Control Structures: Difference between revisions

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[[Category:Encyclopedia]]'''Control structures''' are features of programming languages that influence the code flow. Examples of control structures are:
{{task}}
*loops, which repeat sections of code
*conditions, which selectively execute sections of code
*exceptions, which help in error handling and avoid causing more problems when there is another problem
*jumps (a.k.a. "branches" or "gotos"), which explicitly and usually unconditionally set the next instruction to be executed by the program


Examples of these structures can be found on the following pages:
Control structures are features of programming languages that influence the code flow. Two common examples are loops and conditions. The task here is to demonstrate control structures supported by different programming languages.


=Conditional=
* [[Conditional Structures]]
* [[Flow Control Structures]]

* [[Loop Structures]]
These control structures depend on conditions to control their behavior.
* [[Exceptions]]

* [[Help:Orphaned code]]
==[[AppleScript]]==
[[Category:AppleScript]]
===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

===repeat-until===
set i to 5
repeat until i is less than 0
set i to i - 1
end repeat

repeat
--endless loop
end repeat


==[[C]]==
[[Category:C]]
===if-then-else===
'''Compiler:''' [[GCC]] 4.1.2
int main (int argc, char ** argv) {
int input = 2;
if ( 3 == input ) {
// Do something
}
if ( 3 == input ) {
// Do something
} else {
// Do something else
}
}

===switch===
'''Compiler:''' [[GCC]] 4.1.2
int main (int argc, char ** argv) {
int input = 42;
switch (input) {
case 0:
// Do something, because input = 0
break;
case 1:
// Do something, because input = 1
break;
case 2:
// Do something, because input = 2
default:
// Do something else.
break; // Optional
}
}

===while===
'''Compiler:''' [[GCC]] 4.1.2
int main (int argc, char ** argv) {
int condition = 1;
while ( condition ) {
// Do something
// Don't forget to change the value of condition.
// If it remains nonzero, we'll have an infinite loop.
}
}

===do-while===
'''Compiler:''' [[GCC]] 4.1.2
int main (void) {
int condition = 1;
do {
// Do something
// Don't forget to change the value of condition.
// If it remains nonzero, we'll have an infinite loop.
} while ( condition );
}

==[[C plus plus|C++]]==
[[Category:C plus plus]]
=== Run-Time Control Structures ===

==== for ====
'''Compiler:''' [[GCC]] 3.3.4
#include <iostream>
int main()
{
int i = 1;
// Loops forever:
for(; i == 1;)
std::cout << "Hello, World!\n";
}

==== goto ====
'''Compiler:''' [[GCC]] 3.3.4
#include <iostream>
int main()
{
LOOP:
std::cout << "Hello, World!\n";
goto LOOP;
}

Note that this may also be used in conjunction with other forms of branching.

====if-then-else====
'''Compiler:''' [[GCC]] 4.1.2
int main (void) {
int input = 2;
if ( 3 == input ) {
// Do something
}



if ( 3 == input ) {
// Do something
} else {
// Do something else
}
}

====switch====
'''Compiler:''' [[GCC]] 4.1.2

int main (void) {
int input = 42;
switch (input) {
case 0:
// Do something, because input = 0
break;
case 1:
// Do something, because input = 1
break;
case 2:
// Do something, because input = 2
default:
// Do something else.
break; // Optional
}
}

====while====
'''Compiler:''' [[GCC]] 4.1.2
int main (void) {
int condition = 1;
while ( condition ) {
// Do something
// Don't forget to change the value of condition.
// If it remains nonzero, we'll have an infinite loop.
}
}

====do-while====
'''Compiler:''' [[GCC]] 4.1.2
int main (void) {
int condition = 1;
do {
// Do something
// Don't forget to change the value of condition.
// If it remains nonzero, we'll have an infinite loop.
} while ( condition );
}

=== Compile-Time Control Structures ===

==== Preprocessor Techniques ====

#ifdef, #ifndef, etc..

==== Template Metaprogramming Techniques ====

Template metaprogramming techniques.

