Conditional structures
From Rosetta Code
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:
- Conditional structures
- Exceptions
- Flow-control structures
- Loops
Here, we document the conditional structures offered by different programming languages. Common conditional structures are if-then-else and switch.
[edit] 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:
LDA #10
CMP #11
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.
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.
In the following example, the branch will be taken if memory location Variable holds 200:
LDA #200
CMP Variable
BEQ #3 ;if equal, skip ahead 3 bytes...
CLC ;if unequal, continue executing instructions
ADC #1
STA OtherVariable ; ...to here.
Because you don't have to perform a comparison to set the flags, you can perform very fast checks in interative loops:
LDX #100
Loop: ...do something
DEX
BNE Loop
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.
[edit] ActionScript
- See JavaScript
[edit] Aikido
[edit] Conditional Expressions
var x = loggedin ? sessionid : -1
[edit] if..elif..else
if (value > 40) {
println ("OK")
} elif (value < 20) {
println ("FAILED")
} else {
println ("RETRY")
}
[edit] switch
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")
}
[edit] Ada
[edit] if-then-else
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;
[edit] case
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;
[edit] select
Select provides conditional acceptance of entry calls. Select can also be used to conditionally call an entry
[edit] Conditional Accept
select
accept first_entry;
-- do something
or accept second_entry;
-- do something
or terminate;
end select;
[edit] 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.
select
My_Task.Start;
or
delay Timeout_Period;
end select;
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.
[edit] ALGOL 68
See Conditional Structures/ALGOL 68
[edit] AmigaE
IF-THEN-ELSE
IF condition
-> if condition is true...
ELSEIF condition2
-> else if condition2 is true...
ELSE
-> if all other conditions are not true...
ENDIF
or on one single line:
IF condition THEN statement
Ternary IF THEN ELSE
The IF-THEN-ELSE can be used like ternary operator (?: in C)
DEF c
c := IF condition THEN 78 ELSE 19
SELECT-CASE
SELECT var
CASE n1
-> code
CASE n2
-> code
DEFAULT
-> no one of the previous case...
ENDSELECT
Another version allows for ranges:
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
The biggest among n1, n2 and so on, must be not bigger than max_possible_value.
[edit] AppleScript
[edit] if-then-else
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
[edit] AutoHotkey
if, else if, else
ternary if
while (looping if)
; 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
}
[edit] AWK
Conditionals in awk are modelled after C:
if(i<0) i=0; else i=42
including the ternary conditional
i=(i<0? 0: 42)
[edit] BASIC
[edit] if-then-else
Works with: QuickBasic version 4.5 Works with: FreeBASIC version 0.20.0 Single line IF does not require END IF
IF x = 0 THEN doSomething
IF x < 0 THEN doSomething ELSE doOtherThing
Multi-line IF:
IF x > 0 AND x < 10 THEN
'do stuff
ELSE IF x = 0 THEN
'do other stuff
ELSE
'do more stuff
END IF
Like in C, any non-zero value is interpreted as True:
IF aNumber THEN
'the number is not 0
ELSE
'the number is 0
END IF
[edit] select case
Works with: QuickBasic version 4.5 Works with: FreeBASIC version 0.20.0 The condition in each case branch can be one or more constants or variables, a range or an expression.
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
[edit] 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
[edit] 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.
v > "X",@ non-zero
> & |
> "0",@ zero
# is the skip command. It unconditionally skips one character, allowing a little flexibility in flow control.
& #v_ "0",@ zero
> "X",@ non-zero
[edit] 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:
[.]
The . instruction will be skipped, while the following sequence
+[.]
will result in an infinite loop. Finally, in the following sequence
+[.-]
The . instruction will be executed once.
