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

ifdef, #ifndef, etc..

Template Metaprogramming Techniques

Template metaprogramming techniques.

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
}

#!/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
}

unless

Interpreter: Perl 5.8.8

#!/usr/bin/perl -w

use strict;

my $condition1 = 0;

unless ( $condition1 ) {
  # Do something
}

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 );

for

Interpreter: Perl 5.8.8

#!/usr/bin/perl -w

use strict;

my $limit = 5;

for ( my $iterator = 0; $iterator < $limit; $iterator++ ) {
  # Do something
}

Python

if-then-else

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

while

while ok():
    foo()
    bar()
    baz()

for

for i in range(10):
    print i

try-except-else

try:
   foo()
except TypeError:
   bar()
else:
   baz()

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;
}

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();
   }

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

foreach

Interpreter: Perl 5.8.8

#!/usr/bin/perl -w

use strict;

my @array = ("Value1", "Value2", "Value3", "Value4", "Value5");

foreach ( @array ) {
  my $item = $_
  # Do something with $_.
}

Python

for

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

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