==[[ColdFusion]]==
[[Category:ColdFusion]]
===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>

===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>

==[[OCaml]]==
[[Category:OCaml]]
===if-then-else===
'''Compiler:''' [[OCaml]] 3.09
let condition = true
if condition then
()//do something
else
()//do something else

===match-with===
match expression with
| 0 -> ()//do something
| 1 -> ()//do something
| n when n mod 2 = 0 -> ()//do something
| _ -> ()//do something

==[[Pascal]]==
[[Category:Pascal]]
===if-then-else===
'''Compiler:''' [[Turbo Pascal]] 7.0
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;

===while===

'''Compiler:''' [[Turbo Pascal]] 7.0

WHILE condition1 DO
BEGIN
procedure1;
procedure2;
END;

===do-while===

'''Compiler:''' [[Turbo Pascal]] 7.0
DO
BEGIN
procedure1;
procedure2;
END
WHILE condition1;

===for===

'''Compiler:''' [[Turbo Pascal]] 7.0

FOR counter=1 TO 10 DO
BEGIN
procedure1;
procedure2;
END;

==[[Perl]]==
[[Category:Perl]]
===if-then-else===
'''Interpreter:''' [[Perl]] 5.8.8
#!/usr/bin/perl -w
use strict;
my $condition1 = 0;
my $condition2 = 1;
if ( $condition1 ) {
# Do something
}
# post-conditional if
do_something() if $condition1;


#!/usr/bin/perl -w
use strict;
my $condition1 = 0;
my $condition2 = 1;
if ( $condition1 ) {
# Do something
} elsif ( $condition2 ) {
# Do somethine else
}


#!/usr/bin/perl -w
use strict;
my $condition1 = 0;
my $condition2 = 1;
if ( $condition1 ) {
# Do something
} else {
# Do something else
}


#!/usr/bin/perl -w
use strict;
my $condition1 = 0;
my $condition2 = 1;
if ( $condition1 ) {
# Do something
} elsif ( $condition2 ) {
# Do something else
} else {
# Do that other thing
}

($condition) ? print "Then\n" : print "Else\n";
# or
my $var = ($condition) ? "Then" : "Else";

===unless===

'''Interpreter:''' [[Perl]] 5.8.8
#!/usr/bin/perl -w
use strict;
my $condition1 = 0;
unless ( $condition1 ) {
# Do something
}

# post-conditional unless
do_something() unless $condition1;
unless ( $condition1 ) {
# Do something
} else {
# Do something else
}

===while===

'''Interpreter:''' [[Perl]] 5.8.8
#!/usr/bin/perl -w
use strict;
my $condition1 = 0;
while ( $condition1 ) {
# Do something.
# Remember to change the value of condition1 at some point.
}

===do-while===

'''Interpreter:''' [[Perl]] 5.8.8
#!/usr/bin/perl -w
use strict;
my $condition1 = 0;
do {
# Do something.
# Remember to change the value of condition1 at some point.
} while ( $condition1 );
===until===

'''Interpreter:''' [[Perl]] 5.8.8
#!/usr/bin/perl -w
use strict;
my $condition1 = 1;
until ( $condition1 ) {
# Do something.
# Remember to change the value of condition1 at some point.
}


===do-until===
'''Interpreter:''' [[Perl]] 5.8.8

#!/usr/bin/perl -w
use strict;
my $condition1 = 1;
do {
# Do something.
# Remember to change the value of condition1 at some point.
} until ( $condition1 );

===switch===
'''Interpreter:''' [[Perl]] 5.8.8

#!/usr/bin/perl -w
use strict;
use Switch;
$input = 42;
switch ($input) {
case 0 {
# Do something, because input = 0
}
case 1 {
# Do something, because input = 1
}
case "coffee" {
# Do something, because input = coffee
}
else {
# Do something else.
}
}

===goto===
'''Interpreter:''' [[Perl]] 5.8.8

Typically dispised by most Perl programmers

goto LABELB;
LABELA: # note labels end with a colon not semi-colon
goto END;
LABELB:
goto LABELA;
END:
exit(0);

