While loops don't require a code block (statement).
<?php
while( ++$i < 10 ); // look ma, no brackets!
echo $i; // 10
?>
while
(PHP 4, PHP 5, PHP 7, PHP 8)
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;
?>
add a note
User Contributed Notes 9 notes
Dan Liebner ¶
3 years ago
mparsa1372 at gmail dot com ¶
3 years ago
The example below displays the numbers from 1 to 5:
<?php
$x = 1;
while($x <= 5) {
echo "The number is: $x <br>";
$x++;
}
?>
This example counts to 100 by tens:
<?php
$x = 0;
while($x <= 100) {
echo "The number is: $x <br>";
$x+=10;
}
?>
scott at mstech dot com ¶
14 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.
synnus at gmail dot com ¶
8 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
?>
ravenswd at gmail dot com ¶
14 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)
?>
qeremy [atta] gmail [dotta] com ¶
11 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 $a ."\n";
?>
chayes at antenna dot nl ¶
22 years ago
At the end of the while (list / each) loop the array pointer will be at the end.
This means the second while loop on that array will be skipped!
You can put the array pointer back with the reset($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;
?>
nickleus at gmail dot com ¶
6 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.
er dot sarimkhan786 at gmail dot com ¶
8 years ago
simple pyramid pattern program using while loop
<?php
$i=1;
while($i<=5)
{
$j=1;
while($j<=$i)
{
echo"*  ";
$j++;
}
echo"<br>";
$i++;
}
?>
// or alternatively you can use:
<?php
$i=1;
while($i<=5):
$j=1;
while($j<=$i):
echo"*  ";
$j++;
endwhile;
echo"<br>";
$i++;
endwhile;
?>