[edit] C
[edit] C++
[edit] Run-Time Control Structures
- See C
[edit] Compile-Time Control Structures
[edit] Preprocessor Techniques
- See C
[edit] Template metaprogramming
Selecting a type depending on a compile time condition
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
[edit] Clean
[edit] 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.
bool2int b = if b 1 0
[edit] case-of
case 6 * 7 of
42 -> "Correct"
_ -> "Wrong" // default, matches anything
[edit] function alternatives
answer 42 = True
answer _ = False
[edit] guards
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
[edit] Clojure
[edit] if-then-else
(if (= 1 1) :yes :no) ; returns :yes
(if (= 1 2) :yes :no) ; returns :no
(if (= 1 2) :yes) ; returns nil
[edit] 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.
(when x
(print "hello")
(println " world")
5) ; when x is logical true, prints "hello world" and returns 5; otherwise does nothing, returns nil
[edit] 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.
(cond
(= 1 2) :no) ; returns nil
(cond
(= 1 2) :no
(= 1 1) :yes) ; returns :yes
Since non-nil objects are logical true, by convention the keyword :else is used to yield a default result.
(cond
(= 1 2) :no
:else :yes) ; returns :yes
[edit] condp
Similar to cond, but useful when each test differs by only one variant.
(condp < 3
4 :a ; cond equivalent would be (< 4 3) :a
3 :b
2 :c
1 :d) ; returns :c
Optionally takes a final arg to be used as the default result if none of the tests match.
(condp < 3
4 :a
3 :b
:no-match) ; returns :no-match
[edit] case
Works with: Clojure version 1.2
(case 2
0 (println "0")
1 (println "1")
2 (println "2")) ; prints 2.
[edit] COBOL
[edit] if-then-else
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
[edit] evaluate
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
[edit] ColdFusion
[edit] if-elseif-else
Compiler: ColdFusion any version
<cfif x eq 3>
do something
<cfelseif x eq 4>
do something else
<cfelse>
do something else
</cfif>
[edit] switch
Compiler: ColdFusion any version
<cfswitch expression="#x#">
<cfcase value="1">
do something
</cfcase>
<cfcase value="2">
do something
</cfcase>
<cfdefaultcase>
do something
</cfdefaultcase>
</cfswitch>
[edit] Common Lisp
There are 2 main conditional operators in common lisp, (if ...) and (cond ...).
[edit] (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.
(if (= val 42)
"That is the answer to life, the universe and everything"
"Try again") ; the else clause here is optional
[edit] 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.
[edit] (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.
(cond ((= val 1) (print "no"))
((and (> val 3) (< val 6)) (print "yes"))
((> val 99) (print "too far"))
(T (print "no way, man!")))
[edit] C#
[edit] if-elseif-else
if (condition)
{
// Some Task
}
if (condition)
{
// Some Task
}
else if (condition2)
{
// Some Task
}
else
{
// Some Task
}
[edit] Ternary
// if condition is true var will be set to 1, else false.
int var = condition ? 1 : 2;
[edit] switch
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;
}
If fall through algorithms are required use the goto keyword.
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;
}
[edit] D
- See C, sans the preprocessor.
Compile-time check:
const i = 5; static if (i == 7) { ... } else { ... }
Compile-time type check:
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 {
...
}
[edit] Dao
[edit] If Elif Else
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' )
}
[edit] Switch Case
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' )
}
[edit] Delphi
- See Pascal
[edit] E
[edit] if-then-else
if (okay) {
println("okay")
} else if (!okay) {
println("not okay")
} else {
println("not my day")
}
The pick/2 message of booleans provides a value-based conditional:
println(okay.pick("okay", "not okay"))
It can therefore be used to construct a Smalltalk-style conditional:
okay.pick(fn {
println("okay")
}, fn {
println("not okay")
})()
All of the above conditionals are expressions and have a usable return value.
[edit] switch
E's "switch" allows pattern matching.
def expression := ["+", [1, 2]]
def value := switch (expression) {
match [`+`, [a, b]] { a + b }
match [`*`, [a, b]] { a * b }
match [op, _] { throw(`unknown operator: $op`) }
}
[edit] 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
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))
}
[edit] 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.
[edit] ?
