Conditional statement
Encyclopedia
In computer science
, conditional statements, conditional expressions and conditional constructs are features of a programming language
which perform different computations or actions depending on whether a programmer-specified boolean
condition evaluates to true or false. Apart from the case of branch predication
, this is always achieved by selectively altering the control flow
based on some condition.
In imperative programming
languages, the term "conditional statement
" is usually used, whereas in functional programming
, the terms "conditional expression
" or "conditional construct" are preferred, because these terms all have distinct meanings.
Although dynamic dispatch
is not usually classified as a conditional construct, it is another way to select between alternatives at runtime.
form) looks like this: (The example is actually perfectly valid Visual Basic or QuickBASIC syntax.)
If (predicate)
Then
(consequent)
Else
(alternative)
End If
When an interpreter
finds an
condition - for example,
After either branch has been executed, control
returns to the point after the
In early programming languages, especially some dialects of BASIC
in the 1980s home computer
s, an
which allows (virtually) arbitrary statements to be put in statement blocks inside an
family of languages, and ALGOL-like languages such as Pascal
and Modula-2
influenced modern BASIC variants for many years. While it is possible while using only
, its derivatives (including C++
and C#), Java
, JavaScript
and Visual Basic
(all versions including .NET).
language:
if condition then
-- statements;
elsif condition then
-- more statements
elsif condition then
-- more statements;
...
else
-- other statements;
end if;
for
In some other languages, such as C
and Java
,
, which provides the keyword
uses the special keyword
C and Java implementations, however, do have a disadvantage that each
and C-like languages conditional expressions take the form of a ternary operator called the conditional expression operator, ?:
, which follows this template:
(condition)?(evaluate if condition was true):(evaluate if condition was false)
This means that conditions can be inlined into expressions, unlike with if statements, as shown here using C syntax:
//Invalid in most programming languages. One of exceptions is Ruby
my_variable = if(x > 10) { "foo" } else { "bar" };
//Valid
my_variable = (x > 10)?"foo":"bar";
To accomplish the same as the second (correct) line above, using a standard if/else statement, this would take more than one line of code (under standard layout conventions):
if (x > 10)
my_variable = 'foo';
else
my_variable = 'bar';
ALGOL 60
and some other members of the ALGOL
family have the
In ALGOL:
myvariable := if x > 10 then 1 else 2
In the Lisp dialects Scheme and Common Lisp
, the former of which was inspired to a great extent by ALGOL:
;; Scheme
(define myvariable (if (> x 10) 1 2)) ; Assigns ‘myvariable’ to 1 or 2, depending on the value of ‘x’
;; Common Lisp
(let ((x 5))
(setq myvariable (if (> x 10) 1 2))) ; Assigns ‘myvariable’ to 2
and some other languages, a function called
98, there is only an if expression, no if statement, and the
in recursive functions.
Because Haskell is lazy
, it is possible to write control structures,. such as if, as ordinary expressions; the lazy evaluation means that an if function can evaluate only the condition and proper branch (where a strict language would evaluate all three). It can be written like this:
if' :: Bool -> a -> a -> a
if' True x _ = x
if' False _ y = y
, 
, 
. This was the earliest conditional statement in Fortran. :
IF (e) label1, label2, label3
Where e is any numeric expression (not necessarily an integer); this is equivalent to
IF (e .LT. 0) GOTO label1
IF (e .EQ. 0) GOTO label2
IF (e .GT. 0) GOTO label3
Because this arithmetic IF
is equivalent to multiple
This was the only conditional control statement in the original implementation of Fortran on the IBM 704
computer. On that computer it could be implemented quite efficiently using instructions such as 'Branch if accumulator negative'.
the conditional statement is not a language construct
but defined in the class
s.
var := condition
ifTrue: [ 'foo' ]
ifFalse: [ 'bar' ]
s (in some languages, case statements or multiway branches) compare a given value with specified constants and take action according to the first constant to match. There is usually a provision for a default action ('else','otherwise') to be taken if no match succeeds. Switch statements can allow compiler optimizations, such as lookup table
s. In dynamic languages, the cases may not be limited to constant expressions, and might extend to pattern matching
, as in the shell script
example on the right, where the '*)' implements the default case as a regular expression
matching any string.
