Conditional structures: Difference between revisions
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=={{header|Fancy}}== |
=={{header|Fancy}}== |
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Fancy has no built-in conditional structures. It uses a combination of polymorphism and blockliterals (closures) to achieve the same thing (like Smalltalk). |
Fancy has no built-in conditional structures. It uses a combination of polymorphism and blockliterals (closures) to achieve the same thing (like Smalltalk). |
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===if:then:=== |
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<lang fancy>if: (x < y) then: { |
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"x < y!" println # will only execute this block if x < y |
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} |
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</lang> |
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===if:then:else::=== |
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<lang fancy>if: (x < y) then: { |
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"x < y!" println # will only execute this block if x < y |
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} else: { |
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"x not < y!" println |
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} |
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</lang> |
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===if_true:=== |
===if_true:=== |
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Revision as of 19:51, 3 October 2011
You are encouraged to solve this task according to the task description, using any language you may know.
These are examples of control structures. You may also be interested in:
This page lists the conditional structures offered by different programming languages. Common conditional structures are if-then-else and switch.
6502 Assembly
6502 Assembly has 8 conditional branch instructions; each instruction will test the appropriate flag and condition and jump between -128 and 127 bytes. To understand these conditional instructions, it is helpful to remember that the comparison instructions (CMP, CPX, CPY) set the flags as if a subtraction had occurred: <lang 6502asm> LDA #10 CMP #11</lang> Following these instructions, the accumulator will still hold 10 but the flags are set as if you had instructed the processor to perform 10 - 11. The result is -1, so the sign flag will be set, the zero flag will be cleared, the overflow flag will be cleared, and the carry flag will be set. <lang 6502asm> BNE ;Branch on Not Equal - branch when the zero flag is set BEQ ;Branch on EQual - branch when the zero flag is set. ;The zero flag is set when the result of an operation is zero
BMI ;Branch on MInus BPL ;Branch on PLus - branch when the sign flag is cleared/set. ;The sign flag is set when the result of an instruction is a negative number ;and cleared when the result is a positive number
BVS ;Branch on oVerflow Set BVC ;Branch on oVerflow Cleared - branch when the overflow flag is cleared/set. ;The overflow flag is set when the result of an addition/subtraction would ;result in a number larger than 127 or smaller than -128
BCS ;Branch on Carry Set BCC ;Branch on Carry Clear - branch when the carry flag is cleared/set. ;The carry flag is set when an addition produced a carry and when ;a subtraction produced a borrow and cleared if an addition/subtraction ;does not produce a carry/borrow. The carry flag also holds bits ;after shifts and rotates.</lang> In the following example, the branch will be taken if memory location Variable holds 200: <lang 6502asm> LDA #200 CMP Variable BEQ #3 ;if equal, skip ahead 3 bytes... CLC ;if unequal, continue executing instructions ADC #1 STA OtherVariable ; ...to here.</lang> Because you don't have to perform a comparison to set the flags, you can perform very fast checks in interative loops: <lang 6502asm> LDX #100 Loop: ...do something DEX BNE Loop</lang> This code will loop until X is zero. Most assemblers will figure out the correct offset for you if you use a label in place of the offset after a branch instruction, as in the above example.
ActionScript
- See JavaScript
Ada
if-then-else
<lang ada>type Restricted is range 1..10; My_Var : Restricted;
if My_Var = 5 then
-- do something
elsif My_Var > 5 then
-- do something
else
-- do something
end if;</lang>
case
<lang ada>type Days is (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday); Today : Days;
case Today in
when Saturday | Sunday =>
null;
when Monday =>
Compute_Starting_Balance;
when Friday =>
Compute_Ending_Balance;
when Others =>
Accumulate_Sales;
end case;</lang>
select
Select provides conditional acceptance of entry calls. Select can also be used to conditionally call an entry
Conditional Accept
<lang ada>select
accept first_entry; -- do something or accept second_entry; -- do something or terminate;
end select;</lang>
Conditional entry call
A selective entry call provides a way to time-out an entry call. Without the time-out the calling task will suspend until the entry call is accepted. <lang ada>select
My_Task.Start;
or
delay Timeout_Period;
end select;</lang> The entry Start on the task My_Task will be called. If My_Task accepts the entry call before the timer expires the timer is canceled. If the timeout expires before the entry call is accepted the entry call is canceled.
Aikido
Conditional Expressions
<lang aikido> var x = loggedin ? sessionid : -1
</lang>
if..elif..else
<lang aikido> if (value > 40) {
println ("OK")
} elif (value < 20) {
println ("FAILED")
} else {
println ("RETRY")
} </lang>
switch
<lang aikido> switch (arg) { case "-d": case "--debug":
debug = true break
case "-f":
force = true break
default:
throw "Unknown option " + arg
}
switch (value) { case > 40:
println ("OK")
break
case < 20:
println ("FAILED")
break
case in 50..59:
println ("WIERD")
// fall through
default:
println ("RETRY")
}
</lang>
Aime
If-elif-else
<lang aime>if (c1) {
// first condition is true...
} elif (c2) {
// second condition is true...
} elif (c3) {
// third condition is true...
} else {
// none was true...
}</lang>
ALGOL 68
See Conditional Structures/ALGOL 68
AmbientTalk
If-then-else
In AmbientTalk, if:then:else: is a keyworded message (as in Smalltalk). The first argument should be a boolean expression. The second and third arguments should be blocks (aka anonymous functions or thunks).
<lang ambienttalk> if: condition then: {
// condition is true...
} else: {
// condition is false...
} </lang>
IfTrue/IfFalse
One can also send a message to the boolean objects true and false:
<lang ambienttalk> condition.ifTrue: { /* condition is true... */ } ifFalse: { /* condition is false... */ } </lang>
AmigaE
IF-THEN-ELSE <lang amigae>IF condition
-> if condition is true...
ELSEIF condition2
-> else if condition2 is true...
ELSE
-> if all other conditions are not true...
ENDIF</lang>
or on one single line:
<lang amigae>IF condition THEN statement</lang>
Ternary IF THEN ELSE
The IF-THEN-ELSE can be used like ternary operator (?: in C) <lang amigae>DEF c c := IF condition THEN 78 ELSE 19</lang>
SELECT-CASE
<lang amigae>SELECT var
CASE n1 -> code CASE n2 -> code DEFAULT -> no one of the previous case...
ENDSELECT</lang>
Another version allows for ranges:
<lang amigae>SELECT max_possible_value OF var
CASE n1 -> code CASE n2 TO n3, n4 -> more CASE n5 TO n6, n7 TO n8 -> more... DEFAULT -> none of previous ones
ENDSELECT</lang>
The biggest among n1, n2 and so on, must be not bigger than max_possible_value.
AppleScript
if-then-else
<lang applescript>if myVar is "ok" then return true
set i to 0 if i is 0 then
return "zero"
else if i mod 2 is 0 then
return "even"
else
return "odd"
end if</lang>
AutoHotkey
if, else if, else
ternary if
while (looping if)
<lang AutoHotkey>; if
x = 1
If x
MsgBox, x is %x%
Else If x > 1
MsgBox, x is %x%
Else
MsgBox, x is %x%
- ternary if
x = 2 y = 1 var := x > y ? 2 : 3 MsgBox, % var
- while
While (A_Index < 3) {
MsgBox, %A_Index% is less than 3
}</lang>
AWK
Conditionals in awk are modelled after C: <lang awk>if(i<0) i=0; else i=42</lang> including the ternary conditional <lang awk>i=(i<0? 0: 42)</lang>
BASIC
if-then-else
Single line IF does not require END IF
<lang qbasic>IF x = 0 THEN doSomething IF x < 0 THEN doSomething ELSE doOtherThing</lang>
Multi-line IF:
<lang qbasic>IF x > 0 AND x < 10 THEN
'do stuff
ELSE IF x = 0 THEN
'do other stuff
ELSE
'do more stuff
END IF</lang>
Like in C, any non-zero value is interpreted as True:
<lang qbasic>IF aNumber THEN
'the number is not 0
ELSE
'the number is 0
END IF</lang>
select case
The condition in each case branch can be one or more constants or variables, a range or an expression.
<lang qbasic>SELECT CASE expression CASE 1
'do stuff
CASE 2, 3
'do other stuff
CASE 3.1 TO 9.9
'do this
CASE IS >= 10
'do that
CASE ELSE
'default case
END SELECT</lang>
Computed ON-GOTO
Older line-numbered BASICs had a mechanism for vectoring execution based on the contents of a numeric variable (a low-budget case statement).
ON V GOTO 120,150,150,170
or:
<lang basic>10 INPUT "Enter 1,2 or 3: ";v 20 GOTO v * 100 99 STOP 100 PRINT "Apple" 110 STOP 200 PRINT "Banana" 210 STOP 300 PRINT "Cherry" 310 STOP</lang>
Conditional loops
Some variants of basic support conditional loops:
<lang bbcbasic>10 REM while loop 20 L=0 30 WHILE L<5 40 PRINT L 50 L=L+1 60 WEND 70 REM repeat loop 80 L=1 90 REPEAT 100 PRINT L 110 L=L+1 120 UNTIL L>5</lang>
Befunge
Befunge only has one conditional structure which comes in two flavors: vertical IF ( | ) and horizontal IF ( _ ). Befunge only has two boolean commands, greater-than ( ` ) and not ( ! ). These snippets input a number and use the conditional operators to print a "0" if it is zero and an "X" otherwise.
<lang befunge>v > "X",@ non-zero > & |
> "0",@ zero</lang>
# is the skip command. It unconditionally skips one character, allowing a little flexibility in flow control.
<lang befunge>& #v_ "0",@ zero
> "X",@ non-zero</lang>
Brainf***
Brainf*** has two conditional jump instructions, [ and ]. the [ instruction jumps forward to the corresponding ] instruction if the value at the current memory cell is zero, while the ] instruction jumps back if the current memory cell is nonzero. Thus in the following sequence:
<lang bf>[.]</lang>
The . instruction will be skipped, while the following sequence
<lang bf>+[.]</lang>
will result in an infinite loop. Finally, in the following sequence
<lang bf>+[.-]</lang>
The . instruction will be executed once.
