () are unneccessary
-2 : REM also not logical, because of NOT A
READY.
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