In
computer programming
Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programming involves tasks such as anal ...
, operators are constructs defined within
programming languages
A programming language is a system of notation for writing computer program, computer programs. Most programming languages are text-based formal languages, but they may also be visual programming language, graphical. They are a kind of computer ...
which behave generally like
functions, but which differ
syntactically
In linguistics, syntax () is the study of how words and morphemes combine to form larger units such as phrases and sentences. Central concerns of syntax include word order, grammatical relations, hierarchical sentence structure ( constituency) ...
or
semantically
Semantics (from grc, σημαντικός ''sēmantikós'', "significant") is the study of reference, meaning, or truth. The term can be used to refer to subfields of several distinct disciplines, including philosophy, linguistics and compu ...
.
Common simple examples include arithmetic (e.g. addition with ), comparison (e.g. "
greater than" with
>
), and
logical operations (e.g.
AND
, also written
&&
in some languages). More involved examples include
assignment (usually
=
or
:=
),
field access in a record or
object (usually
.
), and the
scope resolution operator (often
::
or
.
). Languages usually define a set of built-in operators, and in some cases allow users to add new meanings to existing operators or even define completely new operators.
Syntax
Syntactically
In linguistics, syntax () is the study of how words and morphemes combine to form larger units such as phrases and sentences. Central concerns of syntax include word order, grammatical relations, hierarchical sentence structure ( constituency) ...
operators usually contrast to
functions. In most languages, functions may be seen as a special form of prefix operator with fixed
precedence
Precedence may refer to:
* Message precedence of military communications traffic
* Order of precedence, the ceremonial hierarchy within a nation or state
* Order of operations, in mathematics and computer programming
* Precedence Entertainment, a ...
level and associativity, often with compulsory
parentheses e.g.
Func(a)
(or
(Func a)
in
Lisp
A lisp is a speech impairment in which a person misarticulates sibilants (, , , , , , , ). These misarticulations often result in unclear speech.
Types
* A frontal lisp occurs when the tongue is placed anterior to the target. Interdental lispi ...
). Most languages support programmer-defined functions, but cannot really claim to support programmer-defined operators, unless they have more than prefix notation and more than a single precedence level. Semantically operators can be seen as special form of function with different calling notation and a limited number of parameters (usually 1 or 2).
The position of the operator with respect to its operands may be
prefix
A prefix is an affix which is placed before the stem of a word. Adding it to the beginning of one word changes it into another word. For example, when the prefix ''un-'' is added to the word ''happy'', it creates the word ''unhappy''. Particu ...
,
infix or
postfix, and the syntax of an
expression involving an operator depends on its
arity
Arity () is the number of arguments or operands taken by a function, operation or relation in logic, mathematics, and computer science. In mathematics, arity may also be named ''rank'', but this word can have many other meanings in mathematics. In ...
(number of
operand
In mathematics, an operand is the object of a mathematical operation, i.e., it is the object or quantity that is operated on.
Example
The following arithmetic expression shows an example of operators and operands:
:3 + 6 = 9
In the above exa ...
s), precedence, and (if applicable),
associativity. Most programming languages support
binary operators and a few
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
-x
, and postfix unary operators, such as
post-increment x++
; and binary operations are infix, such as
x + y
or
x = y
. Infix operations of higher arity require additional symbols, such as the
ternary operator ?: in C, written as
a ? b : c
– 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
1 2 3 4 +
.
Occasionally parts of a language may be described as "matchfix" or "circumfix" operators, either to simplify the language's description or implementation. A circumfix operator consists of two or more parts which enclose its operands. Circumfix operators have the highest precedence, with their contents being evaluated and the resulting value used in the surrounding expression. The most familiar circumfix operator are the parentheses mentioned above, used to indicate which parts of an expression are to be evaluated before others. Another example from physics is the
inner product notation of Dirac's
bra–ket notation. Circumfix operators are especially useful to denote operations that involve many or varying numbers of operands.
