PHP 7.0.14 Released

do-while

(PHP 4, PHP 5, PHP 7)

Les boucles do-while ressemblent beaucoup aux boucles while, mais l'expression est testée à la fin de chaque itération plutôt qu'au début. La principale différence par rapport à la boucle while est que la première itération de la boucle do-while est toujours exécutée (l'expression n'est testée qu'à la fin de l'itération), ce qui n'est pas le cas lorsque vous utilisez une boucle while (la condition est vérifiée dès le début de chaque itération, et si elle s'avère FALSE dès le début, la boucle sera immédiatement arrêtée).

Il n'y a qu'une syntaxe possible pour les boucles do-while :

<?php
$i 
0;
do {
    echo 
$i;
} while (
$i 0);
?>

La boucle ci-dessus ne va être exécutée qu'une seule fois, car lorsque l'expression est évaluée, elle vaut FALSE (car la variable $i n'est pas plus grande que 0) et l'exécution de la boucle s'arrête.

Les utilisateurs familiers du C sont habitués à une utilisation différente des boucles do-while , qui permet de stopper l'exécution de la boucle au milieu des instructions, en encapsulant dans un do-while(0) la fonction break. Le code suivant montre une utilisation possible :

<?php
do {
    if (
$i 5) {
        echo 
"i n'est pas suffisamment grand";
        break;
    }
    
$i *= $factor;
    if (
$i $minimum_limit) {
        break;
    }
   echo 
"i est bon";

    
/* ...traitement de i... */

} while (0);
?>

Ne vous inquiétez pas si vous ne comprenez pas tout correctement. Vous pouvez écrire des scripts très très puissants sans utiliser cette fonctionnalité. Depuis PHP 5.3.0, il est possible d'utiliser l'opérateur goto à l'intérieur de cette fonctionnalité.

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User Contributed Notes 6 notes

up
18
Martin
1 year ago
Do-while loops can also be used inside other loops, for example:

<?php
// generating an array with random even numbers between 1 and 1000

$numbers = array();
$array_size = 10;

// for loop runs as long as 2nd condition evaluates to true
for ($i=0;$i<$array_size;$i++) {

     
// always executes (as long as the for-loop runs)
     
do {
        
$random = rand(1,1000);

    
// if the random number is even (condition below is false), the do-while-loop execution ends
     // if it's uneven (condition below is true), the loop continues by generating a new random number
    
} while (($random % 2) == 1);

    
// even random number is written to array and for-loop continues iteration until original condition is met
    
$numbers[] = $random;
}

// sorting array by alphabet

asort($numbers);

// printing array

echo '<pre>';
print_r($numbers);
echo
'</pre>';
?>
up
11
jayreardon at gmail dot com
9 years ago
There is one major difference you should be aware of when using the do--while loop vs. using a simple while loop:  And that is when the check condition is made. 

In a do--while loop, the test condition evaluation is at the end of the loop.  This means that the code inside of the loop will iterate once through before the condition is ever evaluated.  This is ideal for tasks that need to execute once before a test is made to continue, such as test that is dependant upon the results of the loop. 

Conversely, a plain while loop evaluates the test condition at the begining of the loop before any execution in the loop block is ever made. If for some reason your test condition evaluates to false at the very start of the loop, none of the code inside your loop will be executed.
up
1
fuhse at data-quest dot de
4 days ago
What actually surprised me: There is no alternative-syntax or template syntax for a do-while-loop.

So you can write

<?php
while ($a < 10) :
   
$a++;
endwhile;
?>

But this won't work:

<?php
do :
   
$a++
while (
$a <= 10);
?>
up
-4
jaysherby at gmail dot com
4 months ago
The last example on this page is simply abuse of the `break` keyword.  Also, the suggestion to use `goto` if you don't understand the abuse of `break` is unsettling.  (See the manual page for `goto` for more than enough reasons not to use it.)

The final example is generally better expressed using a typical if-else statement.

<?php
if ($i < 5) {
    echo
"i is not big enough";
} else {
   
$i *= $factor;

    if (
$i >= $minimum_limit) {
      echo
"i is ok";

     
/* process i */
   
}
}
?>

This version is easier to read and understand.  And arguments for code golf are invalid as well as this version is 3 lines shorter.

In conclusion, although you can certainly write code that abuses the `break` keyword, you shouldn't in practice.  Keep the code easy to read and understand for whoever inherits your code.  And remember, code is for humans not computers.
up
-13
shaida dot mca at gmail dot com
6 years ago
Example of Do while :-

<?php
$i
= 0;
echo
'This code will run at least once because i default value is 0.<br/>';
do {
echo
'i value is ' . $i . ', so code block will run. <br/>';
++
$i;
} while (
$i < 10);
?>
up
-16
andrew at NOSPAM dot devohive dot com
8 years ago
I'm guilty of writing constructs without curly braces sometimes... writing the do--while seemed a bit odd without the curly braces ({ and }), but just so everyone is aware of how this is written with a do--while...

a normal while:
<?php
  
while ( $isValid ) $isValid = doSomething($input);
?>

a do--while:
<?php
  
do $isValid = doSomething($input);
   while (
$isValid );
?>

Also, a practical example of when to use a do--while when a simple while just won't do (lol)... copying multiple 2nd level nodes from one document to another using the DOM XML extension

<?php
  
# open up/create the documents and grab the root element
  
$fileDoc  = domxml_open_file('example.xml'); // existing xml we want to copy
  
$fileRoot = $fileDoc->document_element();
  
$newDoc   = domxml_new_doc('1.0'); // new document we want to copy to
  
$newRoot  = $newDoc->create_element('rootnode');
  
$newRoot  = $newDoc->append_child($newRoot); // this is the node we want to copy to

   # loop through nodes and clone (using deep)
  
$child = $fileRoot->first_child(); // first_child must be called once and can only be called once
  
do $newRoot->append_child($child->clone_node(true)); // do first, so that the result from first_child is appended
  
while ( $child = $child->next_sibling() ); // we have to use next_sibling for everything after first_child
?>
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