? is for when you don't need branching, but only need to select between two different values.
t 1 2 ? ! returns 1
[edit] if
t [ 1 ] [ 2 ] if ! returns 1
[edit] cond
{ { [ t ] [ 1 ] } { [ f ] [ 2 ] } } cond ! returns 1
[edit] case
t { { t [ 1 ] } { f [ 2 ] } } case ! returns 1
[edit] when
t [ "1" print ] when ! prints 1
[edit] unless
f [ "1" print ] unless ! prints 1
[edit] FALSE
condition[body]?
Because there is no "else", you need to stash the condition if you want the same effect:
$[\true\]?~[false]?
or
$[%true0~]?~[false]?
[edit] Forth
[edit] IF-ELSE
( condition ) IF ( true statements ) THEN
( condition ) IF ( true statements ) ELSE ( false statements ) THEN
example:
10 < IF ." Less than 10" ELSE ." Greater than or equal to 10" THEN
[edit] CASE-OF
( n -- ) CASE
( integer ) OF ( statements ) ENDOF
( integer ) OF ( statements ) ENDOF
( default instructions )
ENDCASE
example: a simple CASE selection
: test-case ( n -- )
CASE
0 OF ." Zero!" ENDOF
1 OF ." One!" ENDOF
." Some other number!"
ENDCASE ;
[edit] Execution vector
To obtain the efficiency of a C switch statement for enumerations, one needs to construct one's own execution vector.
: 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!
[edit] 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*:
[edit] IF-THEN-ELSE
ANSI FORTRAN 77 or later has an IF-THEN-ELSE structure:
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
[edit] SELECT-CASE
ISO Fortran 90 or later has a SELECT-CASE structure:
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
[edit] 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.
! 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
[edit] Haskell
[edit] if-then-else
fac x = if x==0 then
1
else x * fac (x - 1)
[edit] Guards
fac x | x==0 = 1
| x>0 = x * fac (x-1)
[edit] Pattern matching
fac 0 = 1
fac x = x * fac (x-1)
[edit] case statement
fac x = case x of 0 -> 1
_ -> x * fac (x-1)
[edit] 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
[edit] IDL
[edit] if-else
Basic if/then:
if a eq 5 then print, "a equals five" [else print, "a is something else"]
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:
if a eq 5 then begin
... some code here ...
endif [else begin
... some other code here ...
endelse]
[edit] case
case <expression> of
(choice-1): <command-1>
[(choice-2): <command-2> [...]]
[else: <command-else>]
endcase
(Or replace any of the commands with {begin..end} pairs)
[edit] switch
switch <expression> of
(choice-1): <command-1>
[(choice-2): <command-2> [...]]
[else: <command-else>]
endswitch
The switch will execute all commands starting with the matching result, while the case will only execute the matching one.
[edit] on_error
on_error label
Will resume execution at label when an error is encountered. on_ioerror is similar but for IO errors.
[edit] Icon and Unicon
All Icon and Unicon expressions, including control structures, yield results or signal failure.
[edit] if-then-else
The control structure evaluates expr1 if expr0 succeeds and expr2 if it fails.
if expr0 then
expr1
else
expr2
[edit] case-of
The first successful selection expression will select and evaluate the specific case.
case expr0 of {
expr1 : expr2
expr3 : expr4
default: expr5
}
Note that expr1 and expr3 are expressions and not constants and it is possible to write expressions such as:
case x of {
f(x) | g(x) : expr2
s(x) & t(x) : expr4
default: expr5
}
[edit] Compound expressions (blocks)
In the examples below, multiple expressions can be grouped as in:
{
expr1
expr2
expr3
}
Which is equivalent to this:
{expr1; expr2; expr3}
For example the following, which will write 4, looks strange but is valid:
write({1;2;3;4})
The value of a compound expression is the value of the last expression in the block.
[edit] Alternation
Alternation of expressions yields a value for the first succeeding expression.
expr1 | expr2 | expr3
[edit] Conjunction
Conjunctions yeild the value of the final expression provided all the previous expressions succeed.
expr1 & expr2 & expr3
Alternately, conjunction can be written thus:
(expr1, expr2, expr3)
[edit] Conjunction, yielding a different result
The alternate form of conjunction can be modified to produce a different result (other than the last)
expr0(expr1, expr2, expr3)
For example:
2(expr1, expr2, expr3)
Yields the value of expr2 if all of the expressions succeed.