C
C++
Run-Time Control Structures
- See C
Compile-Time Control Structures
Preprocessor Techniques
- See C
Template metaprogramming
Selecting a type depending on a compile time condition
<lang cpp>template<bool Condition, typename ThenType, typename Elsetype> struct ifthenelse;
template<typename ThenType, typename ElseType> struct ifthenelse<true, ThenType, ElseType> {
typedef ThenType type;
};
template<typename ThenType, typename ElseType> struct ifthenelse<false, ThenType, ElseType> {
typedef ElseType type;
};
// example usage: select type based on size ifthenelse<INT_MAX == 32767, // 16 bit int?
long int, // in that case, we'll need a long int
int> // otherwise an int will do
::type myvar; // define variable myvar with that type</lang>
Clean
if
There are no then or else keyword in Clean. The second argument of if is the then-part, the third argument is the else-part. <lang clean>bool2int b = if b 1 0</lang>
case-of
<lang clean>case 6 * 7 of
42 -> "Correct" _ -> "Wrong" // default, matches anything</lang>
function alternatives
<lang clean>answer 42 = True answer _ = False</lang>
guards
<lang clean>answer x
| x == 42 = True | otherwise = False
case 6 * 7 of
n | n < 0 -> "Not even close" 42 -> "Correct" // no default, could result in a run-time error</lang>
Clojure
if-then-else
<lang clojure>(if (= 1 1) :yes :no) ; returns :yes
(if (= 1 2) :yes :no) ; returns :no
(if (= 1 2) :yes) ; returns nil</lang>
when
Similar to if, but body in an implicit do block allowing multiple statements. No facility for providing an else. when is defined as a macro.
<lang clojure>(when x
(print "hello") (println " world") 5) ; when x is logical true, prints "hello world" and returns 5; otherwise does nothing, returns nil</lang>
cond
The cond macro takes a series of test/result pairs, evaluating each test until one resolves to logical true, then evaluates its result. Returns nil if none of the tests yield true. <lang clojure>(cond
(= 1 2) :no) ; returns nil
(cond
(= 1 2) :no (= 1 1) :yes) ; returns :yes</lang>
Since non-nil objects are logical true, by convention the keyword :else is used to yield a default result. <lang clojure>(cond
(= 1 2) :no :else :yes) ; returns :yes</lang>
condp
Similar to cond, but useful when each test differs by only one variant. <lang clojure>(condp < 3
4 :a ; cond equivalent would be (< 4 3) :a 3 :b 2 :c 1 :d) ; returns :c</lang>
Optionally takes a final arg to be used as the default result if none of the tests match. <lang clojure>(condp < 3
4 :a 3 :b :no-match) ; returns :no-match</lang>
case
<lang clojure>(case 2
0 (println "0") 1 (println "1") 2 (println "2")) ; prints 2.</lang>
CMake
<lang cmake>set(num 5)
if(num GREATER 100)
message("${num} is very large!")
elseif(num GREATER 10)
message("${num} is large.")
else()
message("${num} is small.")
message("We might want a bigger number.")
endif()</lang>
The if() and elseif() commands evaluate boolean expressions like num GREATER 100; refer to cmake --help-command if. The elseif() and else() sections are optional.
COBOL
if-then-else
<lang cobol>if condition-1
imperative-statement-1
else
imperative-statement-2
end-if
if condition-1
if condition-a
imperative-statement-1a
else
imperative-statement-1
end-if
else
if condition-a
imperative-statement-2a
else
imperative-statement-2
end-if
end-if</lang>
evaluate
<lang cobol>evaluate identifier-1 when 'good'
good-imperative-statement
when 'bad'
bad-imperative-statement
when 'ugly' when 'awful'
ugly-or-awful-imperative-statement
when other
default-imperative-statement
end-evaluate
evaluate true when condition-1
condition-1-imperative-statement
when condition-2
condition-2-imperative-statement
when condition-3
condition-3-imperative-statement
when other
default-condition-imperative-statement
end-evaluate
evaluate identifier-1 also identifier-2 when 10 also 20
one-is-10-and-two-is-20-imperative-statement
when 11 also 30
one-is-11-and-two-is-30-imperative-statement
when 20 also any
one-is-20-and-two-is-anything-imperative-statement
when other
default-imperative-statement
end-evaluate</lang>
ColdFusion
if-elseif-else
Compiler: ColdFusion any version <lang cfm><cfif x eq 3>
do something
<cfelseif x eq 4>
do something else
<cfelse>
do something else
</cfif></lang>
switch
Compiler: ColdFusion any version <lang cfm><cfswitch expression="#x#">
<cfcase value="1"> do something </cfcase> <cfcase value="2"> do something </cfcase> <cfdefaultcase> do something </cfdefaultcase>
</cfswitch></lang>
Common Lisp
There are 2 main conditional operators in common lisp, (if ...) and (cond ...).
(if cond then [else])
The (if ...) construct takes a predicate as its first argument and evaluates it. Should the result be non-nil, it goes on to evaluate and returnm the results of the 'then' part, otherwise, when present, it evaluates and returns the result of the 'else' part. Should there be no 'else' part, it returns nil.
<lang lisp>(if (= val 42)
"That is the answer to life, the universe and everything" "Try again") ; the else clause here is optional</lang>
when and unless
Common Lisp also includes (when condition form*) and (unless condition form*) which are equivalent, respectively, to (if condition (progn form*)) and (if (not condition) (progn form*)).
It is unidiomatic to use if without an else branch for side effects; when should be used instead.
(cond (pred1 form1) [... (predN formN)])
The (cond ...) construct acts as both an if..elseif...elseif...else operator and a switch, returning the result of the form associated with the first non-nil predicate.
<lang lisp>(cond ((= val 1) (print "no"))
((and (> val 3) (< val 6)) (print "yes"))
((> val 99) (print "too far"))
(T (print "no way, man!")))</lang>
Crack
if-elseif-else
<lang crack>if (condition) {
// Some Task
}
if (condition) {
// Some Task
} else if (condition2) {
// Some Task
} else {
// Some Task
}</lang>
Ternary
<lang crack> // if condition is true var will be set to 1, else false. int var = condition ? 1 : 2; </lang>
C#
if-elseif-else
<lang csharp>if (condition) {
// Some Task
}
if (condition) {
// Some Task
} else if (condition2) {
// Some Task
} else {
// Some Task
}</lang>
Ternary
<lang csharp>// if condition is true var will be set to 1, else false. int var = condition ? 1 : 2;</lang>
switch
<lang csharp>switch (value) {
case 1:
// Some task
break; // Breaks are required in C#.
case 2:
case 3:
// Some task
break;
default: // If no other case is matched.
// Some task
break;
}</lang>
If fall through algorithms are required use the goto keyword.
<lang csharp>switch (value) {
case 1:
// Some task
goto case 2; // will cause the code indicated in case 2 to be executed.
case 2:
// Some task
break;
case 3:
// Some task
break;
default: // If no other case is matched.
// Some task
break;
}</lang>
D
- See C, sans the preprocessor.
Compile-time check: <lang d>const i = 5; static if (i == 7) { ... } else { ... }</lang>
Compile-time type check: <lang d> auto i = 5; // is(T: U) tests if T is implicitly castable to U. // typeof(var) is the type of the variable. // also: is(T==U) checks if T is U. static if (is(typeof(i) : int)) {
...
} else {
...
}</lang>
Dao
If Elif Else
<lang dao>a = 3 if( a == 1 ){
io.writeln( 'a == 1' )
}elif( a== 3 ){
io.writeln( 'a == 3' )
}else{
io.writeln( 'a is neither 1 nor 3' )
}</lang>
Switch Case
<lang dao>a = 3 switch( a ){ case 0: io.writeln( 'case 0' ) case 1, 2: io.writeln( 'case 1,2' ) case 3 ... 5: io.writeln( 'case 3...5' ) default: io.writeln( 'default' ) }</lang>
Deluge
<lang deluge>if (input.Field == "Hello World") {
sVar = "good";
} else if (input.Field == "Bye World") {
sVar = "bad";
} else {
sVar = "neutral";
}</lang>
Delphi
- See Pascal
DWScript
- See Pascal
E
if-then-else
<lang e>if (okay) {
println("okay")
} else if (!okay) {
println("not okay")
} else {
println("not my day")
}</lang>
The pick/2 message of booleans provides a value-based conditional:
<lang e>println(okay.pick("okay", "not okay"))</lang>
It can therefore be used to construct a Smalltalk-style conditional:
<lang e>okay.pick(fn {
println("okay")
}, fn {
println("not okay")
})()</lang>
All of the above conditionals are expressions and have a usable return value.
switch
E's "switch" allows pattern matching.
<lang e>def expression := ["+", [1, 2]]
def value := switch (expression) {
match [`+`, [a, b]] { a + b }
match [`*`, [a, b]] { a * b }
match [op, _] { throw(`unknown operator: $op`) }
}</lang>
Efene
the expressions can contain parenthesis or not, here both options are shown
since if and case do pattern matching if an if or case expression don't match some of the patterns the program will crash
<lang efene> show_if_with_parenthesis = fn (Num) {
if (Num == 1) {
io.format("is one~n")
}
else if (Num === 2) {
io.format("is two~n")
}
else {
io.format("not one not two~n")
}
}
show_if_without_parenthesis = fn (Num) {
if Num == 1 {
io.format("is one~n")
}
else if Num === 2 {
io.format("is two~n")
}
else {
io.format("not one not two~n")
}
}
show_switch_with_parenthesis = fn (Num) {
switch (Num) {
case (1) {
io.format("one!~n")
}
case (2) {
io.format("two!~n")
}
else {
io.format("else~n")
}
}
}
show_switch_without_parenthesis = fn (Num) {
switch (Num) {
case 1 {
io.format("one!~n")
}
case 2 {
io.format("two!~n")
}
else {
io.format("else~n")
}
}
}
@public run = fn () {
show_if_with_parenthesis(random.uniform(3)) show_if_without_parenthesis(random.uniform(3))
show_switch_with_parenthesis(random.uniform(3)) show_switch_without_parenthesis(random.uniform(3))
}</lang>
Ela
if-then-else
<lang ela>if x < 0 then 0 else x</lang>
Guards
<lang ela>let getX x | x < 0 = 0
| else = x</lang>
Pattern matching
<lang ela>let force (x::xs) = x :: force xs
force [] = []</lang>
match expression
<lang ela> let force lst = match lst with
x::xs = x :: force xs
[] = []</lang>
is expression
<lang ela> let force lst = if lst is (x::xs) then
x :: force xs
else []</lang>
Factor
There are many conditional structures in Factor. Here I'll demonstrate the most common ones. A few of these have other variations that abstract common stack shuffle patterns. I will not be demonstrating them.
