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.
while
(PHP 4, PHP 5, PHP 7, PHP 8)
while loops are the simplest type of loop in
PHP. They behave just like their C counterparts. The basic form
of a while statement is:
while (expr)
statement
The meaning of a while statement is simple. It
tells PHP to execute the nested statement(s) repeatedly, as long
as the while expression evaluates to
true. The value of the expression is checked
each time at the beginning of the loop, so even if this value
changes during the execution of the nested statement(s), execution
will not stop until the end of the iteration (each time PHP runs
the statements in the loop is one iteration). If the
while expression evaluates to
false from the very beginning, the nested
statement(s) won't even be run once.
Like with the if statement, you can group
multiple statements within the same while loop
by surrounding a group of statements with curly braces, or by
using the alternate syntax:
while (expr):
statement
...
endwhile;
The following examples are identical, and both print the numbers 1 through 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;
$i++;
endwhile;
?>
add a note
User Contributed Notes 7 notes
scott at mstech dot com ¶
11 years ago
ravenswd at gmail dot com ¶
10 years ago
I find it often clearer to set a simple flag ($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)
?>
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
?>
chayes at antenna dot nl ¶
19 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 ¶
3 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.
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";
?>
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"*  ";
$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;
?>