A more complicated example showing non-constant expressions:
f(expr1)(g(expr2)(expr3,expr4,expr5))
Note: if expr0 yields a value of type 'procedure' or 'string' the appropriate procedure (or operator) is invoked.
[edit] J
[edit] Java
[edit] if-then-else
if(s.equals("Hello World"))
{
foo();
}
else if(s.equals("Bye World"))
bar();//{}'s optional for one-liners
else
{
deusEx();
}
Java also supports short-circuit evaluation. So in a conditional like this:
if(obj != null && obj.foo()){
aMethod();
}
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:
if(obj != null & obj.foo()){
aMethod();
}
You will get a null pointer exception if obj is null.
[edit] ternary
s.equals("Hello World") ? foo() : bar();
[edit] 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.
switch(c) {
case 'a':
foo();
break;
case 'b':
bar();
default:
foobar();
}
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:
if(c == 'a'){
foo();
}else if(c == 'b'){
bar();
foobar();
}else{
foobar();
}
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).
[edit] JavaScript
[edit] if-then-else
if( s == "Hello World" ) {
foo();
} else if( s == "Bye World" ) {
bar();
} else {
deusEx();
}
[edit] switch
switch(object) {
case 1:
one();
break;
case 2:
case 3:
case 4:
twoThreeOrFour();
break;
case 5:
five();
break;
default:
everythingElse();
}
[edit] conditional (ternary) operator (?:)
var num = window.obj ? obj.getNumber() : null;
[edit] Lisaac
Works with: Lisaac version 0.13.1
[edit] if-then-else
+ 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";
};
(n = 2).if_true { "n is 2\n".print; };
(n = 2).if_false { "n is not 2\n".print; };
[edit] when
+ 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;
};
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.
[edit] Logo
if :x < 0 [make "x 0 - :x]
ifelse emptyp :list [print [empty]] [print :list]
UCBLogo and its descendants have also case:
to vowel? :letter
output case :letter [ [[a e i o u] "true] [else "false] ]
end
show vowel? "e
show vowel? "x
Output is:
true
false
Logo also provides TEST which is local to a procedure:
to mytest :arg1 :arg2
test :arg1 = :arg2
iftrue [print [Arguments are equal]]
iffalse [print [Arguments are not equal]]
end
[edit] LSE64
The simple conditionals take single words rather than blocks of statements, as in most other languages.
t : " true" ,t
f : " false" ,t
true if t
false ifnot f
true ifelse t f
Cascading conditionals are constructed using duplicate definitions and "then", yielding a syntax reminiscent of functional language Pattern Matching.
onetwo : drop " Neither one nor two" ,t # default declared first
onetwo : dup 2 = then " Two" ,t
onetwo : dup 1 = then " One" ,t
Short-circuit operators "&&" and "||" are used for complex conditionals.
dup 0 = || ,t # avoid printing a null string
[edit] lua
--if-then-elseif-then-else
if(a) then b()
elseif(c) then d()
else e()
end
for var = start, end, step do 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
[edit] Make
An if condition using pure make (no gmake extensions)
# 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."
Using it
make -f do.mk if C=0
> was false.
make -f do.mk if C=1
> was true.
With out using recursion but letting make continue with non-failed targets even when some of the targets failed (-k)
C=0
if: true false
true:
@expr $(C) >/dev/null && exit 0 || exit 1
@echo "was true."
false:
@expr $(C) >/dev/null && exit 1 || exit 0
@echo "was false."
Invoking it. Note the use of -k which allows make to evaluate subsequent targets even when a previous non-related target failed.
|make -f do.mk -s -k C=1
was true.
*** Error code 1
|make -f do.mk -s -k C=0
*** Error code 1
was false.