?
? is for when you don't need branching, but only need to select between two different values. <lang factor> t 1 2 ? ! returns 1 </lang>
if
<lang factor>t [ 1 ] [ 2 ] if ! returns 1</lang>
cond
<lang factor>{ { [ t ] [ 1 ] } { [ f ] [ 2 ] } } cond ! returns 1</lang>
case
<lang factor>t { { t [ 1 ] } { f [ 2 ] } } case ! returns 1</lang>
when
<lang factor>t [ "1" print ] when ! prints 1</lang>
unless
<lang factor>f [ "1" print ] unless ! prints 1</lang>
FALSE
<lang false>condition[body]?</lang> Because there is no "else", you need to stash the condition if you want the same effect: <lang false>$[\true\]?~[false]?</lang> or <lang false>$[%true0~]?~[false]?</lang>
Fancy
Fancy has no built-in conditional structures. It uses a combination of polymorphism and blockliterals (closures) to achieve the same thing (like Smalltalk).
if:then:
<lang fancy>if: (x < y) then: {
"x < y!" println # will only execute this block if x < y
} </lang>
if:then:else::
<lang fancy>if: (x < y) then: {
"x < y!" println # will only execute this block if x < y
} else: {
"x not < y!" println
} </lang>
if_true:
<lang fancy>x < y if_true: {
"x < y!" println # will only execute this block if x < y
} </lang>
if_false: / if_nil:
<lang fancy>x < y if_false: {
"x not < y!" println # will only execute this block if x >= y
} </lang>
if_true:else:
<lang fancy>x < y if_true: {
"x < y!" println
} else: {
"x >= y!" println
} </lang>
if_false:else:
<lang fancy>x < y if_false: {
"x >= y!"
} else: {
"x < y!" println
} </lang>
if:
<lang fancy>{ "x < y!" println } if: (x < y) # analog, but postfix</lang>
unless:
<lang fancy>{ "x not < y!" } unless: (x < y) # same here</lang>
Forth
IF-ELSE
<lang forth>( condition ) IF ( true statements ) THEN ( condition ) IF ( true statements ) ELSE ( false statements ) THEN</lang> example: <lang forth>10 < IF ." Less than 10" ELSE ." Greater than or equal to 10" THEN</lang>
CASE-OF
<lang forth>( n -- ) CASE ( integer ) OF ( statements ) ENDOF ( integer ) OF ( statements ) ENDOF ( default instructions ) ENDCASE</lang> example: a simple CASE selection <lang forth>: test-case ( n -- )
CASE
0 OF ." Zero!" ENDOF
1 OF ." One!" ENDOF
." Some other number!"
ENDCASE ;</lang>
Execution vector
To obtain the efficiency of a C switch statement for enumerations, one needs to construct one's own execution vector. <lang forth>: switch
CREATE ( default-xt [count-xts] count -- ) DUP , 0 DO , LOOP , DOES> ( u -- ) TUCK @ MIN 1+ CELLS + @ EXECUTE ;
:NONAME ." Out of range!" ; :NONAME ." nine" ; :NONAME ." eight" ; :NONAME ." seven" ; :NONAME ." six" ; :NONAME ." five" ; :NONAME ." four" ; :NONAME ." three" ; :NONAME ." two" ; :NONAME ." one" ; :NONAME ." zero" ;
10 switch digit
8 digit \ eight
34 digit \ Out of range!</lang>
Fortran
In ISO Fortran 90 and later, there are three conditional structures. There are also a number of other *unstructured* conditional statements, all of which are old and many of which are marked as "deprecated" in modern Fortran standards. These examples will, as requested, only cover conditional *structures*:
IF-THEN-ELSE
ANSI FORTRAN 77 or later has an IF-THEN-ELSE structure: <lang fortran>if ( a .gt. 20.0 ) then
q = q + a**2
else if ( a .ge. 0.0 ) then
q = q + 2*a**3
else
q = q - a
end if</lang>
SELECT-CASE
ISO Fortran 90 or later has a SELECT-CASE structure: <lang fortran>select case (i)
case (21:) ! matches all integers greater than 20
q = q + i**2
case (0:20) ! matches all integers between 0 and 20 (inclusive)
q = q + 2*i**3
case default ! matches all other integers (negative in this particular case)
q = q - I
end select</lang>
WHERE-ELSEWHERE
ISO Fortran 90 and later has a concurrent, array-expression-based WHERE-ELSEWHERE structure. The logical expressions in WHERE and ELSEWHERE clauses must be array-values. All statements inside the structure blocks must be array-valued. Furthermore, all array-valued expressions and statements must have the same "shape". That is, they must have the same number of dimensions, and each expression/statement must have the same sizes in corresponding dimensions as each other expression/statement. For each block, wherever the logical expression is true, the corresponding elements of the array expressions/statements are evaluated/executed. <lang fortran>! diffusion grid time step where (edge_type(1:n,1:m) == center)
anew(1:n,1:m) = (a(1:n,1:m) + a(0:n-1,1:m) + a(2:n+1,1:m) + a(1:n,0:m-1) + a(1:n,2:m+1)) / 5
elsewhere (edge_type(1:n,1:m) == left)
anew(1:n,1:m) = (a(1:n,1:m) + 2*a(2:n+1,1:m) + a(1:n,0:m-1) + a(1:n,2:m+1)) / 5
elsewhere (edge_type(1:n,1:m) == right)
anew(1:n,1:m) = (a(1:n,1:m) + 2*a(0:n-1,1:m) + a(1:n,0:m-1) + a(1:n,2:m+1)) / 5
elsewhere (edge_type(1:n,1:m) == top)
anew(1:n,1:m) = (a(1:n,1:m) + a(0:n-1,1:m) + a(2:n+1,1:m) + 2*a(1:n,2:m+1)) / 5
elsewhere (edge_type(1:n,1:m) == bottom)
anew(1:n,1:m) = (a(1:n,1:m) + a(0:n-1,1:m) + a(2:n+1,1:m) + 2*a(1:n,0:m-1)) / 5
elsewhere (edge_type(1:n,1:m) == left_top)
anew(1:n,1:m) = (a(1:n,1:m) + 2*a(2:n+1,1:m) + 2*a(1:n,2:m+1)) / 5
elsewhere (edge_type(1:n,1:m) == right_top)
anew(1:n,1:m) = (a(1:n,1:m) + 2*a(0:n-1,1:m) + 2*a(1:n,2:m+1)) / 5
elsewhere (edge_type(1:n,1:m) == left_bottom)
anew(1:n,1:m) = (a(1:n,1:m) + 2*a(2:n+1,1:m) + 2*a(1:n,0:m-1)) / 5
elsewhere (edge_type(1:n,1:m) == right_bottom)
anew(1:n,1:m) = (a(1:n,1:m) + 2*a(0:n-1,1:m) + 2*a(1:n,0:m-1)) / 5
elsewhere ! sink/source, does not change
anew(1:n,1:m) = a(1:n,1:m)
end where</lang>
Go
If and switch are the general purpose conditional structures in Go, although the language certainly contains other conditional elements.
If
Simplest usage is, <lang go>if booleanExpression {
statements
}</lang> The braces are required, even around a single statement. <lang go>if booleanExpression {
statements
} else {
other statements
}</lang> The above shows the idiomatic way to write an if/else. If the else clause contains only a single statement however, it is legal to leave off the braces around that single statement, as in, <lang go>if booleanExpression {
statements
} else singleStatement</lang> Since an if statement is a statment, chains of if/else if statements can be written like this: <lang go>if booleanExpression1 {
statements
} else if booleanExpression2 {
otherStatements
} </lang> Neither of the last two examples are "best practice" however. In the first case, it is common to put braces around the single statement anyway. In the second case, a select statement is preferred.
If allows a statement to be included ahead of the condition. This is commonly a short variable declaration, as in, <lang go>if x := fetchSomething(); if x > 0 {
DoPos(x)
} else {
DoNeg(x)
}</lang> In this case the scope of x is limited to if statement.
Switch
Simple usage is, <lang go>switch { case booleanExpression1:
statements
case booleanExpression2:
other statements
default:
last resort statements
}</lang> Because switch can work with any number of arbitrary boolean expressions, it replaces if/elseif chains often found in other programming languages.
Switch can also switch on the value of an expression, as in, <lang go>switch expressionOfAnyType { case value1:
statements
case value2, value3, value4:
other statements
}</lang> As shown, multiple values can be listed for a single case clause. Since go is statically typed, the types of value1, 2, 3, and 4 must match the type of the expression.
As with if, a local statement such as a short variable declaration can precede the expression. If there is no expression, the statement is still marked by a semicolon: <lang go>switch x := fetch(); { case x == "cheese":
statements
case otherBooleanExpression:
other statements
}</lang> Also, as with if, the scope of x is limited to the switch statement.
Execution does not normally fall through from one case clause to the next, but this behavior can be forced with a fallthrough statement.
An interesting example: <lang go>switch { case booleanExpression1: default:
statements preliminaryToOtherStatements fallthrough
case booleanExpression2:
other statements
}</lang> Case expressions are evaluated in order, then if none are true, the default clause is executed.
Another statement that interacts with switch is break. It breaks from the switch statement and so will not break from a surrounding for statement. The following example prints "I want out!" endlessly. <lang go>for {
switch {
case true:
break
}
fmt.Println("I want out!")
