Control Structures

Control Structures
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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.

This page is being split into multiple articles. Please help move code into these articles, instead:

• Conditional Structures
• Flow Control Structures
• Loop Structures
• Exceptions

Conditional

These control structures depend on conditions to control their behavior.

Python

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()

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

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();
   }

do-while

   do
   {
       foo();
   }
   while (true)

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();
   }

SmallTalk

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!'.].

whileTrue/whileFalse

 x := 0.
 [ x < 100 ]
      whileTrue: [ x := x + 10.].

 [ x = 0 ]
      whileFalse: [ x := x - 20.].

Iterative

These control structure operate on datasets.

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++

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) {
   // ...
 }

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

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