Control Structures

From Rosetta Code
Task
Control Structures
You are encouraged to solve this task according to the task description, using any language you may know.

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

These control structures depend on conditions to control their behavior.

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++

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

  1. ifdef, #ifndef, etc..

Template Metaprogramming Techniques

Template metaprogramming techniques.

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

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

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

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

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

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;
}


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

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

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();
   }

Iterative

These control structure operate on datasets.

C++

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

foreach

Platform: J2SE 1.5.0 

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

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


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

for

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

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

foreach

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

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
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