may be seen as a more sophisticated alternative to both if-then-else, and case statements. It is available in many programming languages with functional programming features, such as ML and many others. Here is a simple example written in the Objective Caml
language:
match fruit with
| "apple" -> cook pie
| "coconut" -> cook dango_mochi
| "banana" -> mix;;
The power of pattern matching is the ability to concisely match not only actions but also values to patterns of data. Here is an example written in Haskell
which illustrates both of these features:
map _ [] = []
map f (h : t) = f h : map f t
This code defines a function map, which applies the first argument (a function) to each of the elements of the second argument (a list), and returns the resulting list. The two lines are the two definitions of the function for the two kinds of arguments possible in this case - one where the list is empty (just return an empty list) and the other case where the list is not empty.
Pattern matching is not strictly speaking always a choice construct, because it is possible in Haskell to write only one alternative, which is guaranteed to always be matched - in this situation, it is not being used as a choice construct, but simply as a way to bind names to values. However, it is frequently used as a choice construct in the languages in which it is available.
, branch predication
is a feature of certain central processing unit
(CPU) instruction sets which permits conditional execution of instructions, without having to perform costly conditional jumps.
Computer science
Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...
, conditional statements, conditional expressions and conditional constructs are features of 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....
which perform different computations or actions depending on whether a programmer-specified boolean
Boolean datatype
In computer science, the Boolean or logical data type is a data type, having two values , intended to represent the truth values of logic and Boolean algebra...
condition evaluates to true or false. Apart from the case of branch predication
Branch predication
Branch predication is a strategy in computer architecture design for mitigating the costs usually associated with conditional branches, particularly branches to short sections of code...
, this is always achieved by selectively altering the control flow
Control flow
In computer science, control flow refers to the order in which the individual statements, instructions, or function calls of an imperative or a declarative program are executed or evaluated....
based on some condition.
In imperative programming
Imperative programming
In computer science, imperative programming is a programming paradigm that describes computation in terms of statements that change a program state...
languages, the term "conditional 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...
" is usually used, whereas in functional programming
Functional programming
In computer science, functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data. It emphasizes the application of functions, in contrast to the imperative programming style, which emphasizes changes in state...
, the terms "conditional expression
Expression (programming)
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 another value...
" or "conditional construct" are preferred, because these terms all have distinct meanings.
Although dynamic dispatch
Dynamic dispatch
In computer science, dynamic dispatch is the process of mapping a message to a specific sequence of code at runtime. This is done to support the cases where the appropriate method can't be determined at compile-time...
is not usually classified as a conditional construct, it is another way to select between alternatives at runtime.
If-then(-else)
Theif-then construct (sometimes called if-then-else) is common across many programming languages. Although the syntax varies quite a bit from language to language, the basic structure (in pseudocodePseudocode
In computer science and numerical computation, pseudocode is a compact and informal high-level description of the operating principle of a computer program or other algorithm. It uses the structural conventions of a programming language, but is intended for human reading rather than machine reading...
form) looks like this: (The example is actually perfectly valid Visual Basic or QuickBASIC syntax.)
If (predicate)
Then
(consequent)
Else
(alternative)
End If
When an interpreter
Interpreter (computing)
In computer science, an interpreter normally means a computer program that executes, i.e. performs, instructions written in a programming language...
finds an
If, it expects a booleanBoolean datatype
In computer science, the Boolean or logical data type is a data type, having two values , intended to represent the truth values of logic and Boolean algebra...
condition - for example,
x > 0, which means "the variable x contains a number that is greater than zero" - and evaluates that condition. If the condition is true, the statements following the Then are executed. Otherwise, the execution continues in the following branch - either in the Else block (which is usually optional), or if there is no Else branch, then after the End If.After either branch has been executed, control
Control flow
In computer science, control flow refers to the order in which the individual statements, instructions, or function calls of an imperative or a declarative program are executed or evaluated....
returns to the point after the
End If.In early programming languages, especially some dialects of BASIC
BASIC
BASIC is a family of general-purpose, high-level programming languages whose design philosophy emphasizes ease of use - the name is an acronym from Beginner's All-purpose Symbolic Instruction Code....
