Editing Operator (computer programming) (section)

== Differences from functions ==

=== Syntax ===
Many operators differ syntactically from user-defined functions. In most languages, a function is [[prefix notation]] with fixed [[Order of operations|precedence]] level and associativity and often with compulsory [[parentheses]] (e.g. <code>Func(a)</code> or <code>(Func a)</code> in [[Lisp (programming language)|Lisp]]). In contrast, many operators are infix notation and involve different use of delimiters such as parentheses. 

In general, an operator may be prefix, infix, postfix, [[matchfix]], [[circumfix]] or bifix,<ref>{{Cite web|url=https://reference.wolfram.com/language/tutorial/OperatorInputForms.html.en|title=Operator Input Forms—Wolfram Language Documentation|website=reference.wolfram.com}}</ref><ref>{{Cite web|url=http://maxima.sourceforge.net/docs/manual/maxima_7.html|title=Maxima 5.42.0 Manual: 7. Operators|website=maxima.sourceforge.net}}</ref><ref>{{Cite web|url=https://mythryl.org/my-Prefix__Postfix_and_Circumfix_Operators.html|title=Prefix, Postfix and Circumfix Operators|website=mythryl.org}}</ref><ref>{{Cite web|url=http://doc.perl6.org/language/operators#___top|title=Operators|website=doc.perl6.org}}</ref><ref name=Pribavkina>{{cite conference|ref= Pribavkina| last1 = Pribavkina| last2= Rodaro| date= August 2010| title= State Complexity of Prefix, Suffix, Bifix and Infix Operators on Regular Languages |journal= Lecture Notes in Computer Science| type= Conference Article| series= Developments in Language Theory| language= English| conference= 14th International Conference on Developments in Language Theory| location= London Ontario| publisher= Springer| publication-date= 2010| issue= 6224| pages= 376–377 | doi=10.1007/978-3-642-14455-4_34| isbn= 978-3-642-14454-7| issn= 0302-9743}}</ref> and the syntax of an [[expression (computer science)|expression]] involving an operator depends on its [[arity]] (number of [[operand]]s), precedence, and (if applicable), [[Operator associativity|associativity]]. Most programming languages support [[binary operator]]s and a few [[unary operation|unary operators]], with a few supporting more operands, such as the [[?:]] operator in C, which is ternary. There are prefix unary operators, such as unary minus <code>-x</code>, and postfix unary operators, such as [[post-increment]] <code>x++</code>; and binary operations are infix, such as <code>x + y</code> or <code>x = y</code>. Infix operations of higher arity require additional symbols, such as the [[ternary operator]] ?: in C, written as <code>a ? b : c</code> – indeed, since this is the only common example, it is often referred to as ''the'' ternary operator. Prefix and postfix operations can support any desired arity, however, such as <code>1 2 3 4 +</code>.

=== Semantics ===
The semantics of an operator may significantly differ from that of a normal function. For reference, addition is evaluated like a normal function. For example, <code>x + y</code> can be equivalent to a function <code>add(x, y)</code> in that the arguments are evaluated and then the functional behavior is applied. However, [[Assignment_(computer_science)|assignment]] is different. For example, given <code>a = b</code> the target <code>a</code> is ''not'' evaluated. Instead its value is replaced with the value of <code>b</code>. The [[scope resolution operator|scope resolution]] and element access operators (as in <code>Foo::Bar</code> and <code>a.b</code>, respectively, in the case of e.g. [[C++]]) operate on identifier names; not values.

In C, for instance, the array indexing operator can be used for both read access as well as assignment. In the following example, the  [[increment and decrement operators|increment operator]] reads the element value of an array and then assigns the element value.
<syntaxhighlight lang=c>
++a[i];
</syntaxhighlight>

The C++ <code>&lt;&lt;</code> operator allows for [[fluent interface|fluent]] syntax by supporting a sequence of operators that affect a single argument. For example:
<syntaxhighlight lang=cpp>
cout << "Hello" << " " << "world!" << endl;
</syntaxhighlight>