}</lang> Labels provide the desired capability. The following prints "I'm off!" <lang go>treadmill: for {
switch {
case true:
break treadmill
}
} fmt.Println("I'm off!")</lang>
Haskell
if-then-else
<lang haskell>fac x = if x==0 then
1
else x * fac (x - 1)</lang>
Guards
<lang haskell>fac x | x==0 = 1
| x>0 = x * fac (x-1)</lang>
Pattern matching
<lang haskell>fac 0 = 1 fac x = x * fac (x-1)</lang>
case statement
<lang haskell>fac x = case x of 0 -> 1
_ -> x * fac (x-1)</lang>
HicEst
<lang hicest>IF( a > 5 ) WRITE(Messagebox) a ! single line IF
IF( a >= b ) THEN
WRITE(Text=some_string) a, b ELSEIF(some_string > "?") THEN WRITE(ClipBoard) some_string ELSEIF( nonzero ) THEN WRITE(WINdowhandle=nnn) some_string ELSE WRITE(StatusBar) a, b, some_string
ENDIF</lang>
IDL
if-else
Basic if/then:
<lang idl>if a eq 5 then print, "a equals five" [else print, "a is something else"]</lang>
Any one statement (like these print statements) can always be expanded into a {begin ... end} pair with any amount of code in between. Thus the above will expand like this:
<lang idl>if a eq 5 then begin
... some code here ...
endif [else begin
... some other code here ...
endelse]</lang>
case
<lang idl>case <expression> of
(choice-1): <command-1> [(choice-2): <command-2> [...]] [else: <command-else>]
endcase</lang>
(Or replace any of the commands with {begin..end} pairs)
switch
<lang idl>switch <expression> of
(choice-1): <command-1> [(choice-2): <command-2> [...]] [else: <command-else>]
endswitch</lang>
The switch will execute all commands starting with the matching result, while the case will only execute the matching one.
on_error
<lang idl>on_error label</lang>
Will resume execution at label when an error is encountered. on_ioerror is similar but for IO errors.
Icon and Unicon
All Icon and Unicon expressions, including control structures, yield results or signal failure.
if-then-else
The control structure evaluates expr1 if expr0 succeeds and expr2 if it fails. <lang Icon>if expr0 then
expr1
else
expr2</lang>
case-of
The first successful selection expression will select and evaluate the specific case. <lang Icon>case expr0 of {
expr1 : expr2 expr3 : expr4 default: expr5 }</lang>
Note that expr1 and expr3 are expressions and not constants and it is possible to write expressions such as: <lang Icon>case x of {
f(x) | g(x) : expr2 s(x) & t(x) : expr4 default: expr5 }</lang>
Compound expressions (blocks)
In the examples below, multiple expressions can be grouped as in: <lang Icon>{
expr1 expr2 expr3
}</lang> Which is equivalent to this: <lang Icon>{expr1; expr2; expr3}</lang> For example the following, which will write 4, looks strange but is valid: <lang Icon>write({1;2;3;4})</lang> The value of a compound expression is the value of the last expression in the block.
Alternation
Alternation of expressions yields a value for the first succeeding expression. <lang Icon> expr1 | expr2 | expr3</lang>
Conjunction
Conjunctions yeild the value of the final expression provided all the previous expressions succeed. <lang Icon> expr1 & expr2 & expr3</lang> Alternately, conjunction can be written thus: <lang Icon> (expr1, expr2, expr3)</lang>
Conjunction, yielding a different result
The alternate form of conjunction can be modified to produce a different result (other than the last)
<lang Icon> expr0(expr1, expr2, expr3)</lang>
For example:
<lang Icon> 2(expr1, expr2, expr3)</lang>
Yields the value of expr2 if all of the expressions succeed.
A more complicated example showing non-constant expressions:
<lang Icon> f(expr1)(g(expr2)(expr3,expr4,expr5))</lang>
Note: if expr0 yields a value of type 'procedure' or 'string' the appropriate procedure (or operator) is invoked.
Inform 7
if-then-else
<lang inform7>[short form] if N is 1, say "one."; otherwise say "not one.";
[block form] if N is 1: say "one."; otherwise if N is 2: say "two."; otherwise: say "not one or two.";
[short and long forms can be negated with "unless"] unless N is 1, say "not one."</lang>
switch
<lang inform7>if N is: -- 1: say "one."; -- 2: say "two."; -- otherwise: say "not one or two.";</lang>
if-then-else in text
<lang inform7>say "[if N is 1]one[otherwise if N is 2]two[otherwise]three[end if]."; say "[unless N is odd]even.[end if]";</lang>
other branching text substitutions
Text that may be printed multiple times can also use sequential and random branching: <lang inform7>[a different color every time] say "[one of]red[or]blue[or]green[at random].";
["one" the first time it's printed, "two" the second time, then "three or more" subsequently] say "[one of]one[or]two[or]three or more[stopping]";
[only appears once] say "[first time]Hello world![only]";</lang>
rulebook approach
Conditional logic may also be expressed in the form of a rulebook, with conditions on each rule:
<lang inform7>Number Factory is a room.
Number handling is a number based rulebook with default success.
Number handling for 1: say "one." Number handling for 2: say "two." Number handling for an even number (called N): say "[N in words] (which is even)." Last number handling rule: say "other."
When play begins: follow the number handling rules for 2; follow the number handling rules for 4; follow the number handling rules for 5.</lang>
J
Java
if-then-else
<lang java>if(s.equals("Hello World")) {
foo();
} else if(s.equals("Bye World"))
bar();//{}'s optional for one-liners
else {
deusEx();
}</lang> Java also supports short-circuit evaluation. So in a conditional like this: <lang java>if(obj != null && obj.foo()){
aMethod();
}</lang> obj.foo() will not be executed if obj != null returns false. It is possible to have conditionals without short circuit evaluation using the & and | operators (from Bitwise operations). So in this conditional: <lang java>if(obj != null & obj.foo()){
aMethod();
}</lang> You will get a null pointer exception if obj is null.
ternary
<lang java>s.equals("Hello World") ? foo() : bar();</lang>
switch
This structure will only work if the code being switched on evaluates to an integer or character. There is no switching on Objects or floating-point types in Java (except for Strings in Java 7 and higher).
<lang java>switch(c) {
case 'a':
foo(); break;
case 'b':
bar();
default:
foobar();
}</lang> 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 if-else if-else statement. The example above is equivalent to: <lang java>if(c == 'a'){
foo();
}else if(c == 'b'){
bar(); foobar();
}else{
foobar();
}</lang> 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).
JavaScript
if-then-else
<lang javascript>if( s == "Hello World" ) {
foo();
} else if( s == "Bye World" ) {
bar();
} else {
deusEx();
}</lang>
switch
<lang javascript>switch(object) {
case 1:
one();
break;
case 2:
case 3:
case 4:
twoThreeOrFour();
break;
case 5:
five();
break;
default:
everythingElse();
}</lang>
conditional (ternary) operator (?:)
<lang javascript>var num = window.obj ? obj.getNumber() : null;</lang>
Lisaac
if-then-else
<lang Lisaac>+ n : INTEGER;
n := 3;
(n = 2).if {
IO.put_string "n is 2\n";
}.elseif {n = 3} then {
IO.put_string "n is 3\n";
}.elseif {n = 4} then {
IO.put_string "n is 4\n";
} else {
IO.put_string "n is none of the above\n";
};</lang> <lang Lisaac>(n = 2).if_true { "n is 2\n".print; }; (n = 2).if_false { "n is not 2\n".print; };</lang>
when
<lang Lisaac>+ n : INTEGER;
n := 3; n .when 2 then {
"n is 2\n".print;
} .when 3 then {
"n is 3\n".print;
} .when 4 then {
"n is 4\n".print;
};</lang> There is no "else" or "otherwise" method. If the values of the when-methods are overlapped, the related blocks will be evaluated ... they are not mutually exclusive.
Logo
<lang logo>if :x < 0 [make "x 0 - :x]
ifelse emptyp :list [print [empty]] [print :list]</lang> UCBLogo and its descendants have also case: <lang logo>to vowel? :letter output case :letter [ [[a e i o u] "true] [else "false] ] end show vowel? "e show vowel? "x</lang> Output is: <lang logo>true false</lang> Logo also provides TEST which is local to a procedure: <lang logo>to mytest :arg1 :arg2 test :arg1 = :arg2 iftrue [print [Arguments are equal]] iffalse [print [Arguments are not equal]] end</lang>
LSE64
The simple conditionals take single words rather than blocks of statements, as in most other languages. <lang lse64>t : " true" ,t f : " false" ,t true if t false ifnot f true ifelse t f</lang>
Cascading conditionals are constructed using duplicate definitions and "then", yielding a syntax reminiscent of functional language Pattern Matching. <lang lse64>onetwo : drop " Neither one nor two" ,t # default declared first onetwo : dup 2 = then " Two" ,t onetwo : dup 1 = then " One" ,t</lang>
Short-circuit operators "&&" and "||" are used for complex conditionals. <lang lse64>dup 0 = || ,t # avoid printing a null string</lang>
Lua
<lang Lua> --if-then-elseif-then-else if a then
b()
elseif c then
d()
else
e()
end
for var = start, _end, step do --note: end is a reserved word
something()
end
for var, var2, etc in iteratorfunction do
something()
end
while somethingistrue() do
something()
end
repeat
something()
until somethingistrue()
cases = { key1 = dothis, key2 = dothat, key3 = dotheother }
cases[key]() --equivalent to dothis(), dothat(), or dotheother() respectively</lang>
Make
An if condition using pure make (no gmake extensions) <lang make># make -f do.mk C=mycond if C=0
if:
-@expr $(C) >/dev/null && make -f do.mk true; exit 0 -@expr $(C) >/dev/null || make -f do.mk false; exit 0
true:
@echo "was true."
false:
@echo "was false."</lang>
Using it <lang make>make -f do.mk if C=0 > was false.
make -f do.mk if C=1 > was true.</lang>
With out using recursion but letting make continue with non-failed targets even when some of the targets failed (-k) <lang make>C=0
if: true false
true:
@expr $(C) >/dev/null && exit 0 || exit 1 @echo "was true."
false:
@expr $(C) >/dev/null && exit 1 || exit 0 @echo "was false."</lang>
Invoking it. Note the use of -k which allows make to evaluate subsequent targets even when a previous non-related target failed. <lang make>|make -f do.mk -s -k C=1 was true.