Using gmake
A=
B=
ifeq "$(A)" "1"
B=true
else
B=false
endif
do:
@echo $(A) .. $(B)
Using it
|gmake -f if.mk A=1
1 .. true
|gmake -f if.mk A=0
0 .. false
[edit] MATLAB
If statements
Example:
if x == 1
disp 'x==1';
elseif x > 1
disp 'x>1';
else
disp 'x<1';
end
Switch statements
Example:
switch x
case 1
disp 'Hello';
case 2
disp 'World';
otherwise
disp 'Skynet Active';
end
[edit] MAXScript
[edit] if
if x == 1 then
(
print "one"
)
else if x == 2 then
(
print "two"
)
else
(
print "Neither one or two"
)
[edit] case
Form one
case x of
(
1: (print "one")
2: (print "two")
default: (print "Neither one or two")
)
Form two
case of
(
(x == 1): (print "one")
(x == 2): (print "two")
default: (print "Neither one or two")
)
[edit] Metafont
if conditionA:
% do something
elseif conditionB:
% do something
% more elseif, if needed...
else:
% do this
fi;
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
b := if a > 5: 3 + else: 2 - fi c;
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.
[edit] Modula-3
[edit] if-then-else
IF Foo = TRUE THEN
Bar();
ELSE
Baz();
END;
IF Foo = "foo" THEN
Bar();
ELSIF Foo = "bar" THEN
Baz();
ELSIF Foo = "foobar" THEN
Quux();
ELSE
Zeepf();
END;
[edit] Case
CASE Foo OF
| 1 => IO.Put("One\n");
| 2 => IO.Put("Two\n");
| 3 => IO.Put("Three\n");
ELSE
IO.Put("Something\n");
END;
[edit] Type-case
TYPECASE is used on reference types to perform different operations, depending on what it is a reference to.
TYPECASE ref OF
| NULL => IO.Put("Null\n");
| CHAR => IO.Put("Char\n");
| INTEGER => IO.Put("Integer\n");
ELSE
IO.Put("Something\n");
END;
[edit] MUMPS
[edit] If / I
IF A GOTO Label
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:
IF T DO SUBROUTINE
ELSE DO SOMETHING
isn't clear because the function SUBROUTINE might change the value of $TEST.
[edit] $Select / $S
WRITE $SELECT(1=2:"Unequal",1=3:"More unequal",1:"Who cares?")
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.
[edit] :
SET:(1=1) SKY="Blue"
GOTO:ReallyGo LABEL
QUIT:LoopDone
WRITE:NotLastInSet ","
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.
[edit] newLISP
[edit] if
Interpreter: newLISP v.9.0
(set 'x 1)
(if (= x 1) (println "is 1"))
A third expression can be used as an else.
(set 'x 0)
(if (= x 1) (println "is 1") (println "not 1"))
[edit] Object Pascal
- See Pascal
[edit] 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".
[edit] OCaml
[edit] if-then-else
let condition = true
if condition then
1 (* evaluate something *)
else
2 (* evaluate something *)
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:
if condition then begin
(); (* evaluate things for side effects *)
5
end
else begin
(); (* evaluate things for side effects *)
42
end
[edit] match-with
match expression with
| 0 -> () (* evaluate something *)
| 1 -> () (* evaluate something *)
| n when n mod 2 = 0 -> () (* evaluate something *)
| _ -> () (* evaluate something *)
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.
[edit] Octave
if-then-elseif-else
if (condition)
% body
endif
if (condition)
% body
else
% otherwise body
endif
if (condition1)
% body
elseif (condition2)
% body 2
else
% otherwise body
endif
switch
switch( expression )
case label1
% code for label1
case label2
% code for label2
otherwise
% none of the previous
endswitch
Labels can be numeric or string, or cells to group several possibilities:
switch ( x )
case 1
disp("it is 1");
case { 5,6,7 }
disp("it is 5, or 6 or 7");
otherwise
disp("unknown!");
endswitch
[edit] Oz
[edit] if-then-else
proc {PrintParity X}
if {IsEven X} then
{Show even}
elseif {IsOdd X} then
{Show odd}
else
{Show 'should not happen'}
end
end
[edit] if-then-else as a ternary operator
fun {Max X Y}
if X > Y then X else Y end
end
[edit] case statement
fun {Fac X}
case X of 0 then 1
[] _ then X * {Fac X-1}
end
end
[edit] Pascal
[edit] if-then-else
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;
[edit] case
Works with: Turbo Pascal version 7.0
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.
