Conditional structures: Difference between revisions
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{{Control Structures}}
[[Category:Simple]]
[[Category:Flow control]]
;Task:
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);</syntaxhighlight>
====case expressions====
Using the same example above, we assume that the
<syntaxhighlight lang="ada">Result := (case Op is
Add => A + B,
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</syntaxhighlight>
Note: some websites (particularly [https://www.radford.edu/nokie/classes/320/abe/operators.html#:~:text=if%20and%20case-,Examples%3A,1%2C%20others%20%3D%3E%200)%3B this one]) contain a different variant of a case expression (<syntaxhighlight lang="ada">case Op of...</syntaxhighlight>). The Ada Reference Manual indicates this is incorrect, and we use the [http://www.ada-auth.org/standards/12rm/html/RM-4-5-7.html formal version] here.
===case with a default alternative===
<syntaxhighlight lang="ada">type Days is (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday);
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===case without a default===
When there is no '''when others''' clause, the compiler will complain about any uncovered alternative. This defends against a common reason for bugs in other languages.
I.e., the following code is
<syntaxhighlight lang="ada">case Today is
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end case;</syntaxhighlight>
The
<syntaxhighlight lang="ada">case Today is
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<syntaxhighlight lang="befunge">& #v_ "0",@ zero
> "X",@ non-zero</syntaxhighlight>
=={{header|Binary Lambda Calculus}}==
Lambda calculus has no conditional structures built in, but the standard representations of booleans can be seen to implement if-then-else: true = \then. \else. then, false = \then. \else. else, which correspond to BLC programs <code>00 00 110</code> and <code>00 00 10</code>.
=={{header|blz}}==
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// if condition is true var will be set to 1, else false.
int var = condition ? 1 : 2;
</syntaxhighlight>
=={{header|Curto}}==
===si-sino===
<syntaxhighlight lang="curto">( condición ) si ( sentencias si verdadero ) entonces
( condición ) si ( sentencias si verdadero ) sino ( sentencias si falso ) entonces</syntaxhighlight>
ejemplo:
<syntaxhighlight lang="curto">
: menor-que-diez ( n -- )
10 < si
." Menor que 10"
sino
." Mayor o igual a 10"
entonces ;
</syntaxhighlight>
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=={{header|EasyLang}}==
<syntaxhighlight
i = randint 10
if i mod 2 = 0
print i & " is divisible by 2"
elif i mod 3 = 0
print i & " is divisible by 3"
else
print i & " is not divisible by 2 or 3"
.
</syntaxhighlight>
=={{header|Efene}}==
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x::xs = x :: force xs
[] = []</syntaxhighlight>
=={{header|EMal}}==
<syntaxhighlight lang="emal">
int i = 19
^|if–then–else|^
if i > 18
writeLine("greater than 18")
else
writeLine("less or equal to 18")
end
^|else if|^
if i == 18 do writeLine("equal to 18")
else if i < 18 do writeLine("less than 18")
else do writeLine("greater than 18")
end
^|when expression: just like iif in Visual Basic|^
writeLine(when(i > 18, "greater than 18", "less or equal to 18"))
^|hash-based conditionals|^
Map dispatch = int%fun[
18 => <|writeLine("equal to 18"),
19 => <|writeLine("yeah, it's 19")]
if dispatch.has(i) do dispatch[i]() end
</syntaxhighlight>
{{out}}
<pre>
greater than 18
greater than 18
greater than 18
yeah, it's 19
</pre>
=={{header|Erlang}}==
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=={{header|J}}==
See [[Conditional Structures/J]]
=={{header|Jakt}}==
<syntaxhighlight lang="jakt">
fn main() {
let a = 5
let b = 3
// If/else/else-if
if a > b {
println("a > b")
} else if a < b {
println("a < b")
} else {
println("a = b")
}
// Match
match a {
(..5) => {
println("a < 5")
}
5 => {
println("a == 5")
}
else => {
println("a > 5")
}
}
// Or equivalently
println(match a {
(..5) => "a < 5"
5 => "a == 5"
else => "a > 5"
})
// Hash based
let primality = [
1: false
2: false
3: true
4: false
5: true
6: false
]
let a_is_prime = primality[a]
println("a_is_prime = {}", a_is_prime)
}
</syntaxhighlight>
=={{header|Java}}==
===if-then-else===
<syntaxhighlight lang="java">if (s.equals("Hello World")) {
foo();
} else if (s.equals("Bye World"))
bar(); // braces optional for one-liners
else {
deusEx();
}</syntaxhighlight>
Java also supports [[wp:Short-circuit_evaluation|short-circuit evaluation]]. So in a conditional like this:
<syntaxhighlight lang="java">if (obj != null && obj.foo()) {
aMethod();
}</syntaxhighlight>
<tt>obj.foo()</tt> will not be executed if <tt>obj != null</tt> returns false. It is possible to have conditionals without short circuit evaluation using the <tt>&</tt> and <tt>|</tt> operators (from [[Bitwise operations]]). So in this conditional:
<syntaxhighlight lang="java">if (obj != null & obj.foo()) {
aMethod();
}</syntaxhighlight>
You will get a null pointer exception if <tt>obj</tt> is null.