in the 1980s home computer
Home computer
Home computers were a class of microcomputers entering the market in 1977, and becoming increasingly common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a single nontechnical user...
s, an
if-then statement could only contain GOTOGotogoto is a statement found in many computer programming languages. It is a combination of the English words go and to. It performs a one-way transfer of control to another line of code; in contrast a function call normally returns control...
statements. This led to a hard-to-read style of programming known as spaghetti programming, with programs in this style called spaghetti code. As a result, so called structured programmingStructured programming
Structured programming is a programming paradigm aimed on improving the clarity, quality, and development time of a computer program by making extensive use of subroutines, block structures and for and while loops - in contrast to using simple tests and jumps such as the goto statement which could...
which allows (virtually) arbitrary statements to be put in statement blocks inside an
if statement, gained in popularity, until it became the norm even in most BASIC programming circles. Such mechanisms and principles were based on the older but more advanced ALGOLALGOL
ALGOL is a family of imperative computer programming languages originally developed in the mid 1950s which greatly influenced many other languages and became the de facto way algorithms were described in textbooks and academic works for almost the next 30 years...
family of languages, and ALGOL-like languages such as Pascal
Pascal (programming language)
Pascal is an influential imperative and procedural programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small and efficient language intended to encourage good programming practices using structured programming and data structuring.A derivative known as Object Pascal...
and Modula-2
Modula-2
Modula-2 is a computer programming language designed and developed between 1977 and 1980 by Niklaus Wirth at ETH Zurich as a revision of Pascal to serve as the sole programming language for the operating system and application software for the personal workstation Lilith...
influenced modern BASIC variants for many years. While it is possible while using only
GOTO statements in if-then statements to write programs that are not spaghetti code and are just as well structured and readable as programs written in a structured programming language, so called structured programming makes this easier and enforces it. Structured if-then-else statements like the example above are one of the key elements of structured programming, and they are present in most popular high-level programming languages including CC (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....
, its derivatives (including C++
C++
C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
and C#), Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
, JavaScript
JavaScript
JavaScript is a prototype-based scripting language that is dynamic, weakly typed and has first-class functions. It is a multi-paradigm language, supporting object-oriented, imperative, and functional programming styles....
and Visual Basic
Visual Basic
Visual Basic is the third-generation event-driven programming language and integrated development environment from Microsoft for its COM programming model...
(all versions including .NET).
Else if
By usingElse If, it is possible to combine several conditions. Only the statements following the first condition that is found to be true will be executed. All other statements will be skipped. The statements of the final Else will be executed if none of the conditions are true. This example is written in the AdaAda (programming language)
Ada is a structured, statically typed, imperative, wide-spectrum, and object-oriented high-level computer programming language, extended from Pascal and other languages...
language:
if condition then
-- statements;
elsif condition then
-- more statements
elsif condition then
-- more statements;
...
else
-- other statements;
end if;
elsif, in Ada, is simply syntactic sugarSyntactic sugar
Syntactic sugar is a computer science term that refers to syntax within a programming language that is designed to make things easier to read or to express....
for
else followed by if. In Ada, the difference is that only one end if is needed, if one uses elsif instead of else followed by if.In some other languages, such as 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 Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
,
else if literally just means else followed by if, and syntactic sugar is neither needed nor provided. This works because in these languages, an else followed by one statement (in this case the if) does not need braces. This is not true in PerlPerl
Perl is a high-level, general-purpose, interpreted, dynamic programming language. Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions and become widely popular...
, which provides the keyword
elsif to avoid the large number of braces that would be required by multiple if and else statements. Similarly, PythonPython (programming language)
Python is a general-purpose, high-level programming language whose design philosophy emphasizes code readability. Python claims to "[combine] remarkable power with very clear syntax", and its standard library is large and comprehensive...
uses the special keyword
elif because structure is denoted by indentation rather than braces, so a repeated use of else and if would require increased indentation after every condition.C and Java implementations, however, do have a disadvantage that each
else if branch is, effectively, adding an extra nesting level, which will complicate compiler's writer job if arbitrarily long else if chains are to be supported.If expressions
Many languages support if expressions, which are similar to if statements, but return a value as a result. Thus, they are true expressions (which evaluate to a value), not statements (which just perform an action).As a ternary operator
In CC (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 C-like languages conditional expressions take the form of a ternary operator called the conditional expression operator, ?:
?:
In computer programming, ?: is a ternary operator that is part of the syntax for a basic conditional expression in several programming languages...
