QBasic 1.1: Boolean Operators
Explanation
Boolean Operators
Boolean operators perform bit manipulations, Boolean operations, or tests on multiple relations. They return a true (nonzero) or false (zero) value to be used in making a decision.
Worth knowing
Useful and cross-version information about the programming environments of QBasic, QuickBasic and Visual Basic for DOS.
Syntax
| result = expression1 boolean-operator expression2 |
Description / Parameter(s)
| boolean-operator |
Any of the following Boolean operators: |
| |
| NOT | Bit-wise complement |
| AND | Conjunction |
| OR | Disjunction (inclusive "or") |
| XOR | Exclusive "or" |
| EQV | Equivalence |
| IMP | Implication |
|
| Each operator returns results as indicated in the following truth table. T is true (nonzero); F is false (zero): |
| |
| Expression1 |
Expression2 |
NOT |
AND |
OR |
XOR |
EQV |
IMP |
| T | T | F | T | T | F | T | T |
| T | F | F | F | T | T | F | F |
| F | T | T | F | T | T | F | T |
| F | F | T | F | F | F | T | T |
|
| Boolean operations are performed after arithmetic and relational operations in order of precedence. |
| Expressions are converted to integers or long integers before a Boolean operation is performed. |
| If the expressions evaluate to 0 or -1, a Boolean operation returns 0 or -1 as the result. Because Boolean operators do bit-wise calculations, using values other than 0 for false and -1 for true may produce unexpected results. |