==[[Python]]==
[[Category:Python]]
===if-then-else===

if x == 0:
foo()
elif x == 1:
bar()
elif x == 2:
baz()
else:
boz()

===while===

while ok():
foo()
bar()
baz()
else:
# break was not called
quux()

===for===

for i in range(10):
print i
else:
# break was not called
foo()


===try-except-finally-else===

'''Interpreter''': Python 2.5

Before Python 2.5 it was not possible to use finally and except together.

try:
foo()
except TypeError:
bar()
finally:
baz()
else:
# no exception occurred
quux()


===with===

'''Interpreter''': Python 2.5

foo could for example open a file or create a lock or a database transaction:

with foo() as bar:
baz(bar)

==[[PHP]]==
[[Category:PHP]]
===if-then-else===

if ($x == 0) {
foo();
} else if ($x == 1) {
bar();
} else if ($x == 2) {
baz();
} else {
boz();
}

===while===

while(ok()) {
foo();
bar();
baz();
}
===for===

for($i = 0; $i < 10; ++$i) {
echo $i;
}

===foreach===

foreach(range(0, 9) as $i) {
echo $i;
}
===switch===
switch($c)
{
case 'a':
foo();
break;
case 'b':
bar();
default:
foobar();
}

==[[Ruby]]==
[[Category:Ruby]]
===if-then-else===

if s == 'Hello World'
foo
elsif s == 'Bye World'
bar
else
deus_ex
end

===while===

while true do
foo
end

===for===

for i in [0..4] do
foo
end

===case-when-else===

case cartoon_character
when 'Tom'
chase
when 'Jerry'
flee
else
nil
end

===ternary===

s == 'Hello World' ? foo : bar

==[[Java]]==
[{Category:Java]]
===if-then-else===

if(s.equals("Hello World"))
{
foo();
}
else if(s.equals("Bye World"))
{
bar();
}
else
{
deusEx();
}

===while===

while(true)
{
foo();
}
===for===

for(int i = 0; i < 5; i++)
{
foo();
}

===ternary===

s.equals("Hello World") ? foo : bar

===switch===
switch(c) {
case 'a':
foo();
break;
case 'b':
bar();
default:
foobar();
}

==[[JavaScript]]==
[[Category:JavaScript]]
===if-then-else===

if(s=="Hello World")
{
foo();
}
else if(s=="Bye World")
{
bar();
}
else
{
deusEx();
}

===while===

while(true)
{
foo();
}
===for===

for(var i = 0; i < 5; i++)
{
foo();
}

==[[SmallTalk]]==
[[Category: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!'.].

=Iterative=

These control structure operate on datasets.

==[[AppleScript]]==
[[Category:AppleScript]]
===repeat-with===
repeat with i from 1 to 20
--do something
end repeat

set array to {1,2,3,4,5}
repeat with i in array
display dialog i
end repeat

==[[C plus plus|C++]]==
[[Category:C plus plus]]
===for_each ===
'''Compiler:''' [[GCC]] 4.1.1

#include <iostream> // std::cout, std::endl
#include <vector> // std::vector
#include <algorithm> // std::for_each
struct sum
{
int _sum;
sum() : _sum(0) {}; // Initialize sum with 0;
void operator() (int a) { _sum += a; } // this function will be called for every element
};
int main()
{
std::vector<int> v;
v.push_back(10);
v.push_back(23);
v.push_back(34);
/* Note that for_each gets a fresh instance of sum passed,
* applies every element beginning with *v.begin() up to,
* but not including v.end() to the function object
* and returns a copy of it.
*/
sum the_sum = std::for_each(v.begin(), v.end(), sum());
std::cout << "The sum is " << the_sum._sum << std::endl;
return 0;
}

==[[Java]]==
[[Category:Java]]
===foreach===
'''Platform:''' [[J2SE]] 1.5.0

Object[] objects;
// ...
for (Object current : objects[]) {
// ...
}

int[] numbers;
// ...
for (int i : numbers) {
// ...
}


==[[Javascript]]==
[[Category:Javascript]]
===foreach===

//iterate through properties of an object as if through a collection
var obj = {prop1:"a",prop2:"b",prop3:"c"};
for (var key in obj)
alert(obj[key]);