- Error code 1
|make -f do.mk -s -k C=0
- Error code 1
was false.</lang>
Using gmake
<lang make>A= B=
ifeq "$(A)" "1"
B=true
else
B=false
endif
do:
@echo $(A) .. $(B)</lang>
Using it <lang make>|gmake -f if.mk A=1 1 .. true |gmake -f if.mk A=0 0 .. false</lang>
MATLAB
If statements
Example:
<lang MATLAB>if x == 1
disp 'x==1';
elseif x > 1
disp 'x>1';
else
disp 'x<1';
end</lang>
Switch statements
Example:
<lang MATLAB>switch x
case 1
disp 'Hello';
case 2
disp 'World';
otherwise
disp 'Skynet Active';
end</lang>
MAXScript
if
<lang maxscript>if x == 1 then (
print "one"
) else if x == 2 then (
print "two"
) else (
print "Neither one or two"
)</lang>
case
Form one <lang maxscript>case x of (
1: (print "one") 2: (print "two") default: (print "Neither one or two")
)</lang> Form two <lang maxscript>case of (
(x == 1): (print "one") (x == 2): (print "two") default: (print "Neither one or two")
)</lang>
Metafont
<lang metafont>if conditionA:
% do something
elseif conditionB:
% do something
% more elseif, if needed... else:
% do this
fi;</lang>
The particularity of if construct in Metafont is that it can be part of an expression, and the "do something" does not need to fit into the syntactic structure. E.g. we can write something like
<lang metafont>b := if a > 5: 3 + else: 2 - fi c;</lang>
Alone, the code 3 + does not mean anything; but once the condition is evaluated, the whole expression must become "correct"; e.g. if a > 5, the expression will be b := 3 + c;.
There are no other kind of conditional structures, but the great flexibility of Metafont allows for sure to create "new syntaxes" similar to switches or whatever needed.
Modula-2
if-then-else
<lang modula2>IF i = 1 THEN
InOut.WriteString('One')
ELSIF i = 2 THEN
InOut.WriteString('Two')
ELSIF i = 3 THEN
InOut.WriteString('Three')
ELSE
InOut.WriteString('Other')
END;</lang>
Case
<lang modula2>CASE i OF
1 : InOut.WriteString('One')
| 2 : InOut.WriteString('Two') | 3 : InOut.WriteString('Three') ELSE
InOut.WriteString('Other')
END</lang>
Modula-3
if-then-else
<lang modula3>IF Foo = TRUE THEN
Bar();
ELSE
Baz();
END;</lang>
<lang modula3>IF Foo = "foo" THEN
Bar();
ELSIF Foo = "bar" THEN
Baz();
ELSIF Foo = "foobar" THEN
Quux();
ELSE
Zeepf();
END;</lang>
Case
<lang modula3>CASE Foo OF | 1 => IO.Put("One\n"); | 2 => IO.Put("Two\n"); | 3 => IO.Put("Three\n"); ELSE
IO.Put("Something\n");
END;</lang>
Type-case
TYPECASE is used on reference types to perform different operations, depending on what it is a reference to. <lang modula3>TYPECASE ref OF | NULL => IO.Put("Null\n"); | CHAR => IO.Put("Char\n"); | INTEGER => IO.Put("Integer\n"); ELSE
IO.Put("Something\n");
END;</lang>
MUMPS
If / I
<lang MUMPS> IF A GOTO Label</lang>
Some versions of MUMPS do allow an ELSE statement, which can be abbreviated to E. Instead of looking at the previous IF statment, it looks at the value of the system variable $TEST. $TEST is set whenever a conditional statement is executed, thus could be set without the programmer realizing it. For example: <lang MUMPS> IF T DO SUBROUTINE ELSE DO SOMETHING</lang> isn't clear because the function SUBROUTINE might change the value of $TEST.
$Select / $S
<lang MUMPS> WRITE $SELECT(1=2:"Unequal",1=3:"More unequal",1:"Who cares?")</lang>
The $Select statement contains couplets consisting of a conditional test, followed by a colon, and what to return if that condition is true. The couplets are separated by commas. Nonzero numbers evaluate as true. Typically an explicitly true condition is placed in the final couplet. If no conditions are true, an error is returned and the program aborts.
:
<lang MUMPS> SET:(1=1) SKY="Blue"
GOTO:ReallyGo LABEL QUIT:LoopDone WRITE:NotLastInSet ","</lang>
Most commands can take a "postconditional", which is a colon and some conditional statement immediately after the command followed by a space and the usual arguments of the command. The command is executed only if the conditional statement evaluates to true.
The exceptions are FOR, IF, ELSE, and READ. For the Read command, a number (or numeric expression) after a colon is the number of seconds to wait for a user to make an entry before throwing an error.
Nemerle
if-else
if (cond) <then> else <this>; is an expression in Nemerle, producing side effects (<then>|<this>) but not evaluating to anything. when and unless are macros for which <this> = null. cond must be an expression that evaluates to a bool (true|false), other types aren't automatically assigned truth or falsehood as in some languages. <lang Nemerle>if (the_answer == 42) FindQuestion() else Foo(); when (stock.price < buy_order) stock.Buy(); unless (text < "") Write(text);</lang>
match
Much cleaner than stacked if-else's, similar in some ways to switch-case (but more flexible). See here, here, or, for extra detail, the reference. <lang Nemerle>match(x) {
|1 => "x is one" |x when (x < 5) => "x is less than five" |_ => "x is at least five"
}</lang>
newLISP
if
Interpreter: newLISP v.9.0 <lang lisp>(set 'x 1) (if (= x 1) (println "is 1"))</lang> A third expression can be used as an else. <lang lisp>(set 'x 0) (if (= x 1) (println "is 1") (println "not 1"))</lang>
Object Pascal
- See Pascal
Objective-C
- See also C
One difference: the preprocessor has been extended with an #import directive which does the same thing as #include with "include guards".
Objeck
if-else
<lang objeck> a := GetValue(); if(a < 5) {
"less than 5"->PrintLine();
} else if(a > 5) {
"greater than 5"->PrintLine();
} else {
"equal to 5"->PrintLine();
}; </lang>
select
<lang objeck> a := GetValue(); select(a) {
label 5: {
"equal to 5"->PrintLine();
}
label 7: {
"equal to 7"->PrintLine();
}
other: {
"another value"->PrintLine();
}
}; </lang>
OCaml
if-then-else
<lang ocaml>let condition = true
if condition then
1 (* evaluate something *)
else
2 (* evaluate something *)</lang>
If-then-else has higher precedence than ; (the semicolon), so if you want to have multiple statements with side effects inside an "if", you have to enclose it with begin...end or with parentheses:
<lang ocaml>if condition then begin
(); (* evaluate things for side effects *) 5
end else begin
(); (* evaluate things for side effects *) 42
end</lang>
match-with
<lang ocaml>match expression with | 0 -> () (* evaluate something *) | 1 -> () (* evaluate something *) | n when n mod 2 = 0 -> () (* evaluate something *) | _ -> () (* evaluate something *)</lang>
The first | is optional, and usually omitted.
Match is especially useful for Pattern Matching on various types of data structures.
Nested match's need to be surrounded by begin-end or parentheses, or else it won't know where it ends.
Octave
if-then-elseif-else <lang octave>if (condition)
% body
endif
if (condition)
% body
else
% otherwise body
endif
if (condition1)
% body
elseif (condition2)
% body 2
else
% otherwise body
endif</lang>
switch <lang octave>switch( expression )
case label1 % code for label1 case label2 % code for label2 otherwise % none of the previous
endswitch</lang>
Labels can be numeric or string, or cells to group several possibilities:
<lang octave>switch ( x )
case 1
disp("it is 1");
case { 5,6,7 }
disp("it is 5, or 6 or 7");
otherwise
disp("unknown!");
endswitch</lang>
Oz
if-then-else
<lang oz>proc {PrintParity X}
if {IsEven X} then
{Show even}
elseif {IsOdd X} then
{Show odd}
else
{Show 'should not happen'}
end
end</lang>
if-then-else as a ternary operator
<lang oz>fun {Max X Y}
if X > Y then X else Y end
end</lang>
case statement
<lang oz>fun {Fac X}
case X of 0 then 1
[] _ then X * {Fac X-1}
end
end</lang>
PARI/GP
GP uses a simple if statement:
<lang parigp>if(condition, do_if_true, do_if_false)</lang>
and short-circuit && and || (which can be abbreviated & and | if desired).
PARI can use all of the usual C conditionals.
Pascal
if-then-else
<lang pascal>IF condition1 THEN
procedure1
ELSE
procedure3;
IF condition1 THEN
BEGIN procedure1; procedure2; END
ELSE
procedure3;
IF condition 1 THEN
BEGIN procedure1; procedure2; END
ELSE
BEGIN procedure3; procedure4; END;</lang>
case
Case selectors must be an ordinal type. This might seem to be a restriction, but with a little thought just about anything can be resolved to an ordinal type. Additionally, each selector may consist of more then one item. The optional ELSE keyword provides a default for values that do not match any of the given cases.
In Pascal there is no fall-through to the next case. When execution reaches the end of a matching clause, it continues after the end of the case statement, not in the code for the next case.
<lang pascal>case i of
1,4,9: { executed if i is 1, 4 or 9 }
DoSomething;
11, 13 .. 17: { executed if i is 11, 13, 14, 15, 16 or 17 }
DoSomethingElse;
42: { executed only if i is 42 }
DoSomeOtherThing;
else
DoYetAnotherThing;
end;</lang>
Given the variable "X" as a char the following is valid:
<lang pascal>Case X of
'A' : statement ; 'B' : statement ; in ['C'..'W'] : statement ;
else
Statement ;
end;</lang>
Perl
if/else
if ($expression) {
do_something;
};
# postfix conditional do_something if $expression;
if ($expression) {
do_something;
} else {
do_fallback;
};
if ($expression1) {
do_something;
} elsif ($expression2) {
do_something_different;
} else {
do_fallback;
};
unless
unless behaves like if, only logically negated. You can use it wherever you can use if. An unless block can have elsif and else blocks, but there is no elsunless.
ternary operator
This is the same as the if/else example, only less readable. But it returns the value of its executed branch.
$expression ? do_something : do_fallback;
logical operators
$condition and do_something is equivalent to $condition ? do_something : $condition.
$condition or do_something is equivalent to $condition ? $condition : do_something.
&& and || have the same semantics as and and or, respectively, but their precedence is much higher, making them better for conditional expressions than control flow.
switch
<lang perl>use feature "switch"; given ($input) {
when (0) { print 'input == 0'; }
when ('coffee') { print 'input equal coffee'; }
when ([1..9]) { print 'input between 1 and 9'; }
when (/rats/) { print 'input matches rats'; }
default { do_fallback; }
}</lang>
Perl 6
if, else, elsif, unless, and given work much as they do in Perl 5, with the following differences:
- All the parentheses are now optional.
