Boolean expression: Difference between revisions

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{{Short description|Expression in a computer program that produces either "true" or "false" when evaluated}}

In [[computer science]], a '''Boolean expression''' (also known as '''logical expression''') is an [[Expression (programming)|expression]] used in [[programming language]]s that produces a [[Boolean value]] when evaluated. A Boolean value is either '''true''' or '''false'''. A Boolean expression may be composed of a combination of the Boolean constants '''trueTrue/False''' or '''falseYes/No''', [[Boolean data type|Boolean-typed]] variables, Boolean-valued operators, and [[Boolean-valued function]]s.<ref>{{citation

| last1 = Gries | first1 = David | author1-link = David Gries

| last2 = Schneider | first2 = Fred B. | author2-link = Fred B. Schneider

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| year = 1993}}.</ref>

Boolean expressions correspond to [[propositional formula]]s in logic and are aassociated [[special case]] ofto [[Boolean circuit]]s.<ref>{{citation

| last = van Melkebeek | first = Dieter

| isbn = 9783540414926

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Some languages, e.g., [[Perl]] and [[Ruby (programming language)|Ruby]], have two sets of Boolean operators, with identical functions but different precedence. Typically these languages use '''and''', '''or''' and '''not''' for the lower precedence operators.

Some programming languages derived from [[PL/I]] have a bit string type and use BIT(1) rather than a separate Boolean type. In those languages the same operators serve for booleanBoolean operations and bitwise operations. The languages represent OR, AND, NOT and EXCLUSIVE OR by "|", "&", "¬" (infix) and "¬" (prefix).

===Short-circuit operators===

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*The expression {{code|3 > 5}} is evaluated as {{samp|false}}.

*{{code|1=5>=3}} and {{code|1=3<=5}} are equivalent Boolean expressions, both of which are evaluated as {{samp|true}}.

*<code>[[typeof]] true</code> and <code>typeof false</code> return {{samp|boolean}}

*Of course, most Boolean expressions will contain at least one variable ({{code|X > 3}}), and often more ({{code|X > Y}}).