The PHP Online Conference 2021

while

(PHP 4, PHP 5, PHP 7)

Laços while são os mais simples tipos de laços do PHP. Possui comportamento semelhante ao C. O formato básico de uma declaração while é:

while (expr)
    statement

O propósito da declaração while é simples. Ele dirá ao PHP para executar as declarações aninhadas repetidamente, enquanto a expressão do while forem avaliadas como TRUE. O valor da expressão é checado a cada vez que o laço é iniciado, então, mesmo seu valor mude durante a a execução das declarações aninhadas, a execução não será interrompida até o final da iteração ( cada vez que o PHP executa as declarações dentro do laço é uma iteração). Entretanto, se a expressão do while for avaliada como FALSE desde o início, as declarações aninhadas não serão executadas nenhuma vez.

Similar a declaração if, pode-se agrupar múltiplas declarações no mesmo laço while delimitando o grupo de declarações por chaves, ou utilizando a sintaxe alternativa:

while (expr):
    statement
    ...
endwhile;

Os exemplos a seguir são idênticos, e ambos imprimem os números de 1 a 10.

<?php
/* example 1 */

$i 1;
while (
$i <= 10) {
    echo 
$i++;  /* the printed value would be
                   $i before the increment
                   (post-increment) */
}

/* example 2 */

$i 1;
while (
$i <= 10):
    echo 
$i;
    
$i++;
endwhile;
?>

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User Contributed Notes 7 notes

up
-6
scott at mstech dot com
11 years ago
Just a note about using the continue statement to forego the remainder of a loop - be SURE you're not issuing the continue statement from within a SWITCH case - doing so will not continue the while loop, but rather the switch statement itself.

While that may seem obvious to some, it took a little bit of testing for me, so hopefully this helps someone else.
up
-29
chayes at antenna dot nl
18 years ago
At the end of the while (list / each) loop the array pointer will be at the end.
This means the second while loop on that array will be skipped!

You can put the array pointer back with the reset($myArray) function.

example:

<?php
$myArray
=array('aa','bb','cc','dd');
while (list (
$key, $val) = each ($myArray) ) echo $val;
reset($myArray);
while (list (
$key, $val) = each ($myArray) ) echo $val;
?>
up
-25
ravenswd at gmail dot com
10 years ago
I find it often clearer to set a simple flag ($finished) to false at the start of the loop, and have the program set it to true when it's finished doing whatever it's trying to do. Then the code is more self-documenting: WHILE NOT FINISHED keep going through the loop. FINISHED EQUALS TRUE when you're done. Here's an example. This is the code I use to generate a random filename and ensure that there is not already an existing file with the same name. I've added very verbose comments to it to make it clear how it works:

<?php
$finaldir
= 'download';

$finished = false;                       // we're not finished yet (we just started)
while ( ! $finished ):                   // while not finished
 
$rn = rand();                          // random number
 
$outfile = $finaldir.'/'.$rn.'.gif';   // output file name
 
if ( ! file_exists($outfile) ):        // if file DOES NOT exist...
   
$finished = true;                    // ...we are finished
 
endif;
endwhile;                               
// (if not finished, re-start WHILE loop)
?>
up
-30
synnus at gmail dot com
4 years ago
<?php

// test While Vs For php 5.6.17

$t1 = microtime(true);
$a=0;
while(
$a++ <= 1000000000);
$t2 = microtime(true);
$x1 = $t2 - $t1;
echo
PHP_EOL,' > while($a++ <= 100000000); : ' ,$x1, 's', PHP_EOL;

$t3 = microtime(true);
for(
$a=0;$a <= 1000000000;$a++);
$t4 = microtime(true);
$x2 = $t4 - $t3;
echo
PHP_EOL,'> for($a=0;$a <= 100000000;$a++); : ' ,$x2, 's', PHP_EOL;

$t5 = microtime(true);
$a=0; for(;$a++ <= 1000000000;);
$t6 = microtime(true);
$x3 = $t6 - $t5;
echo
PHP_EOL,' > $a=0; for(;$a++ <= 100000000;); : ' , $x3, 's', PHP_EOL;

//> while($a++ <= 100000000);   = 18.509671926498s
//
//> for($a=0;$a <= 100000000;$a++);  =  25.450572013855s
//
//> $a=0; for(;$a++ <= 100000000;);  =  22.614907979965s

// ===================

//> while($a++ != 100000000); : 18.204656839371s
//
//> for($a=0;$a != 100000000;$a++); : 25.025605201721s
//
//> $a=0; for(;$a++ != 100000000;); : 22.340576887131s

// ===================

//> while($a++ < 100000000); : 18.383454084396s
//
//> for($a=0;$a < 100000000;$a++); : 25.290743112564s
//
//> $a=0; for(;$a++ < 100000000;); : 23.28609919548s

?>
up
-32
nickleus at gmail dot com
2 years ago
<?php
$i
= -1;
while (
$i) {
    echo
$i++;
}
?>
outputs  "-1" then stops because "0" (zero) gets evaluated as FALSE.

this demonstrates why it's important for a PDO statement fetch-ing a column value inside a while-loop to test explicitly for FALSE.
up
-35
qeremy [atta] gmail [dotta] com
8 years ago
Instead of this usage;

<?php
$arr
= array("orange", "banana", "apple", "raspberry");

$i = 0;
while (
$i < count($arr)) {
  
$a = $arr[$i];
   echo
$a ."\n";
  
$i++;
}
// or
$i = 0;
$c = count($arr);
while (
$i < $c) {
  
$a = $arr[$i];
   echo
$a ."\n";
  
$i++;
}
?>

This could be more efficient;

<?php
while ($a = $arr[1 * $i++]) echo $a ."\n";
?>
up
-38
er dot sarimkhan786 at gmail dot com
5 years ago
simple pyramid pattern program using while loop
<?php
$i
=1;
while(
$i<=5)
{
   
$j=1;
    while(
$j<=$i)
    {
      echo
"*&nbsp&nbsp";
     
$j++;     
    }
    echo
"<br>";
   
$i++;
}
?>
// or alternatively you can use:
<?php
$i
=1;
while(
$i<=5):

   
$j=1;
    while(
$j<=$i):
      echo
"*&nbsp&nbsp";
     
$j++;     
    endwhile;
   
    echo
"<br>";
   
$i++;
endwhile;
?>
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