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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 (e.g. "x+1;") unless it is a part of an expression statement that induces side-effects (e.g. "y=x+1;" or "func1(func2());").
Note that the formal notion of a side effect is a change to the abstract state of the running program. Another class of side effects are changes to the concrete state of the computational system, such as loading data into cache memories. Languages which are often described as "side effect–free" will generally still have concrete side effects which can be exploited, for example, in [[side-channel attack]]s.
==See also==
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