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;
Given the variable "X" as a char the following is valid:
Case X of
'A' : statement ;
'B' : statement ;
in ['C'..'W'] : statement ;
else
Statement ;
end;
[edit] Perl
Works with: Perl version 5
[edit] 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;
};
[edit] 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.
[edit] 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;
[edit] logical operators
$condition and do_something is equivalent to $condition ? do_something : $condition.
$condition or do_something is equivalent to $condition ? $condition : do_something.
&& and || have the same semantics as and and or, respectively, but their precedence is much higher, making them better for conditional expressions than control flow.
[edit] switch
Works with: Perl version 5.10
use feature "switch";
given ($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; }
}
[edit] 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:if won() -> $prize {
If an
say "You won $prize.";
}elseblock 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:
$expression ?? do_something !! do_fallback
and, or, &&, and || work as in Perl 5.
[edit] PHP
[edit] if
Interpreter: PHP 3.x & 4.x & 5.x
<?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
}
?>
[edit] switch
Interpreter: PHP 3.x & 4.x & 5.x
<?php
switch ($i)
{
case "apple":
echo "i is apple";
break;
case "bar":
echo "i is bar";
break;
case "cake":
echo "i is cake";
break;
}
?>
[edit] See Also
[edit] PicoLisp
[edit] Two-way conditions
(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) )
One-way conditions
(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) )
[edit] Four-way condition
(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) )
[edit] Multiple conditions
(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) )
[edit] Selection
(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) ) )
[edit] Pop11
The simplest conditional is:
if condition then
;;; Action
endif;
Two way conditional looks like:
if condition then
;;; Action1
else
;;; Alternative action
endif;
One can do multiway choice using elseif clause
if condition1 then
;;; Action1
elseif condition2 then
;;; Action1
elseif condition2 then
;;; Action2
elseif condition3 then
;;; Action3
else
;;; Alternative action
endif;
Instead of if keyword one can use unless keyword.
unless condition then /* Action */ endunless;
has the same meaning as
if not(condition) then /* Action */ endif;
One can also use elseunless keword.
if condition1 then
;;; Action1
elseunless condition2 then
;;; Action2
endif;
;;; Action2
endif;
has the same meaning as
if condition1 then
;;; Action1
elseif not(condition2) then
;;; Action2
endif;
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:
if x > 0 then 1 elseif x < 0 then -1 else 0 endif -> sign_x ;
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).
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;
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:
#_IF condition1
/* Variant 1 */
#_ELSEIF condition2
/* Variant 2 */
#_ELSE
/* Variant 3 */
#_ENDIF
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.
[edit] 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):
9 10 lt {(9 is less than 10) show} if
The "ifelse" operator expects two procedures and executes the one or the other depending on the value of the boolean. I.e. this:
/a 5 lt {(yeah)} {(nope)} ifelse show
will render either the string "yeah" or "nope" depending on whether a is less than 5 or not.
[edit] PowerShell
[edit] If, ElseIf, Else
# standard if
if (condition) {
# ...
}
# if-then-else
if (condition) {
# ...
} else {
# ...
}
# if-then-elseif-else
if (condition) {
# ...
} elseif (condition2) {
# ...
} else {
# ...
}
[edit] Switch
# 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" }
}
[edit] PureBasic
Works with: PureBasic version 4.41
[edit] If, Elseif, Else
If a = 0
Debug "a = 0"
ElseIf a > 0
Debug "a > 0"
Else
Debug "a < 0"
EndIf
[edit] Select
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
[edit] 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.