, which follows this template:
(condition)?(evaluate if condition was true):(evaluate if condition was false)
This means that conditions can be inlined into expressions, unlike with if statements, as shown here using C syntax:
//Invalid in most programming languages. One of exceptions is Ruby
my_variable = if(x > 10) { "foo" } else { "bar" };
//Valid
my_variable = (x > 10)?"foo":"bar";
To accomplish the same as the second (correct) line above, using a standard if/else statement, this would take more than one line of code (under standard layout conventions):
if (x > 10)
my_variable = 'foo';
else
my_variable = 'bar';
ALGOL 60
ALGOL 60
ALGOL 60 is a member of the ALGOL family of computer programming languages. It gave rise to many other programming languages, including BCPL, B, Pascal, Simula, C, and many others. ALGOL 58 introduced code blocks and the begin and end pairs for delimiting them...
and some other members of the ALGOL
ALGOL
ALGOL is a family of imperative computer programming languages originally developed in the mid 1950s which greatly influenced many other languages and became the de facto way algorithms were described in textbooks and academic works for almost the next 30 years...
family have the
if expression which performs the same function.In ALGOL:
myvariable := if x > 10 then 1 else 2
In the Lisp dialects Scheme and Common Lisp
Common Lisp
Common Lisp, commonly abbreviated CL, is a dialect of the Lisp programming language, published in ANSI standard document ANSI INCITS 226-1994 , . From the ANSI Common Lisp standard the Common Lisp HyperSpec has been derived for use with web browsers...
, the former of which was inspired to a great extent by ALGOL:
;; Scheme
(define myvariable (if (> x 10) 1 2)) ; Assigns ‘myvariable’ to 1 or 2, depending on the value of ‘x’
;; Common Lisp
(let ((x 5))
(setq myvariable (if (> x 10) 1 2))) ; Assigns ‘myvariable’ to 2
As a function
In Visual BasicVisual Basic
Visual Basic is the third-generation event-driven programming language and integrated development environment from Microsoft for its COM programming model...
and some other languages, a function called
IIfIIfIn computing, IIf is a function in several editions of the Visual Basic programming language, related languages such as ColdFusion Markup Language , and on spreadsheets that returns one of its three parameters based on the evaluation of one of the other parameters...
is provided, which can be used as a conditional expression. However, it does not behave like a true conditional expression, because both the true and false branches are always evaluated; it is just that the result of one of them is thrown away, while the result of the other is returned by the IIf function.In Haskell
In HaskellHaskell (programming language)
Haskell is a standardized, general-purpose purely functional programming language, with non-strict semantics and strong static typing. It is named after logician Haskell Curry. In Haskell, "a function is a first-class citizen" of the programming language. As a functional programming language, the...
98, there is only an if expression, no if statement, and the
else part is compulsory, as every expression must have some value. Logic that would be expressed with conditionals in other languages is usually expressed with pattern matchingPattern matching
In computer science, pattern matching is the act of checking some sequence of tokens for the presence of the constituents of some pattern. In contrast to pattern recognition, the match usually has to be exact. The patterns generally have the form of either sequences or tree structures...
in recursive functions.
Because Haskell is lazy
Lazy evaluation
In programming language theory, lazy evaluation or call-by-need is an evaluation strategy which delays the evaluation of an expression until the value of this is actually required and which also avoids repeated evaluations...
