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In a [[programming language]], an '''expression''' is a combination of one or more explicit [[value (computer science)|value]]s, [[Constant (programming)|constants]], [[variable (programming)|variable]]s, [[operator (programming)|operator]]s, and [[function (programming)|function]]s that the programming language interprets (according to its particular [[Order of operations|rules of precedence]] and of association) and computes to produce ("to return", in a [[state (computer science)|stateful]] environment) another value.

== Description ==

This process, as for [[mathematical expression]]s, is called evaluation.

The returned value can be of various [[Data type|type]]s, such as numerical, string, and logical.

== Example ==

For example, <code>2+3</code> is an arithmetic and programming expression which evaluates to 5. A variable is an expression because it denotes a value in memory, so <code>y+6</code> is an expression. An example of a relational expression is <code>4≠4</code>, which evaluates to false.<ref>[https://developer.mozilla.org/en/Core_JavaScript_1.5_Guide/Expressions Javascript expressions, Mozilla] Accessed July 6, 2009</ref><ref>[https://www.cs.drexel.edu/~rweaver/COURSES/ISTC-2/TOPICS/expr.html Programming in C] Accessed July 6, 2009</ref>

In [[C (programming language)|C]] and most C-derived languages, a call to a function with a [[Void type|void]] return type is a valid expression, of type void.<ref>
[http://www.open-std.org/JTC1/SC22/WG14/www/docs/n1256.pdf ISO/IEC 9899:1999] section 6.3.2.2, accessed August 31, 2009
</ref>
Values of type void cannot be used, so the value of such an expression is always thrown away.

== Side effects ==

In many programming languages a function, and hence an expression containing a function, may have [[Side effect (computer science)|side effects]]. 

An expression with side effects does not normally have the property of [[referential transparency (computer science)|referential transparency]].

In many languages (e.g. C++), expressions may be ended with a semicolon (<code>;</code>) to turn the expression into an expression [[Statement (programming)|statement]].

This asks the implementation to evaluate the expression for its side-effects only, and to disregard the result of the expression.

== See also ==

* [[Boolean expression]]
* [[Computer program]]
* [[Computer science]]
* [[Data type]]
* [[Evaluation strategy]]
* [[Expression (mathematics)]]
* [[Mathematical expression]]
* [[Programming language]]
* [[Statement (programming)]] (contrast)

== External links ==

* [https://en.wikipedia.org/wiki/Expression_(computer_science) Expression (computer science)] @ Wikipedia

[[Category:Computer science]]
[[Category:Computer programming]]