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
[edit] CompilerSelect
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
[edit] Python
[edit] if-then-else
if x == 0:
foo()
elif x == 1:
bar()
elif x == 2:
baz()
else:
boz()
[edit] ternary expressions
Interpreter: Python 2.5
true_value if condition else false_value
Example:
secret='foo'
print 'got it' if secret=='foo' else 'try again'
'got it'
Note: this syntax is valid as an expression, the clauses cannot constain statements. The foregoing example is equivalent to:
secret = 'foo'
result = 'got it' if secret=='foo' else 'try again'
print result
'got it'
[edit] 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.
[edit] R
[edit] if-else
#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.
[edit] ifelse
#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)
[edit] switch
#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.
[edit] Rhope
Works with: Rhope version alpha 1
[edit] if-then-else
If[cond]
|:
Do Something[]
:||:
Do Something Else[]
:|
[edit] Ruby
See Conditional Structures/Ruby
[edit] Sather
if EXPR then
-- CODE
elsif EXPR then
-- CODE
else
-- CODE
end;
EXPR must evaluate to BOOL (true or false); elsif and else are optional.
case EXPR
when EXPRL then
-- CODE
when EXPRL then
-- CODE
else
-- CODE
end;
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)
[edit] Scheme
Procedures can be categorised as primitive or derived. Derived procedures can be defined in terms of primitive procedures.
[edit] Primitive
[edit] if
(if <test> <consequent> <alternate>)
(if <test> <consequent>)
Example:
(display
(if (> 1 2)
"yes"
"no"))
(newline)
(display
(if (> 1 2)
(- 1 2)))
(newline)
Output:
no
#<unspecified>
[edit] Derived
[edit] cond
(cond <clause1> <clause2> ...)
Example:
(display
(cond ((> 1 2) "greater")
((< 1 2) "less")))
(newline)
(display
(cond ((> 1 1) "greater")
((< 1 1) "less")
(else "equal")))
(newline)
Output:
less
equal
[edit] case
(case <key> <clause1> <clause2> ...)
Example:
(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)
Output:
composite
consonant
[edit] Slate
[edit] ifTrue/ifFalse
"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!'.].
[edit] caseOf:otherwise:
c@(Net URLPathEncoder traits) convert
[ | byte1 byte2 byte3 digit1 digit2|
[c in isAtEnd] whileFalse:
[byte1: c in next.
byte1 caseOf: {
$+ -> [c out nextPut: $\s].
$% -> [byte2: c in next.
byte3: c in next.
digit1: (byte2 toDigit: 16).
digit2: (byte3 toDigit: 16).
digit1 isNil \/ [digit2 isNil] ifTrue: [error: 'Error reading hex sequence after %'].
c out nextPut: (digit1 * 16 + digit2 as: c out elementType)].
} otherwise: [c out nextPut: byte1].
].
].
[edit] whileTrue:/whileFalse:
[p isAtEnd] whileFalse: [p next evaluate]].
[edit] SIMPOL
[edit] if-else if-else
if x == 1
foo()
else if x == 2
bar()
else
foobar()
end if
[edit] ternary if function
.if(x == 1, "hello", "world")
[edit] Smalltalk
The pattern for handling a multi-option switch is to create classes for the various options, and let Polymorphism take care of the decisions.
[edit] ifTrue/ifFalse
"Conditionals in Smalltalk are really messages sent to Boolean objects"
balance > 0
ifTrue: [Transcript cr; show: 'still sitting pretty!'.]
ifFalse: [Transcript cr; show: 'No money till payday!'.].
You can also use them as the ternary operator
abs := x > 0 ifTrue: [ x ] ifFalse: [ x negated ]
[edit] SNOBOL4
SNOBOL4 has no structured programming features, but the two constructs in question could be easily emulated with FAILURE/SUCCESS and indirect jumps
A = "true"
* "if-then-else"
if A "true" :s(goTrue)f(goFalse)
goTrue output = "A is TRUE" :(fi)
goFalse output = "A is not TRUE" :(fi)
fi
* "switch"
switch A ("true" | "false") . switch :s($("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
[edit] SNUSP
$==?\==zero=====!/==#
\==non zero==/
? 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.