===ternary===
<syntaxhighlight lang="java">s.equals("Hello World") ? foo() : bar();</syntaxhighlight>
The ternary operator is an expression, and is most often used as such:
<syntaxhighlight lang="java">Object newValue = s.equals("Hello World") ? a : b;</syntaxhighlight>
===switch===
This structure will only work if the code being switched on evaluates to an integer or character. There is no switching on
<syntaxhighlight lang="java">switch (c) {
case 'a':
foo();
break;
case 'b':
bar();
default:
foobar();
}</syntaxhighlight>
This particular example can show the "fallthrough" behavior of a switch statement. If c is the character b, then bar() and foobar() will both be called. If c is the character a, only foo() will be called because of the break statement at the end of that case.
Also, the switch statement can be easily translated into an
<syntaxhighlight lang="java">if (c == 'a') {
foo();
} else if (c == 'b') {
bar();
foobar();
} else {
foobar();
}</syntaxhighlight>
Cases without breaks at the end require duplication of code for all cases underneath them until a break is found (like the else if block shown here).
===switch expressions===
{{works with|Java|14+}}
Switch statements can be expressions. They must be exhaustive, and return a value with the <tt>yield</tt> keyword.
<syntaxhighlight lang=“java”>int x = switch (c) {
case 'a':
foo();
yield 1;
case 'b':
bar();
default:
foobar();
yield 0;
}</syntaxhighlight>
There is also a new syntax, available for both statements and expressions, that does not use fallthrough:
<syntaxhighlight lang=“java”>int y = switch (c) {
case '1', '2' -> 1 // multiple cases can be on one line
default -> { // use a block for multiple statements
foobar();
yield 0;
}
}</syntaxhighlight>
=={{header|JavaScript}}==
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=={{header|langur}}==
If and switch
In the shortened forms, you dispense with the keywords (except the first one).
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===simple if===
<syntaxhighlight lang="langur">if .x > .y: break</syntaxhighlight>
===switch
Switch
Switch
<syntaxhighlight lang="langur">switch .x, .y, .z {
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}
case true: ...
# all are true
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}</syntaxhighlight>
===implicit fallthrough===
If a block of a switch
<syntaxhighlight lang="langur">
case true:
# implicit fallthrough
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===explicit fallthrough from anywhere===
A fallthrough statement is allowed anywhere within a switch
<syntaxhighlight lang="langur">switch .x {
case true:
if .y > 100 {
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}</syntaxhighlight>
===shortened form switch
A shortened form expects a single action expression per test and is more limited in other ways, as well (no explicit fallthrough, no alternate test expressions, no alternate logical operators). A default section is optional (null by default).
<syntaxhighlight lang="langur">
true: ... ; #
_, >= .z: ...; # .y >= .z
... ) # default</syntaxhighlight>
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=={{header|Ol}}==
if-then, the simplest conditional `if` primitive.
<syntaxhighlight lang="scheme">
(if (= (* 2 2) 4
(if (= (* 2 2) 6)
(print "if-then: should not be printed"))
; ==> if-then: equal
</syntaxhighlight>
if-then-else, the full conditional
<syntaxhighlight lang="scheme">
(if (= (* 2 2) 4
(print "if-then-else: non equal"))
; ==> if-then-else: equal
(if (= (* 2 2) 6)
(print "if-then-else: equal")
(print "if-then-else: non equal"))
; ==> if-then-else: non equal
</syntaxhighlight>
when and unless, the
<syntaxhighlight lang="scheme">
(
; ==> when: ..just do something..
; ==>
(unless (= (* 2 2) 6)
(print "unless: ..just do something..")
(print "unless: not equal"))
; ==> unless: ..just do something..
; ==> unless: not equal
</syntaxhighlight>
if-then-else, extended conditional `if` primitive.
<syntaxhighlight lang="scheme">
(if (= (* 2 2) 4)
(print "if-then-else*: equal")
else
(print "if-then-else*: ..just do something..")
(print "if-then-else*: non equal"))
; ==> if-then-else*: equal
(if (= (* 2 2) 4)
then
(print "if-then-else*: ..just do something..")
(print "if-then-else*: equal")
else
(print "if-then-else*: ..just do something..")
(print "if-then-else*: non equal"))
; ==> if-then-else*: ..just do something..
; ==> if-then-else*: equal
(if (= (* 2 2) 4) ; same as `when`
then
(print "if-then-else*: ..just do something..")
(print "if-then-else*: equal"))
; ==> if-then-else*: ..just do something..
