PHP - Manual: while

2024-11-15

while

(PHP 4, PHP 5, PHP 7, PHP 8)

while 循环是 PHP 中最简单的循环类型。它和 C 语言中的 while 表现地一样。while 语句的基本格式是：

while (expr)
    statement

while 语句的含意很简单，它告诉 PHP 只要 while 表达式的值为 true 就重复执行嵌套中的循环语句。表达式的值在每次开始循环时检查，所以即使这个值在循环语句中改变了，语句也不会停止执行，直到本次循环结束。如果 while 表达式的值一开始就是 false，则循环语句一次都不会执行。

和 if 语句一样，可以在 while 循环中用花括号括起一个语句组，或者用替代语法：

while (expr):
    statement
    ...
endwhile;

下面两个例子完全一样，都显示数字 1 到 10：


<?php
/* 示例 1 */

$i = 1;
while ($i <= 10) {
    echo $i++;  /* 在自增前（后自增）打印的值将会是 $i */
}

/* 示例 2 */

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

add a note

User Contributed Notes 9 notes

down

Dan Liebner ¶

1 year ago


While loops don't require a code block (statement).

<?php

while( ++$i < 10 ); // look ma, no brackets!

echo $i; // 10

?>

down

-27

mparsa1372 at gmail dot com ¶

1 year 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;
}
?>

down

-47

nickleus at gmail dot com ¶

4 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.

down

-52

er dot sarimkhan786 at gmail dot com ¶

6 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;
?>

down

-59

scott at mstech dot com ¶

12 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.

down

-52

ravenswd at gmail dot com ¶

12 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)
?>

down

-61

chayes at antenna dot nl ¶

20 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;

?>

down

-59

synnus at gmail dot com ¶

6 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

?>

down

-62

qeremy [atta] gmail [dotta] com ¶

9 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";
?>

add a note

官方地址：https://www.php.net/manual/en/control-structures.while.php

有任何技术问题请点击这里网站运营推广招聘

IT PHP 编程语言 Linux 开发编程科技 Elasticsearch HTML/CSS/XML 网络 JAVA NoSQL 数据库面试 C/C++ Golang Git 算法操作系统正则表达式 Redis 互联网 MySql JavaScript 运维软件国际架构设计 Mac OS TCP/IP Excel Vim Windows Socket Oracle VR MongoDB Python 运营 MemCache 商业硬件电子娱乐设计 nginx 摄影游戏 WordPress HTTP 团建数码电器

php7 安装fileinfo扩展 preg_split — 通过一个正则表达式分隔字符串 php位值,解决 PHP 中 usort 在值相同时改变原始位置的问题 [PHP] inet_pton/inet_ntop IP地址转换函数 array_multisort() 多字段排序 PHPMailer设置utf8 PHPMailer字符集CharSet ADORecordSet对象 adodb手册 PHP 8.1 [鸟哥]PHP_INT_MIN 和 -9223372036854775808 opcache预加载 Composer的Packagist资源 mysql面试题 [鸟哥]PHP FFI详解 - 一种全新的PHP扩展方式 PHP7添加redis扩展 PHP获取指定函数定义在哪个文件中及行号 PHP mkdir()写出来的权限与mode值不符合 Packagist / Composer 中国全量镜像 adodb连接mysql多个数据库的问题常用的php ADODB使用方法集锦

略微加速

PHP官方手册 - 互联网笔记

while

User Contributed Notes 9 notes