, it is possible to write control structures,. such as if, as ordinary expressions; the lazy evaluation means that an if function can evaluate only the condition and proper branch (where a strict language would evaluate all three). It can be written like this:
if' :: Bool -> a -> a -> a
if' True x _ = x
if' False _ y = y
Arithmetic if
Up to Fortran 77, the language Fortran has an "arithmetic if" statement which is halfway between a computed IF and a case statement, based on the trichotomy, , . This was the earliest conditional statement in Fortran. :IF (e) label1, label2, label3
Where e is any numeric expression (not necessarily an integer); this is equivalent to
IF (e .LT. 0) GOTO label1
IF (e .EQ. 0) GOTO label2
IF (e .GT. 0) GOTO label3
Because this arithmetic IF
Arithmetic IF
The arithmetic IF statement has been for several decades a three-way arithmetic conditional statement, starting from the very early version of Fortran, and including FORTRAN IV, FORTRAN 66 and FORTRAN 77...
is equivalent to multiple
GOTO statements, it is considered to be an unstructured control statement, and should not be used if more structured statements can be used. In practice it has been observed that most arithmetic IF statements referenced the following statement with one or two of the labels.This was the only conditional control statement in the original implementation of Fortran on the IBM 704
IBM 704
The IBM 704, the first mass-produced computer with floating point arithmetic hardware, was introduced by IBM in 1954. The 704 was significantly improved over the IBM 701 in terms of architecture as well as implementations which were not compatible with its predecessor.Changes from the 701 included...
computer. On that computer it could be implemented quite efficiently using instructions such as 'Branch if accumulator negative'.
Object-oriented implementation in Smalltalk
In contrast to other languages, in SmalltalkSmalltalk
Smalltalk is an object-oriented, dynamically typed, reflective programming language. Smalltalk was created as the language to underpin the "new world" of computing exemplified by "human–computer symbiosis." It was designed and created in part for educational use, more so for constructionist...
the conditional statement is not a language construct
Language construct
A language construct is a syntactically allowable part of a program that may be formed from one or more lexical tokens in accordance with the rules of a programming language....
but defined in the class
Boolean as an abstract method that takes two parameters, both closureClosure
Closure may refer to:* Closure used to seal a bottle, jug, jar, can, or other container** Closure , a stopper* Closure , the process by which an organization ceases operations...
s.
Boolean has two subclasses, True and False, which both define the method, True executing the first closure only, False executing the second closure only.var := condition
ifTrue: [ 'foo' ]
ifFalse: [ 'bar' ]
Case and switch statements
Switch statementSwitch statement
In computer programming, a switch, case, select or inspect statement is a type of selection control mechanism that exists in most imperative programming languages such as Pascal, Ada, C/C++, C#, Java, and so on. It is also included in several other types of languages...
s (in some languages, case statements or multiway branches) compare a given value with specified constants and take action according to the first constant to match. There is usually a provision for a default action ('else','otherwise') to be taken if no match succeeds. Switch statements can allow compiler optimizations, such as lookup table
Lookup table
In computer science, a lookup table is a data structure, usually an array or associative array, often used to replace a runtime computation with a simpler array indexing operation. The savings in terms of processing time can be significant, since retrieving a value from memory is often faster than...
s. In dynamic languages, the cases may not be limited to constant expressions, and might extend to pattern matching
Pattern matching
In computer science, pattern matching is the act of checking some sequence of tokens for the presence of the constituents of some pattern. In contrast to pattern recognition, the match usually has to be exact. The patterns generally have the form of either sequences or tree structures...
, as in the shell script
Shell script
A shell script is a script written for the shell, or command line interpreter, of an operating system. It is often considered a simple domain-specific programming language...
example on the right, where the '*)' implements the default case as a regular expression
Regular expression
In computing, a regular expression provides a concise and flexible means for "matching" strings of text, such as particular characters, words, or patterns of characters. Abbreviations for "regular expression" include "regex" and "regexp"...
matching any string.