-
unlessno longer permitselsiforelseblocks. - If the block of an
if,elsif, orunlesshas a nonzero arity, the value of the conditional expression is used as an argument to the block: <lang perl6>if won() -> $prize { say "You won $prize."; }</lang> If anelseblock has a nonzero arity, it recieves the value of the condition tested by the lastiforelsif.
when blocks are now allowed "in any block that sets $_, including a
for loop (assuming one of its loop variables is bound to $_)
or the body of a method (if you have declared the invocant as $_)." See Synopsis 4.
The ternary operator now looks like this:
<lang perl6>$expression ?? do_something !! do_fallback</lang>
and, or, &&, and || work as in Perl 5.
PHP
if
Interpreter: PHP 3.x, 4.x, 5.x
<lang php><?php
$foo = 3;
if ($foo == 2)
//do something
if ($foo == 3)
//do something
else
//do something else
if ($foo != 0) {
//do something
} else {
//do another thing
}
?></lang>
switch
Interpreter: PHP 3.x & 4.x & 5.x
<lang php><?php
switch ($i) {
case "apple":
echo "i is apple";
break;
case "bar":
echo "i is bar";
break;
case "cake":
echo "i is cake";
break;
}
?></lang>
See Also
PicoLisp
Two-way conditions
<lang PicoLisp>(if (condition) # If the condition evaluates to non-NIL
(then-do-this) # Then execute the following expression (else-do-that) # Else execute all other expressions (and-more) )
(ifn (condition) # If the condition evaluates to NIL
(then-do-this) # Then execute the following expression (else-do-that) # Else execute all other expressions (and-more) )</lang>
One-way conditions <lang PicoLisp>(when (condition) # If the condition evaluates to non-NIL
(then-do-this) # Then execute tall following expressions (and-more) )
(unless (condition) # If the condition evaluates to NIL
(then-do-this) # Then execute all following expressions (and-more) )</lang>
Four-way condition
<lang PicoLisp>(if2 (condition1) (condition2) # If both conditions evaluate to non-NIL
(expression-both) # Then execute this expression (expression-first) # Otherwise this for the first (expression-second) # or this the second condition. (expression-none) # If both are NIL, all following expressions (and-more) )</lang>
Multiple conditions
<lang PicoLisp>(cond
((condition1) # If this condition evaluates to non-NIL
(expression 1) # Execute these expression(s)
(more 1) )
((condition2) # Otherwise, if this evaluates to non-NIL
(expression 2) # Execute these expression(s)
(more 2) )
(T # If none evaluated to non-NIL
(expression 1) # Execute these expression(s)
(more 1) )
(nond
((condition1) # If this condition evaluates to NIL
(expression 1) # Execute these expression(s)
(more 1) )
((condition2) # Otherwise, if this evaluates to NIL
(expression 2) # Execute these expression(s)
(more 2) )
(NIL # If none evaluated to NIL
(expression 1) # Execute these expression(s)
(more 1) )</lang>
Selection
<lang PicoLisp>(case (expression) # Evaluate the expression
(value1 # If it is equal to, or member of, 'value1'
(do-this1) # Execute these expression(s)
(do-that1) )
(value2 # Else if it is equal to, or member of, 'value2
(do-this2) # Execute these expression(s)
(do-that2) )
(T # Else execute final expression(s)
(do-something-else) ) )</lang>
PL/I
if-then-else
<lang pli>if condition then
statement;
else
statement;
if condition then
do; statement-1; . . statement-n; end;
else
statement;</lang>
case
The PL/I 'case' statement has two possible formats:
select - format 1
<lang pli>select (i); /* select on value of variable */
when (1,4,9)
do;
statement(s)
end;
when (11, 42)
do;
statement(s)
end;
other /* everything else */
do;
statement(s)
end;
end;</lang>
select - format 2
<lang pli>select; /* select first matching condition */
when (i = 4);
do;
statement(s)
end;
when (this = that)
do;
statement(s)
end;
when (string = 'ABCDE')
do;
statement(s)
end;
other
do;
statement(s)
end;
end;</lang>
Notes:
- in PL/I there is no fall-through to the next when. When execution reaches the end of a matching clause, it continues after the end of the select statement, not in the code for the next case.
- the do ... end statements can be omitted if the when clause is followed by a single statement.
- if no other (or in full: otherwise) statement is present and non of the when cases is matched, the program will end in error.
Pop11
The simplest conditional is:
<lang pop11>if condition then
;;; Action
endif;</lang>
Two way conditional looks like:
<lang pop11>if condition then
;;; Action1
else
;;; Alternative action
endif;</lang>
One can do multiway choice using elseif clause
<lang pop11>if condition1 then
;;; Action1
elseif condition2 then
;;; Action1
elseif condition2 then
;;; Action2
elseif condition3 then
;;; Action3
else
;;; Alternative action
endif;</lang>
Instead of if keyword one can use unless keyword.
<lang pop11>unless condition then /* Action */ endunless;</lang>
has the same meaning as
<lang pop11>if not(condition) then /* Action */ endif;</lang>
One can also use elseunless keword.
<lang pop11>if condition1 then
;;; Action1
elseunless condition2 then
;;; Action2
endif;
;;; Action2
endif;</lang>
has the same meaning as
<lang pop11>if condition1 then
;;; Action1
elseif not(condition2) then
;;; Action2
endif;</lang>
Note that conditional must end in matching keyword, if must be finished by endif, unless must be finished by endunless (in the middle one can mix elseif with elseunless.
Pop11 conditional is an expression:
<lang pop11>if x > 0 then 1 elseif x < 0 then -1 else 0 endif -> sign_x ;</lang>
assigns sign of x to sign_x.
Instead of multiway if one can use switchon construct (which is equivalent to a special case of if, but may be shorter).
<lang pop11>switchon(x)
case .isstring then printf('A1');
notcase .isinteger then printf('A2');
case = 2 orcase = 3 then printf('A3');
case > 4 andcase < 15 then printf('A4');
else printf('A5');
endswitchon;</lang>
There is also multiway goto statement and conditional control transfers, we explain them together with other control transfers and loops (in case of loop exit/continue statements).
Pop11 also has preprocessor allowing conditional compilation:
<lang pop11>#_IF condition1 /* Variant 1 */
- _ELSEIF condition2
/* Variant 2 */
- _ELSE
/* Variant 3 */
- _ENDIF</lang>
condition1 and condition2 are arbitrary Pop11 expressions (they have access to all previously compiled code).
Also note that Pop11 syntax is user extensible, so users may create their own conditional constructs.
PostScript
The "if" operator uses two items form the stack, a procedure and a boolean. It will execute the procedure if the boolean is true. It will not leave anything on the stack (but the procedure might):
<lang postscript>9 10 lt {(9 is less than 10) show} if</lang>
The "ifelse" operator expects two procedures and executes the one or the other depending on the value of the boolean. I.e. this:
<lang postscript>/a 5 lt {(yeah)} {(nope)} ifelse show</lang>
will render either the string "yeah" or "nope" depending on whether a is less than 5 or not.
PowerShell
If, ElseIf, Else
<lang powershell># standard if if (condition) {
# ...
}
- if-then-else
if (condition) {
# ...
} else {
# ...
}
- if-then-elseif-else
if (condition) {
# ...
} elseif (condition2) {
# ...
} else {
# ...
}</lang>
Switch
<lang powershell># standard switch switch ($var) {
1 { "Value was 1" }
2 { "Value was 2" }
default { "Value was something else" }
}
- switch with wildcard matching
switch -Wildcard ($var) {
"a*" { "Started with a" }
"*x" { "Ended with x" }
}
- switch with regular expression matching
switch -Regex ($var) {
"[aeiou]" { "Contained a consonant" }
"(.)\1" { "Contained a character twice in a row" }
}
- switch allows for scriptblocks too
switch ($var) {
{ $_ % 2 -eq 0 } { "Number was even" }
{ $_ -gt 100 } { "Number was greater than 100" }
}
- switch allows for handling a file
switch -Regex -File somefile.txt {
"\d+" { "Line started with a number" }
"\s+" { "Line started with whitespace" }
}</lang>
PureBasic
If, Elseif, Else
<lang PureBasic>If a = 0
Debug "a = 0"
ElseIf a > 0
Debug "a > 0"
Else
Debug "a < 0"
EndIf</lang>
Select
<lang PureBasic>Variable = 2
Select Variable
Case 0 Debug "Variable = 0"
Case 10, 11, 99 Debug "Variable is 10, 11 or 99"
Case 20 To 30 Debug "Variable >= 20 And Variable <= 30"
Default Debug "Variable = something else..."
EndSelect</lang>
CompilerIf
Compiler conditional structures works like normal conditional structures, except they are evaluated at compile time, and thus have to use constant expressions. Any defined constant can be used, these examples uses built-in constants. <lang PureBasic> CompilerIf #PB_Compiler_OS = #PB_OS_Linux And #PB_Compiler_Processor = #PB_Processor_x86
Debug "Compiled on x86 Linux"
CompilerElse
Debug "Compiled on something else"
CompilerEndIf </lang>
CompilerSelect
<lang PureBasic> CompilerSelect #PB_Compiler_OS
CompilerCase #PB_OS_Linux Debug "Compiled on Linux" CompilerCase #PB_OS_Windows Debug "Compiled on Windows" CompilerCase #PB_OS_MacOS Debug "Compiled on Mac OS" CompilerDefault Debug "Compiled on something else"
CompilerEndIf </lang>
Python
if-then-else
if x == 0:
foo()
elif x == 1:
bar()
elif x == 2:
baz()
else:
boz()
ternary expressions
Interpreter: Python 2.5
true_value if condition else false_value
Example: <lang python>secret='foo'
print 'got it' if secret=='foo' else 'try again'
'got it'</lang>
Note: this syntax is valid as an expression, the clauses cannot constain statements. The foregoing example is equivalent to:
<lang python>secret = 'foo'
result = 'got it' if secret=='foo' else 'try again' print result
'got it'</lang>
Function dispatch dictionary
In some cases it's useful to associate functions with keys in a dictionary; and simply use this in lieu of long sequences of "if...elif...elif..." statements.
dispatcher = dict()
dispatcher[0]=foo # Not foo(): we bind the dictionary entry to the function's object,
# NOT to the results returned by an invocation of the function
dispatcher[1]=bar
dispatcher[2]=baz # foo,bar, baz, and boz are defined functions.
