Boolean expression: Difference between revisions

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{{Short description|Expression in a computer program}}

I said boolean search not boolean expression you moron.

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 '''True/False''' or '''Yes/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

| contribution = Chapter 2. Boolean Expressions

| isbn = 9780387941158

| page = 25ff

| publisher = Springer

| series = Monographs in Computer Science

| title = A Logical Approach to Discrete Math

| url = https://books.google.com/books?id=ZWTDQ6H6gsUC&pg=PA25

| year = 1993}}.</ref>

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

| last = van Melkebeek | first = Dieter

| isbn = 9783540414926

| page = 22

| publisher = Springer

| series = [[Lecture Notes in Computer Science]]

| title = Randomness and Completeness in Computational Complexity

| url = https://books.google.com/books?id=-S0zCjOAIVwC&pg=PA22

| volume = 1950

| year = 2000}}.</ref>

==Boolean operators==

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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}}).