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)
Los bucles while son el tipo más sencillo de bucle en
PHP. Se comportan igual que su contrapartida en C. La forma básica
de una sentencia while es:
while (expr)
sentencia
El significado de una sentencia while es simple. Le
dice a PHP que ejecute las sentencias anidadas, tanto
como la expresión while se evalúe como
true. El valor de la expresión es verificado
cada vez al inicio del bucle, por lo que incluso si este valor
cambia durante la ejecución de las sentencias anidadas, la ejecución
no se detendrá hasta el final de la iteración (cada vez que PHP ejecuta
las sentencias contenidas en el bucle es una iteración). A veces, si la
expresión while se evalúa como
false desde el principio, las sentencias
anidadas no se ejecutarán ni siquiera una vez.
Al igual que con la sentencia if, se pueden agrupar
varias instrucciones dentro del mismo bucle while
rodeando un grupo de sentencias con corchetes, o
utilizando la sintaxis alternativa:
while (expr):
sentencias
...
endwhile;
Los siguientes ejemplos son idénticos y ambos presentan los números del 1 al 10:
<?php
/* ejemplo 1 */
$i = 1;
while ($i <= 10) {
echo $i++; /* el valor presentado sería
$i antes del incremento
(post-incremento) */
}
/* ejemplo 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;
?>
