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 (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 );

}

C++

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 );
}

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

Iterative

These control structure operate on datasets.

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

for

for {set i 0} {$i < 3} {incr i} {
    puts "$i"
}

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