# Then later
results = dispatcher.get(x, boz)() # binding results to a name is optional
# or with no "default" case:
if x in dispatcher:
results=dispatcher[x]()
This can be particularly handy when using currying techniques, or when lambda expressions or meta-function generators (factories) can be used in place of normal named functions.
In general a dispatch table or class/object abstraction (using dynamic method over-rides) is considered preferable to chains of if ... elif ... elif ... in Python programming.
R
if-else
<lang R>#Single line example
#x is assumed to be scalar
if(x < 3) message("x is less than 3") else if(x < 5) message("x is greater than or equal to 3 but less than 5") else message("x is greater than or equal to 5")
- Block example
if(x < 3)
{
x <- 3
warning("x has been increased to 3")
} else
{
y <- x^2
}
- It is important that the else keyword appears on the same line as the closing '}' of the if block.</lang>
ifelse
<lang r>#ifelse is a vectorised version of the if/else flow controllers, similar to the C-style ternary operator.
x <- sample(1:10, 10) ifelse(x > 5, x^2, 0)</lang>
switch
<lang r>#Character input
calories <- function(food) switch(food, apple=47, pizza=1500, stop("food not known"))
calories("apple") #47
calories("banana") #throws an error
- Numeric input
alphabet <- function(number) switch(number, "a", "ab", "abc") alphabet(3) # "abc" alphabet(4) # NULL
- Note that no 'otherwise' option is allowed when the input is numeric.</lang>
Retro
if, ifTrue, and ifFalse
<lang Retro>( condition ) [ ( true statements ) ] ifTrue ( condition ) [ ( false statements ) ] ifFalse ( condition ) [ ( true statements ) ] [ ( false statements ) ] if</lang>
These forms can be used interactively, or inside function definitions.
when
<lang Retro>: foo ( n- )
[ 1 = ] [ drop ( if quote evaluates to true ) ] when [ 2 = ] [ drop ( if quote evaluates to true ) ] when [ 3 = ] [ drop ( if quote evaluates to true ) ] when drop ( default action ) ;</lang>
REXX
IF THEN --- IF THEN/ELSE
<lang rexx> if y then x=6 /* Y must be either 0 or 1 */
if t**2>u then x=y
else x=-y
if t**2>u then do j=1 to 10; say prime(j); end
else x=-y
if z>w+4 then do
z=abs(z)
say 'z='z
end
else do; z=0; say 'failed.'; end
if x>y & c*d<sqrt(pz) |,
substr(abc,4,1)=='@' then if z=0 then call punt
else nop
else if z<0 then z=-y
</lang>
SELECT WHEN
<lang rexx>
/*the WHEN conditional operators are the same as */
/*the IF conditional operators. */
select
when t<0 then z=abs(u)
when t=0 & y=0 then z=0
when t>0 then do
y=sqrt(z)
z=u**2
end
/*if control reaches this point and none of the WHENs */
/*were satisfiied, a SYNTAX condition is raised (error).*/
end
</lang>
SELECT WHEN/OTHERWISE
<lang rexx>
select
when a=='angel' then many='host'
when a=='ass' | a=='donkey' then many='pace'
when a=='crocodile' then many='bask'
when a=='crow' then many='murder'
when a=='lark' then many='ascension'
when a=='quail' then many='bevy'
when a=='wolf' then many='pack'
otherwise say
say '*** error! ***'
say a "isn't one of the known thingys."
say
exit 13
end
</lang>
Rhope
if-then-else
<lang rhope>If[cond] |:
Do Something[]
- ||:
Do Something Else[]
- |</lang>
RLaB
if
Block of instructions following the if command has to be always enclosed in curly brackets. <lang RLaB> if (x==1) {
// do something
} </lang>
if-else
If there are branching within the command, respective blocks have to be enclosed in the blocks preceding it. Consider an example:
<lang RLaB> if (x==1) {
// do something if x is 1 y = const.pi;
else
// do something if x is not 1 y = sin(const.pi*(1-x)) / (1-x);
} </lang>
<lang RLaB> if (x==1) {
// do something if x is 1 y = const.pi;
else if (x == 2) {
// do something if x is 2 y = sin(const.pi*(1-x)) / (1-x);
else
// do something in all the other cases y = rand();
}} </lang>
Ruby
See Conditional Structures/Ruby
Sather
<lang sather> if EXPR then
-- CODE
elsif EXPR then
-- CODE
else
-- CODE
end;</lang>
EXPR must evaluate to BOOL (true or false); elsif and else are optional.
<lang sather> case EXPR
when EXPRL then
-- CODE
when EXPRL then
-- CODE
else
-- CODE
end;</lang>
EXPRL is a single expression or a comma-separated list of exressions. The expressions must evaluate to comparable objects (the method is_eq must be implemented)
Scheme
Procedures can be categorised as primitive or derived. Derived procedures can be defined in terms of primitive procedures.
Primitive
if
<lang>(if <test> <consequent> <alternate>)</lang> <lang>(if <test> <consequent>)</lang> Example: <lang scheme>(display
(if (> 1 2)
"yes"
"no"))
(newline) (display
(if (> 1 2)
(- 1 2)))
(newline)</lang> Output: <lang>no
- <unspecified></lang>
Derived
cond
<lang>(cond <clause1> <clause2> ...)</lang> Example: <lang scheme>(display
(cond ((> 1 2) "greater")
((< 1 2) "less")))
(newline) (display
(cond ((> 1 1) "greater")
((< 1 1) "less")
(else "equal")))
(newline)</lang> Output: <lang>less equal</lang>
case
<lang>(case <key> <clause1> <clause2> ...)</lang> Example: <lang scheme>(display
(case (* 2 3) ((2 3 5 7) "prime") ((1 4 6 8 9) "composite")))
(newline) (display
(case (car (list c d)) ((a e i o u) "vowel") ((w y) "semivowel") (else "consonant")))
(newline)</lang> Output: <lang>composite consonant</lang>
Seed7
if-then-else
There can be single or multiple statements. An if-statement can have multiple elsif parts. <lang seed7>if condition then
statement
end if;
if condition then
statement1
else
statement2;
end if;
if condition1 then
statement1
elsif condition2 then
statement2;
end if;
if condition1 then
statement1
elsif condition2 then
statement2;
else
statement3;
end if;</lang>
case
<lang seed7>case i of
when {1, 4, 9}: # Executed if i is 1, 4 or 9
statement1;
when {11} | {13 .. 17}: # Executed if i is 11, 13, 14, 15, 16 or 17
statement2;
when {42}: # Executed only if i is 42
statement3;
otherwise:
statement4;
end case;</lang>
SIMPOL
if-else if-else
<lang simpol>if x == 1
foo()
else if x == 2
bar()
else
foobar()
end if</lang>
ternary if function
<lang simpol>.if(x == 1, "hello", "world")</lang>
Slate
ifTrue/ifFalse
<lang slate>"Conditionals in Slate are really messages sent to Boolean objects. Like Smalltalk. (But the compiler might optimize some cases)"
balance > 0
ifTrue: [inform: 'still sitting pretty!'.]
ifFalse: [inform: 'No money till payday!'.].</lang>
caseOf:otherwise:
<lang slate>c@(Net URLPathEncoder traits) convert [ | byte1 byte2 byte3 digit1 digit2|
[c in isAtEnd] whileFalse:
[byte1: c in next.
byte1 caseOf: {
$+ -> [c out nextPut: $\s].
$% -> [byte2: c in next.
byte3: c in next.
digit1: (byte2 toDigit: 16).
digit2: (byte3 toDigit: 16).
digit1 isNil \/ [digit2 isNil] ifTrue: [error: 'Error reading hex sequence after %'].
c out nextPut: (digit1 * 16 + digit2 as: c out elementType)].
} otherwise: [c out nextPut: byte1].
].
].</lang>
whileTrue:/whileFalse:
<lang slate>[p isAtEnd] whileFalse: [p next evaluate]].</lang>
Smalltalk
The pattern for handling a multi-option switch is to create classes for the various options, and let Polymorphism take care of the decisions.
ifTrue/ifFalse
<lang smalltalk>"Conditionals in Smalltalk are really messages sent to Boolean objects"
balance > 0
ifTrue: [Transcript cr; show: 'still sitting pretty!'.]
ifFalse: [Transcript cr; show: 'No money till payday!'.].</lang>
You can also use them as the ternary operator
<lang smalltalk>abs := x > 0 ifTrue: [ x ] ifFalse: [ x negated ]</lang>
SNOBOL4
SNOBOL4 has no structured programming features, but the two constructs in question could be easily emulated with FAILURE/SUCCESS and indirect jumps
<lang snobol> A = "true"
- "if-then-else"
if A "true" :s(goTrue)f(goFalse) goTrue output = "A is TRUE" :(fi) goFalse output = "A is not TRUE" :(fi) fi
- "switch"
switch A ("true" | "false") . switch :s($("case" switch))f(default) casetrue output = "A is TRUE" :(esac) casefalse output = "A is FALSE" :(esac) default output = "A is neither FALSE nor TRUE" esac end</lang>
SNUSP
<lang snusp>$==?\==zero=====!/==#
\==non zero==/</lang>
? is the only conditional operator. It skips one character if the current cell is zero.
! is an unconditional skip. !/ is the idiom for joining two lines of execution. ?! inverts the test.
\ and / redirect the flow of control. All the other characters besides $ and # are commentary.
SQL
Conditional Expression
<lang sql>case when a then b else c end
declare @n int set @n=124 print case when @n=123 then 'equal' else 'not equal' end
--If/ElseIf expression set @n=5 print case when @n=3 then 'Three' when @n=4 then 'Four' else 'Other' end</lang>
If/Else
<lang sql>declare @n int set @n=123 if @n=123
BEGIN --begin/end needed if more than one statement inside print 'one two three' END
ELSE
if @n=124 print 'one two four' else print 'other'</lang>
Tcl
if-then-else
<lang tcl>if {$foo == 3} {
puts "foo is three"
} elseif {$foo == 4} {
puts "foo is four"
} else {
puts "foo is neither three nor four"
}</lang> or (using the ternary operator of expressions) <lang tcl>set result [expr { $foo == 3 ? "three" : "not three" }]</lang>
switch
<lang tcl>switch -- $foo {
3 {puts "foo is three"}
4 {puts "foo is four"}
default {puts "foo is something else"}
}</lang> Note that the switch command can also use glob matching (like case in the Bourne Shell) or regular-expression matching.