The specification of a language will specify the syntax the operators it supports, while languages such as
Prolog
Prolog is a logic programming language associated with artificial intelligence and computational linguistics.
Prolog has its roots in first-order logic, a formal logic, and unlike many other programming languages, Prolog is intended primarily a ...
that support programmer-defined operators require that the syntax be defined by the programmer.
Semantics
The semantics of operators particularly depends on value, evaluation strategy, and argument passing mode (such as boolean short-circuiting). Simply, an
expression involving an operator is evaluated in some way, and the resulting
value may be just a value (an r-value), or may be an object allowing assignment (an l-value).
In simple cases this is identical to usual function calls; for example, addition
x + y
is generally equivalent to a function call
add(x, y)
and less-than comparison
x < y
to
lt(x, y)
, meaning that the arguments are evaluated in their usual way, then some function is evaluated and the result is returned as a value. However, the semantics can be significantly different. For example, in assignment
a = b
the target
a
is not evaluated, but instead its ''location'' (address) is used to store the value of
b
– corresponding to
call-by-reference semantics. Further, an assignment may be a statement (no value), or may be an expression (value), with the value itself either an r-value (just a value) or an l-value (able to be assigned to). As another example, the
scope resolution operator :: and the element access operator . (as in
Foo::Bar
or
a.b
) operate not on values, but on ''names'', essentially
call-by-name semantics, and their value is a name.
Use of l-values as operator operands is particularly notable in unary
increment and decrement operators
Increment and decrement operators are unary operators that ''add'' or ''subtract'' one, to or from their operand, respectively.
They are commonly implemented in imperative programming languages. C-like languages feature two versions (pre- and ...
. In C, for instance, the following statement is legal and well-defined, and depends on the fact that array indexing returns an l-value:
x = ++a
An important use is when a left-associative binary operator modifies its left argument (or produces a side effect) and then evaluates to that argument as an l-value. This allows a sequence of operators all affecting the original argument, allowing a
fluent interface, similar to
method cascading. A common example is the
<<
operator in the C++
iostream
library, which allows fluent output, as follows:
cout << "Hello" << " " << "world!" << endl;
User-defined operators
A language may contain a fixed number of built-in operators (e.g. , etc. in
C and C++,
PHP
PHP is a General-purpose programming language, general-purpose scripting language geared toward web development. It was originally created by Danish-Canadian programmer Rasmus Lerdorf in 1993 and released in 1995. The PHP reference implementati ...
), or it may allow the creation of programmer-defined operators (e.g.
Prolog
Prolog is a logic programming language associated with artificial intelligence and computational linguistics.
Prolog has its roots in first-order logic, a formal logic, and unlike many other programming languages, Prolog is intended primarily a ...
,
Seed7,
F#,
OCaml,
Haskell). Some programming languages restrict operator symbols to special characters like or while others allow also names like
div
(e.g.
Pascal).
Most languages have a built-in set of operators, but do not allow user-defined operators, as this significantly complicates parsing. Many languages only allow operators to be used for built-in types, but others allow existing operators to be used for user-defined types; this is known as
operator overloading. Some languages allow new operators to be defined, however, either at compile time or at run time. This may involve meta-programming (specifying the operators in a separate language), or within the language itself. Definition of new operators, particularly runtime definition, often makes correct
static analysis of programs impossible, since the syntax of the language may be Turing-complete, so even constructing the syntax tree may require solving the halting problem, which is impossible. This occurs for
Perl
Perl is a family of two High-level programming language, high-level, General-purpose programming language, general-purpose, Interpreter (computing), interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it ...
, for example, and some dialects of
Lisp
A lisp is a speech impairment in which a person misarticulates sibilants (, , , , , , , ). These misarticulations often result in unclear speech.
Types
* A frontal lisp occurs when the tongue is placed anterior to the target. Interdental lispi ...
.