; ==> if-then-else*: equal
</syntaxhighlight>
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<syntaxhighlight lang="scheme">
(case (* 2 2)
(3 ; exact number
(print "case: 3"))
(4 ; exact number
(print "case: 4"))
((5 6 7) ; list of numbers
(print "case: 5 or 6 or 7"))
(else
(print "case: i don't know")))
; ==> case: 4
; extended case with usable else
(case (* 2 2)
(3 ; exact number
(print "case: 3"))
(else => (lambda (num)
(print "case: real value is " num))))
; ==> case: real value is 4
(case (* 2 2)
(3 ; exact number
(print "case: 3"))
(else is num
(print "case: real value is " num)))
; ==> case: real value is 4
; extended case with vectors
(case ['selector 1 2 3]
(['case1 x y]
(print "case: case1 " x ", " y))
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(else
(print "case: i don't know")))
; ==>
</syntaxhighlight>
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...
END;</syntaxhighlight>
=={{header|Plain English}}==
Plain English only has one kind of conditional, called a "conditional".
<syntaxhighlight lang="text">If [a decider], [do something]; [do another thing].</syntaxhighlight>
The first parameter is a decider that returns yes or no. If the result was yes, all the other statements on the same line as the conditional will execute. Otherwise, execution continues immediately to the next line.
If the decider uses a negative word, the negative word is removed, the decider is done normally, and the result is reversed.
Conditionals may not go beyond 1 SLOC. Conditionals cannot be nested.
=={{header|Pop11}}==
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(<code>]'[</code>, pronounced "meta-literal" grants the property of <code>'</code> (pronounced "literal", <code>'</code> places the item following it on the stack and unconditionally branches over it) to the enclosing nest.)
See [[Flow-control structures#Quackery]] for a deeper dive into Quackery control flow.
=={{header|R}}==
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}}
</syntaxhighlight>
=={{header|RPL}}==
'''IF..THEN'''
'''IF''' <instruction(s)> '''THEN''' <instruction(s)> '''END'''
'''IF..THEN..ELSE'''
'''IF''' <instruction(s)> '''THEN''' <instruction(s)> '''ELSE''' <instruction(s)> '''END'''
Instructions between <code>IF</code> and <code>THEN</code> are not mandatory, but recommended for lisibility. The interpreter considers <code>IF</code> as a null word and performs branching when meeting the word <code>THEN</code>: if stack level 1 is not equal to zero, the instructions between <code>THEN</code> and <code>END</code> will be executed.
<code>IFT</code> and <code>IFTE</code> are stack-based conditonal structures. <code>IFT</code> evaluates the content of stack level 1 only if the content of stack level 2 is not zero, otherwise it is dropped. <code>IFTE</code> evaluates the content of stack level 1 if the content of stack level 2 is zero, otherwise if evaluates the content of stack level 2.
'''CASE..END'''
'''CASE'''
<instruction(s)> '''THEN''' <instruction(s)> '''END'''
<instruction(s)> '''THEN''' <instruction(s)> '''END'''
<span style="color:grey">@ as many branches as needed</span>
<instruction(s)> <span style="color:grey">@ default branch (optional)</span>
'''END'''
=={{header|Ruby}}==
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(else 'zero))</syntaxhighlight>
=={{header|SmallBASIC}}==
===if===
<syntaxhighlight lang="basic">
IF foo == 1
PRINT "one"
ELSEIF foo == 2
PRINT "two"
ELSE
PRINT "something else"
ENDIF
</syntaxhighlight>
===Inline if===
<syntaxhighlight lang="basic">ans = iff(x <= 5, 0, 10)</syntaxhighlight>
===select===
<syntaxhighlight lang="basic">
select case x
case 12
print "x is 12"
case 13,14,15
print "x is 13,14,or 15"
case iff(x <= 4, x, x + 1)
print "x <= 4"
case else
print "x is not <=4,12,13,14,15"
end select
</syntaxhighlight>
=={{header|Smalltalk}}==
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There are optional <code>elif</code> (else if) and <code>else</code> clauses.
<syntaxhighlight lang="sh">if test 4 -ge 6
elif test 4 -lt 6
else echo '4 compares not to 6'
fi</syntaxhighlight>
Line 7,887 ⟶ 8,115:
else
x * fac (Nat.drop x 1)</syntaxhighlight>
=={{header|Ursalang}}==
===if…then…else===
Ursalang has a single conditional construct, the familiar `if…then…else`.<syntaxhighlight lang="ursalang">
if energyLevel > 9000 { "That's impossible!!!" } else { "Ok, I guess" }
</syntaxhighlight>As in most C-like languages, conditionals can be chained:<syntaxhighlight>
if color == "red" { "aaaaaah!" }
else if color == "blue" { "oooooh!" }
else { "eeeeeeee!" }
</syntaxhighlight>
=={{header|V}}==
Line 8,413 ⟶ 8,651:
=={{header|Wren}}==
The ''if/else'' statement and the ''ternary operator (?:)'' are Wren's basic conditional structures though it can be argued that the ''&&'' and ''||'' operators, which do short-circuit evaluation, should be included under this heading as well.
<syntaxhighlight lang="
if (b) {
System.print(true)
| |||