An expression in a programming language

Programming language

A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....

 is a combination of explicit value

Value (computer science)

In computer science, a value is an expression which cannot be evaluated any further . The members of a type are the values of that type. For example, the expression "1 + 2" is not a value as it can be reduced to the expression "3"...

s, constants

Constant (programming)

In computer programming, a constant is an identifier whose associated value cannot typically be altered by the program during its execution...

, variable

Variable (programming)

In computer programming, a variable is a symbolic name given to some known or unknown quantity or information, for the purpose of allowing the name to be used independently of the information it represents...

s, operator

Operator (programming)

Programming languages typically support a set of operators: operations which differ from the language's functions in calling syntax and/or argument passing mode. Common examples that differ by syntax are mathematical arithmetic operations, e.g...

s, and functions that are interpreted according to the particular rules of precedence

Order of operations

In mathematics and computer programming, the order of operations is a rule used to clarify unambiguously which procedures should be performed first in a given mathematical expression....

 and of association for a particular programming language, which computes and then produces (returns, in a stateful

State (computer science)

In computer science and automata theory, a state is a unique configuration of information in a program or machine. It is a concept that occasionally extends into some forms of systems programming such as lexers and parsers....

 environment) another value. This process, like for mathematical expressions, is called evaluation. The value can be of various type

Data type

In computer programming, a data type is a classification identifying one of various types of data, such as floating-point, integer, or Boolean, that determines the possible values for that type; the operations that can be done on values of that type; the meaning of the data; and the way values of...

s, 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 is a pointer to a value in memory, so y+6 is an expression. An example of a relational expression is 44 which evaluates to true.

In C

C (programming language)

C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....

 and most C-derived languages, a call to a function with a void

Void type

The void type, in several programming languages derived from C and Algol68, is the type for the result of a function that returns normally, but does not provide a result value to its caller. Usually such functions are called for their side effects, such as performing some task or writing to their...

 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.

A function, and hence an expression containing a function, may have side effect

Side effect (computer science)

In computer science, a function or expression is said to have a side effect if, in addition to returning a value, it also modifies some state or has an observable interaction with calling functions or the outside world...

s. An expression with side effects does not normally have the property of referential transparency. In many languages (e.g. C++) statements may be ended with a semicolon ';' to turn the expression into an expression statement

Statement (programming)

In computer programming a statement can be thought of as the smallest standalone element of an imperative programming language. A program written in such a language is formed by a sequence of one or more statements. A statement will have internal components .Many languages In computer programming...

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

• Statement (programming)
  Statement (programming)
  In computer programming a statement can be thought of as the smallest standalone element of an imperative programming language. A program written in such a language is formed by a sequence of one or more statements. A statement will have internal components .Many languages In computer programming...
  
   (contrast)
• Boolean expression
  Boolean expression
  In computer science, a Boolean expression is an expression in a programming language that produces a Boolean value when evaluated, i.e. one of true or false...
  
  
• Expression (mathematics)
  Expression (mathematics)
  In mathematics, an expression is a finite combination of symbols that is well-formed according to rules that depend on the context. Symbols can designate numbers , variables, operations, functions, and other mathematical symbols, as well as punctuation, symbols of grouping, and other syntactic...
  
  
• evaluation strategy
  Evaluation strategy
  In computer science, an evaluation strategy is a set of rules for evaluating expressions in a programming language. Emphasis is typically placed on functions or operators: an evaluation strategy defines when and in what order the arguments to a function are evaluated, when they are substituted...