Editing Assignment (computer science) (section)

==Value of an assignment==
In some programming languages, an assignment statement returns a value, while in others it does not.

In most [[expression-oriented programming languages]] (for example, [[C (programming language)|C]]), the assignment statement returns the assigned value, allowing such idioms as <code>x = y = a</code>, in which the assignment statement <code>y = a</code> returns the value of <code>a</code>, which is then assigned to <code>x</code>. In a statement such as {{code|2=c|1=while ((ch = getchar()) != EOF) {…} }}, the return value of a function is used to control a loop while assigning that same value to a variable.

In other programming languages, [[Scheme (programming language)|Scheme]] for example, the return value of an assignment is undefined and such idioms are invalid.

In [[Haskell (programming language)|Haskell]],<ref name="haskell">{{cite book |last=Hudak |first=Paul |year=2000 |title=The Haskell School of Expression: Learning Functional Programming Through Multimedia |location=Cambridge |publisher=Cambridge University Press |isbn=0-521-64408-9}}</ref> there is no variable assignment; but operations similar to assignment (like assigning to a field of an array or a field of a mutable data structure) usually evaluate to the [[unit type]], which is represented as <code>()</code>. This type has only one possible value, therefore containing no information. It is typically the type of an expression that is evaluated purely for its side effects.