Toka
ifTrue
( condition ) ( quote ) ifTrue
<lang toka>100 100 = [ ." True\n" ] ifTrue 100 200 = [ ." True\n" ] ifTrue</lang>
ifFalse
( condition ) ( quote ) ifFalse
<lang toka>100 100 = [ ." True\n" ] ifFalse 100 200 = [ ." True\n" ] ifFalse</lang>
ifTrueFalse
( condition ) ( true quote ) ( false quote ) ifTrueFalse
<lang toka>100 100 = [ ." Equal\n" ] [ ." Not Equal\n" ] ifTrueFalse 100 200 = [ ." Equal\n" ] [ ." Not Equal\n" ] ifTrueFalse</lang>
TorqueScript
if-then-else
<lang tqs>// numbers and objects if(%num == 1) { foo(); } else if(%obj == MyObject.getID()) { bar(); } else { deusEx(); }
// strings if(%str $= "Hello World") { foo(); } else if(%str $= "Bye World") { bar(); } else { deusEx(); }</lang>
switch
<lang tqs>// numbers and objects switch(%num) { case 1: one(); case 2: twoThreeOrFour(); case 3: twoThreeOrFour(); case 4: twoThreeOrFour(); case 5: five(); case MyObject.getID(): anObject(); default: everythingElse(); }
// strings switch$(%str) { case "Hello": arrival(); case "Goodbye": departure(); default: somethingElse(); }</lang>
conditional (ternary) operator (?:)
<lang tqs>%formatted = %str @ ((getSubStr(%str,strLen(%str) - 1,1) $= "s") ? "'" : "'s");</lang>
Trith
branch
<lang trith>true ["yes" print] ["no" print] branch</lang>
when
<lang trith>true ["yes" print] when</lang>
unless
<lang trith>false ["no" print] unless</lang>
TUSCRIPT
IF ELSEIF ELSE ENDIF
<lang tuscript> $$ MODE TUSCRIPT
condition="c" IF (condition=="a") THEN
---> do something
ELSEIF (condition=="b") THEN
---> do something
ELSE
---> do something
ENDIF </lang>
SELECT CASE DEFAULT ENDSELECT
<lang tuscript> $$ MODE TUSCRIPT
days="Monday'Tuesday'Wednesday'Thursday'Friday'Saturday'Sunday" dayofweek=DATE (today,day,month,year,number) day=SELECT (days,#dayofweek)
SELECT day CASE "Monday"
---> do something
CASE "Saturday","Sunday"
---> do something
DEFAULT
---> do something
ENDSELECT </lang>
UNIX Shell
If conditionals
The basic syntax is if command-list; then command-list; fi. If the first command list succeeds (by returning 0 for success), then the shell runs the second command list.
<lang sh>if test 3 -lt 5; then echo '3 is less than 5'; fi</lang>
Else and elif
There are optional elif (else if) and else clauses.
<lang sh>if test 4 -ge 6; then echo '4 is greater than or equal to 6' elif test 4 -lt 6; then echo '4 is less than 6' else echo '4 compares not to 6' fi</lang>
Switch conditionals
The Unix shell provides support for multibranch switch conditional constructs using the case statement:
<lang sh>case value in
choicea) foo ;; choiceb) bar ;;
esac</lang>
Conditional branching using operators
One can also use && and || as conditional structures; see short-circuit evaluation#UNIX Shell.
<lang sh>test 3 -lt 5 && echo '3 is less than 5' test 4 -ge 6 || echo '4 is not greater than or equal to 6'</lang>
Conditional loops
The Unix shell also supports conditional loops:
<lang sh># This is a while loop l=1 while [ l -le 5 ]; do
echo $l
done
- This is an until loop
l=1 until [ l -eq 5 ]; do
echo $l
done</lang>
C Shell
The single-line if syntax is if (expression) simple-command.
<lang csh>if (3 < 5) echo '3 is less than 5' if ({ grep -q ^root: /etc/passwd }) echo 'passwd has root'</lang>
The multi-line if syntax has a then clause, and can have optional else if and else clauses. Each clause may contain multiple commands.
<lang csh>if (4 >= 6) then echo '4 is greater than or equal to 6' else if (4 < 6) then echo '4 is less than 6' else echo '4 compares not to 6' endif</lang>
V
ifThenElse
<lang v>[true]
['is true' puts] ['is false' puts]
ifte
=is true</lang>
ifThen
<lang v>[true]
['is true' puts]
if =is true</lang>
When
<lang v>3 [
[1 =] [1 *] [2 =] [10 *] [3 =] [100 *] [4 =] [1000 *]
] when
=300</lang>
Choice
<lang v>true
1 2
choice
=1
false
1 2
choice
=2</lang>
VBScript
if-then-else
<lang vbscript>if (condition) then
result = "met"
else
Result = "not met"
end if</lang>
Visual Basic .NET
if-then-else
Basic <lang vbnet>Dim result As String, a As String = "pants", b As String = "glasses"
If a = b Then
result = "passed"
Else
result = "failed"
End If</lang>
Condensed <lang vbnet>Dim result As String, a As String = "pants", b As String = "glasses"
If a = b Then result = "passed" Else result = "failed"
If a = b Then
result = "passed"
Else : result = "failed" End If
If a = b Then : result = "passed" Else
result = "failed"
End If</lang>
if-then-elseif
<lang vbnet>Dim result As String, a As String = "pants", b As String = "glasses"
If a = b Then
result = "passed"
ElseIf a <> b Then
result = "failed"
Else
result = "impossible"
End If</lang>
select-case-else
<lang vbnet>Dim result As String, a As String = "pants", b As String = "glasses"
Select Case a
Case b result = "match" Case a : result = "duh" Case Else result = "impossible"
End Select</lang>
inline-conditional
<lang vbnet>Imports Microsoft.VisualBasic
...
Dim result As String = CType(IIf("pants" = "glasses", "passed", "failed"), String) 'VB 1-8
Dim result As String = If("pants" = "glasses", "passed", "failed") 'VB 9</lang>
generic-inline-conditional
<lang vbnet>Imports Microsoft.VisualBasic
...
Function IIf2(Of T)(ByVal condition As Boolean, ByVal truepart As T, ByVal falsepart As T) As T
If condition Then Return truepart Else Return falsepart
End Function
...
Dim result As String = IIf2("pants" = "glasses", "passed", "failed") ' type is inferred</lang>
generic-inline-conditional
Language Version: 9.0+
<lang vbnet>Dim result As String = If("pants" = "glasses", "passed", "failed") ' type is inferred</lang>
Vorpal
if-then-else
<lang vorpal>if(condition){
result = 'met'
} else{
result = 'not met'
}</lang>
Wrapl
simple conditional
Conditionals in Wrapl are expressions. Either success or failure can be omitted from the expression. <lang wrapl>condition => success // failure condition => success condition // failure</lang>
goal directed evaluation
Wrapl's goal directed evaluation can be used to control conditional execution. The select-right operator & produces the values of the right operand for each value produced by the left operand. Thus if the left operand fails to produce any values, the right operand is never evaluated. <lang wrapl>condition & success</lang> The sequence operator | produces the values of the left operand followed by the values of the right operand. Thus if the left operand produces enough values (for example in a context where only one value is required), the right operand is never evaluated. <lang wrapl>condition | failure</lang>
X86 Assembly
ifs/elseifs/elses
Assembly doesn't work on if/else if/else statements(Unless you're using MASM or alike assemblers:)). Rather, it has conditional jumps which work off flags set by the comparison. Take this general statement from C. <lang c> if(i>1)
DoSomething
FailedSoContinueCodeExecution. </lang> There are actually a number of ways to implement that in assembly. The most typical way would be something like.. <lang asm> cmp i, 1 jg _DoSomething FailedSoContinueCodeExecution </lang> Using the "jg" instruction,our code will jump to _DoSomething if the comparison(cmp i,1) made our ZF(ZeroFlag) flag well, zero. Which means only 1 thing. It is in fact greater than. In contrast, if i is in fact equal or less than 1, ZF is set to 1. The Zero Flag will remain set as long as we don't use any instructions that alter flags(comparisons for example). So, here's another C example <lang c> if(i>1)
DoSomething
else if(i<=1)
DoSomethingElse
FailedSoContinueCodeExecution
</lang>
In this case, we can use our previous example as a skeleton.
<lang asm>
cmp i, 1
jg _DoSomething
jle _DoSomethingElse
FailedSoContinueCodeExecution
</lang>
This does another state check on the Zero flag(actually jg/jle also check another flag, but that's not overly important) using jle. JumpifLessthanorEqual. Essentially, jle jumps if ZG is set to 1. So, it's jump condition is the opposite to jg.
One last commonly used condition.
<lang c>
if(i==1)
DoSomething
else
DoSomethingElse
FailedSoContinueExecution </lang>
In this case, we'd do this.
<lang asm>
cmp i, 1
je _DoSomething
jne _DoSomethingElse
FailedSoContinueExecution
</lang>
The je/jne jump instructions are again like jg/jle opposites of each other and again like je/jne rely on how the zero flag is set in the previous comparison.
There are many different conditional jumps in assembly and many ways to set them, test, and, or to name a few. The ones covered are just some commonly used ones in order to show how assembly deals with conditional statements.
XSLT
The <xsl:if> element allows simple conditional processing. <lang xml><xsl:if test="condition"> </xsl:if></lang> The <xsl:choose>, <xsl:when>, and <xsl:otherwise> elements allow more general conditional processing. <lang xml><xsl:choose>
<xsl:when test="condition1"> </xsl:when> <xsl:when test="condition2"> </xsl:when> <-- etc. --> <xsl:otherwise> </xsl:otherwise>
</xsl:choose></lang> The XPath expressions allowed for the "test" attribute are those which return a boolean value: <lang xml>@attrib = 'false' position() != last() not( false() ) boolean( $param )</lang>
contains( node, "stuff" ) and (position() > first())
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