==[[Perl]]==
[[Category:Perl]]
===for===
'''Interpreter:''' [[Perl]] 5.8.8

#!/usr/bin/perl -w
use strict;
my $limit = 5;
for ( my $iterator = 0; $iterator < $limit; $iterator++ ) {
# Do something
}
# for-variant, implicit iteration
for (0..$limit) {
# Do something
}
do_something() for 0..$limit;

===foreach===
'''Interpreter:''' [[Perl]] 5.8.8

#!/usr/bin/perl -w
use strict;
my @numbers = (1, 2, 3);
my %names = (first => "George", last => "Jetson");
foreach my $number (@numbers) {
# Do something with $number
}
foreach my $key (keys %names) {
# Do something with $key (values are accessible as %names{$key} )
}

===map===
'''Interpreter:''' [[Perl]] 5.8.8

#!/usr/bin/perl -w
use strict;
my @numbers = (1, 2, 3);
my @target;
@target = map {
# Do something with $_
} @numbers;
@target = map($_ + 1, @numbers);
sub a_sub {
# Do something with $_
}
@target = map a_sub @numbers;

===grep===
'''Interpreter:''' [[Perl]] 5.8.8

#!/usr/bin/perl -w
use strict;
my @people = qw/Bobbie Charlie Susan/;
my @target;
@target = grep {
# Discriminate based on $_
} @people;
# Feed grep into map, this picks out elements 1, 3, 5, etc.
@target = map($people[$_], grep($_ & 1, 0..$#people));
# Pick out the diminutive names
@target = grep(/ie$/, @people);
sub a_sub {
# Do something with $_, and return a true or false value
}
@target = grep a_sub @people;

==[[Python]]==
[[Category:Python]]
=== for ===

for x in ["foo", "bar", "baz"]:
print x



==[[Ruby]]==
[[Category:Ruby]]
=== each ===

['foo', 'bar', 'baz'].each do |x|
puts x
end

=== collect ===

array = ['foo', 'bar', 'baz'].collect do |x|
foo x
end

=== map ===

array = ['foo', 'bar', 'baz'].map {|x| foo x }

=== inject ===

string = ['foo', 'bar', 'baz'].inject("") do |s,x|
s << x
s
end

sum = ['foo', 'bar', 'baz'].inject(0) do |s,x|
s + x.size
s
end

product = ['foo', 'bar', 'baz'].inject(1) do |p,x|
p * x.size
p
end

hash = ['foo', 'bar', 'baz'].inject({}) do |h,x|
h[x] = x.size
h
end

boolean = ['foo', 'bar', 'baz'].inject(true) do |b,x|
b &&= x != 'bar'
b
end

==[[Tcl]]==
[[Category:Tcl]]
=== foreach ===

foreach i {foo bar baz} {
puts "$i"
}

==[[UNIX Shell]]==
[[Category:UNIX Shell]]
===for===
'''Interpreter:''' [[Bourne Again SHell]]

#!/bin/bash
ARRAY="VALUE1 VALUE2 VALUE3 VALUE4 VALUE5"
for ELEMENT in $ARRAY
do
echo $ELEMENT # Print $ELEMENT
done

'''Interpreter:''' [[Debian Almquist SHell]]

#!/bin/sh
ARRAY="VALUE1 VALUE2 VALUE3 VALUE4 VALUE5"
for ELEMENT in $ARRAY
do
echo $ELEMENT # Print $ELEMENT
done

Latest revision as of 20:37, 22 October 2008

Control structures are features of programming languages that influence the code flow. Examples of control structures are:

  • loops, which repeat sections of code
  • conditions, which selectively execute sections of code
  • exceptions, which help in error handling and avoid causing more problems when there is another problem
  • jumps (a.k.a. "branches" or "gotos"), which explicitly and usually unconditionally set the next instruction to be executed by the program

Examples of these structures can be found on the following pages:

Retrieved from "https://rosettacode.org/wiki/Control_Structures?oldid=359"