Expression (computer science)

From Wikipedia, the free encyclopedia
Jump to: navigation, search

An expression in a programming language is a combination of explicit values, constants, variables, operators, and functions that are interpreted according to the particular rules of precedence and of association for a particular programming language, which computes and then produces (returns, in a stateful environment) another value. This process, like for mathematical expressions, is called evaluation. The value can be of various types, such as numerical, string, and logical.

For example, 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.[1][2]

In C and most C-derived languages, a call to a function with a void return type is a valid expression, of type void.[3] 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 disregard the result of the expression.

See also[edit]

References[edit]

  1. ^ Javascript expressions, Mozilla Accessed July 6, 2009
  2. ^ Programming in C Accessed July 6, 2009
  3. ^ ISO/IEC 9899:1999 section 6.3.2.2, accessed August 31, 2009

External links[edit]