[edit] SQL
Works with: MS SQL version 2005
[edit] Conditional Expression
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
[edit] If/Else
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'
[edit] Tcl
[edit] if-then-else
if {$foo == 3} {
puts "foo is three"
} elseif {$foo == 4} {
puts "foo is four"
} else {
puts "foo is neither three nor four"
}
or (using the ternary operator of expressions)
set result [expr { $foo == 3 ? "three" : "not three" }]
[edit] switch
switch -- $foo {
3 {puts "foo is three"}
4 {puts "foo is four"}
default {puts "foo is something else"}
}
Note that the switch command can also use glob matching (like case in the Bourne Shell) or regular-expression matching.
[edit] Toka
[edit] ifTrue
( condition ) ( quote ) ifTrue
100 100 = [ ." True\n" ] ifTrue
100 200 = [ ." True\n" ] ifTrue
[edit] ifFalse
( condition ) ( quote ) ifFalse
100 100 = [ ." True\n" ] ifFalse
100 200 = [ ." True\n" ] ifFalse
[edit] ifTrueFalse
( condition ) ( true quote ) ( false quote ) ifTrueFalse
100 100 = [ ." Equal\n" ] [ ." Not Equal\n" ] ifTrueFalse
100 200 = [ ." Equal\n" ] [ ." Not Equal\n" ] ifTrueFalse
[edit] Trith
[edit] branch
true ["yes" print] ["no" print] branch
[edit] when
true ["yes" print] when
[edit] unless
false ["no" print] unless
[edit] V
[edit] ifThenElse
[true]
['is true' puts]
['is false' puts]
ifte
=is true
[edit] ifThen
[true]
['is true' puts]
if
=is true
[edit] When
3 [
[1 =] [1 *]
[2 =] [10 *]
[3 =] [100 *]
[4 =] [1000 *]
] when
=300
[edit] Choice
true
1 2
choice
=1
false
1 2
choice
=2
[edit] VBScript
[edit] if-then-else
if (condition) then
result = "met"
else
Result = "not met"
end if
[edit] Visual Basic .NET
[edit] if-then-else
Basic
Dim result As String, a As String = "pants", b As String = "glasses"
If a = b Then
result = "passed"
Else
result = "failed"
End If
Condensed
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
[edit] if-then-elseif
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
[edit] select-case-else
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
[edit] inline-conditional
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
[edit] generic-inline-conditional
Works with: Microsoft (R) Visual Basic Compiler version 8.0
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
[edit] generic-inline-conditional
Language Version: 9.0+
Dim result As String = If("pants" = "glasses", "passed", "failed") ' type is inferred
[edit] Vorpal
[edit] if-then-else
if(condition){
result = 'met'
}
else{
result = 'not met'
}
[edit] Wrapl
[edit] simple conditional
Conditionals in Wrapl are expressions. Either success or failure can be omitted from the expression.
condition => success // failure
condition => success
condition // failure
[edit] 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.
condition & success
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.
condition | failure
[edit] XSLT
The <xsl:if> element allows simple conditional processing.
<xsl:if test="condition">
<!-- executed if XPath expression evaluates to true -->
</xsl:if>
The <xsl:choose>, <xsl:when>, and <xsl:otherwise> elements allow more general conditional processing.
<xsl:choose>
<xsl:when test="condition1">
<!-- executed if condition1 evaluates to true -->
</xsl:when>
<xsl:when test="condition2">
<!-- executed if condition2 evaluates to true -->
</xsl:when>
<-- etc. -->
<xsl:otherwise>
<!-- optional catch-all processing, like C's else or default -->
</xsl:otherwise>
</xsl:choose>
The XPath expressions allowed for the "test" attribute are those which return a boolean value:
@attrib = 'false'
position() != last()
not( false() )
boolean( $param )
contains( node, "stuff" ) and (position() > first())