Examples
Common examples that differ syntactically are mathematical
arithmetic operations, e.g. ">" for "
greater than", with names often outside the language's set of
identifiers
An identifier is a name that identifies (that is, labels the identity of) either a unique object or a unique ''class'' of objects, where the "object" or class may be an idea, physical countable object (or class thereof), or physical noncountable ...
for functions, and called with a syntax different from the language's syntax for calling functions. As a function, "greater than" would generally be named by an identifier, such as
gt
or
greater_than
and called as a function, as
gt(x, y)
. Instead, the operation uses the special character
>
(which is tokenized separately during
lexical analysis), and infix notation, as
x > y
.
Common examples that differ semantically (by argument passing mode) are boolean operations, which frequently feature
short-circuit evaluation: e.g. a short-circuiting conjunction (X AND Y) that only evaluates later arguments if earlier ones are not false, in a language with strict call-by-value functions. This behaves instead similarly to if/then/else.
Less common operators include:
*
Comma operator:
e, f
*
Dereference operator:
*p
and address-of operator:
&x
*
?: or ternary operator:
number = spell_out_numbers ? "forty-two" : 42
**
Elvis operator
In certain computer programming languages, the Elvis operator, often written ?:, is a binary operator that returns its first operand if that operand evaluates to a true value, and otherwise evaluates and returns its second operand. This is ident ...
:
x ?: y
*
Null coalescing operator
The null coalescing operator (called the Logical Defined-Or operator in Perl) is a binary operator that is part of the syntax for a basic conditional expression in several programming languages, including C#, PowerShell as of version 7.0.0, Perl ...
:
x ?? y
*
Spaceship operator (for
three-way comparison):
x <=> y
Compilation
A compiler can implement operators and functions with
subroutine calls or with
inline code. Some built-in operators supported by a language have a direct mapping to a small number of
instructions commonly found on
central processing units
A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, an ...
, though others (''e.g.'' '+' used to express
string concatenation
In formal language theory and computer programming, string concatenation is the operation of joining character strings end-to-end. For example, the concatenation of "snow" and "ball" is "snowball". In certain formalisations of concatenatio ...
) may have complicated implementations.
Operator overloading
In some programming languages an operator may be ''ad hoc polymorphic'', that is, have definitions for more than one kind of data, (such as in
Java
Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...
where the operator is used both for the addition of numbers and for the concatenation of strings). Such an operator is said to be ''overloaded''. In languages that support operator overloading by the programmer (such as
C++) but have a limited set of operators, operator overloading is often used to define customized uses for operators.
In the example
IF ORDER_DATE > "12/31/2011" AND ORDER_DATE < "01/01/2013" THEN CONTINUE ELSE STOP
, the operators are: ">" (greater than), "AND" and "<" (less than).
Operand coercion
Some languages also allow for the operands of an operator to be implicitly converted, or ''
coerced
Coercion () is compelling a party to act in an involuntary manner by the use of threats, including threats to use force against a party. It involves a set of forceful actions which violate the free will of an individual in order to induce a de ...
'', to suitable data types for the operation to occur. For example, in
Perl
Perl is a family of two High-level programming language, high-level, General-purpose programming language, general-purpose, Interpreter (computing), interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it ...
coercion rules lead into
12 + "3.14"
producing the result of
15.14
. The text
"3.14"
is converted to the number 3.14 before addition can take place. Further,
12
is an integer and
3.14
is either a floating or fixed-point number (a number that has a decimal place in it) so the integer is then converted to a floating point or fixed-point number respectively.
JavaScript
JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of Website, websites use JavaScript on the Client (computing), client side ...
follows opposite rules—finding the same expression above, it will convert the integer
12
into a string
"12"
, then concatenate the two operands to form
"123.14"
.
In the presence of coercions in a language, the programmer must be aware of the specific rules regarding operand types and the operation result type to avoid subtle programming mistakes.
Operator features in programming languages
The following table shows the operator features in several programming languages:
See also
*
Relational operator
Notes
References
{{reflist
Programming constructs