Expression (computer science)
An expression in a programming language is a combination of one or more explicit values, constants, variables, operators, and functions that the programming language interprets (according to its particular rules of precedence and of association) and computes to produce ("to return", in a stateful environment) another value. This process, as for mathematical expressions, is called evaluation. The returned value can be of various types, such as numerical, string, and logical.
2+3 is an arithmetic and programming expression which evaluates to 5. A variable is an expression because it denotes a value in memory, so
y+6 is an expression. An example of a relational expression is
4≠4, which evaluates to false.
In C and most C-derived languages, a call to a function with a void return type is a valid expression, of type void. Values of type void cannot be used, so the value of such an expression is always thrown away.
In many programming languages a function, and hence an expression containing a function, may have side effects. An expression with side effects does not normally have the property of referential transparency. In many languages (e.g. C++), expressions may be ended with a semicolon (
;) to turn the expression into an expression statement. This asks the implementation to evaluate the expression for its side-effects only, and to disregard the result of the expression.