| Pascal Pascal (programming language) Pascal is an influential imperative and procedural programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small and efficient language intended to encourage good programming practices using structured programming and data structuring.A derivative known as Object Pascal... : |
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.... : |
Java Java (programming language) Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities... : |
Shell script Shell script A shell script is a script written for the shell, or command line interpreter, of an operating system. It is often considered a simple domain-specific programming language... : |
|---|---|---|---|
case someChar of 'a': actionOnA; 'x': actionOnX; 'y','z':actionOnYandZ; else actionOnNoMatch; end; |
switch (someChar) { case 'a': actionOnA; break; case 'x': actionOnX; break; case 'y': case 'z': actionOnYandZ; break; default: actionOnNoMatch; } |
switch (age) { case 1: System.out.printf("You're one."; break; case 2: System.out.printf("You're two."; break; case 3: System.out.printf("You're three."; break; case 4: System.out.printf("You're one."; break; default: System.out.printf("You're neither!"; break; } |
case $someChar in a) actionOnA; ;; x) actionOnX; ;; [yz]) actionOnYandZ; ;; *) actionOnNoMatch ;; esac |
Pattern matching
Pattern matchingPattern matching
In computer science, pattern matching is the act of checking some sequence of tokens for the presence of the constituents of some pattern. In contrast to pattern recognition, the match usually has to be exact. The patterns generally have the form of either sequences or tree structures...
may be seen as a more sophisticated alternative to both if-then-else, and case statements. It is available in many programming languages with functional programming features, such as ML and many others. Here is a simple example written in the Objective Caml
Objective Caml
OCaml , originally known as Objective Caml, is the main implementation of the Caml programming language, created by Xavier Leroy, Jérôme Vouillon, Damien Doligez, Didier Rémy and others in 1996...
language:
match fruit with
| "apple" -> cook pie
| "coconut" -> cook dango_mochi
| "banana" -> mix;;
The power of pattern matching is the ability to concisely match not only actions but also values to patterns of data. Here is an example written in Haskell
Haskell (programming language)
Haskell is a standardized, general-purpose purely functional programming language, with non-strict semantics and strong static typing. It is named after logician Haskell Curry. In Haskell, "a function is a first-class citizen" of the programming language. As a functional programming language, the...
which illustrates both of these features:
map _ [] = []
map f (h : t) = f h : map f t
This code defines a function map, which applies the first argument (a function) to each of the elements of the second argument (a list), and returns the resulting list. The two lines are the two definitions of the function for the two kinds of arguments possible in this case - one where the list is empty (just return an empty list) and the other case where the list is not empty.
Pattern matching is not strictly speaking always a choice construct, because it is possible in Haskell to write only one alternative, which is guaranteed to always be matched - in this situation, it is not being used as a choice construct, but simply as a way to bind names to values. However, it is frequently used as a choice construct in the languages in which it is available.
Branch predication
In assembly languageAssembly language
An assembly language is a low-level programming language for computers, microprocessors, microcontrollers, and other programmable devices. It implements a symbolic representation of the machine codes and other constants needed to program a given CPU architecture...
, branch predication
Branch predication
Branch predication is a strategy in computer architecture design for mitigating the costs usually associated with conditional branches, particularly branches to short sections of code...
is a feature of certain central processing unit
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
(CPU) instruction sets which permits conditional execution of instructions, without having to perform costly conditional jumps.
Choice system cross reference
This table refers to the most recent language specification of each language. For languages that do not have a specification, the latest officially released implementation is referred to.| 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.... |
Structured if | switch Switch statement In computer programming, a switch, case, select or inspect statement is a type of selection control mechanism that exists in most imperative programming languages such as Pascal, Ada, C/C++, C#, Java, and so on. It is also included in several other types of languages... /select/case |
Arithmetic if | Pattern matching | ||
|---|---|---|---|---|---|---|
| then | else | else-if | ||||
| Ada Ada (programming language) Ada is a structured, statically typed, imperative, wide-spectrum, and object-oriented high-level computer programming language, extended from Pascal and other languages... |
||||||
| C/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.... |
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| C# | ||||||
| Eiffel Eiffel (programming language) Eiffel is an ISO-standardized, object-oriented programming language designed by Bertrand Meyer and Eiffel Software. The design of the language is closely connected with the Eiffel programming method... |
||||||
| F# | ||||||
| Fortran Fortran Fortran is a general-purpose, procedural, imperative programming language that is especially suited to numeric computation and scientific computing... |
||||||
| Haskell Haskell (programming language) Haskell is a standardized, general-purpose purely functional programming language, with non-strict semantics and strong static typing. It is named after logician Haskell Curry. In Haskell, "a function is a first-class citizen" of the programming language. As a functional programming language, the... |
||||||
| Java Java (programming language) Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities... |
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| ECMAScript (JavaScript) ECMAScript ECMAScript is the scripting language standardized by Ecma International in the ECMA-262 specification and ISO/IEC 16262. The language is widely used for client-side scripting on the web, in the form of several well-known dialects such as JavaScript, JScript, and ActionScript.- History :JavaScript... |
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| Perl Perl Perl is a high-level, general-purpose, interpreted, dynamic programming language. Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions and become widely popular... |
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| PHP PHP PHP is a general-purpose server-side scripting language originally designed for web development to produce dynamic web pages. For this purpose, PHP code is embedded into the HTML source document and interpreted by a web server with a PHP processor module, which generates the web page document... |
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| Pascal, Delphi, Oberon, etc. Pascal (programming language) Pascal is an influential imperative and procedural programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small and efficient language intended to encourage good programming practices using structured programming and data structuring.A derivative known as Object Pascal... |
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| Python Python (programming language) Python is a general-purpose, high-level programming language whose design philosophy emphasizes code readability. Python claims to "[combine] remarkable power with very clear syntax", and its standard library is large and comprehensive... |
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| QuickBASIC QuickBASIC Microsoft QuickBASIC is an Integrated Development Environment and compiler for the BASIC programming language that was developed by Microsoft. QuickBASIC runs mainly on DOS, though there was a short-lived version for Mac OS... |
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| Ruby Ruby (programming language) Ruby is a dynamic, reflective, general-purpose object-oriented programming language that combines syntax inspired by Perl with Smalltalk-like features. Ruby originated in Japan during the mid-1990s and was first developed and designed by Yukihiro "Matz" Matsumoto... |
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| Visual Basic Visual Basic Visual Basic is the third-generation event-driven programming language and integrated development environment from Microsoft for its COM programming model... , classic |
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| Visual Basic .NET Visual Basic .NET Visual Basic .NET , is an object-oriented computer programming language that can be viewed as an evolution of the classic Visual Basic , which is implemented on the .NET Framework... |
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| Windows PowerShell Windows PowerShell Windows PowerShell is Microsoft's task automation framework, consisting of a command-line shell and associated scripting language built on top of, and integrated with the .NET Framework... |
- This refers to pattern matching as a distinct conditional construct in the programming language - as opposed to mere string pattern matching support, such as regular expressionRegular expressionIn computing, a regular expression provides a concise and flexible means for "matching" strings of text, such as particular characters, words, or patterns of characters. Abbreviations for "regular expression" include "regex" and "regexp"...
support.
- The often-encountered
else ifin the C family of languages, and in Haskell, is not a language feature but a set of nested and independent if then else statements combined with a particular source code layout. However, this also means that a distinct else-if construct is not really needed in these languages.
- In Haskell and F#, a separate constant choice construct is unneeded, because the same task can be done with pattern matching.
See also
- Branch (computer science)Branch (computer science)A branch is sequence of code in a computer program which is conditionally executed depending on whether the flow of control is altered or not . The term can be used when referring to programs in high level languages as well as program written in machine code or assembly language...
- Dynamic dispatchDynamic dispatchIn computer science, dynamic dispatch is the process of mapping a message to a specific sequence of code at runtime. This is done to support the cases where the appropriate method can't be determined at compile-time...
for another way to make execution choices - McCarthy FormalismMcCarthy FormalismIn computer science and recursion theory the McCarthy Formalism of computer scientist John McCarthy clarifies the notion of recursive functions by use of the IF-THEN-ELSE construction common to computer science, together with the four of the operators of primitive recursive functions: zero,...
for history and historical references - Named condition
External links
- Coding samples and links to user documentation in many languages: ActionScript, Assembly, Bash, BASIC, C, C++, C#, Excel, Fortran, Java, JavaScript, JSP, Objective-C, Pascal, Perl, PHP, Python, Ruby, Tcl, Velocity, Windows PowerShell, XSL/XSLT
- IF NOT (ActionScript 3.0) video