<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >while</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REL="HOME" TITLE="PHP 手册" HREF="index.html"><LINK REL="UP" TITLE="控制结构" HREF="language.control-structures.html"><LINK REL="PREVIOUS" TITLE="流程控制的替代语法" HREF="control-structures.alternative-syntax.html"><LINK REL="NEXT" TITLE="do-while" HREF="control-structures.do.while.html"><META HTTP-EQUIV="Content-type" CONTENT="text/html; charset=UTF-8"></HEAD ><BODY CLASS="sect1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >PHP 手册</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="control-structures.alternative-syntax.html" ACCESSKEY="P" >上一页</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >章 16. 控制结构</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="control-structures.do.while.html" ACCESSKEY="N" >下一页</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="sect1" ><H1 CLASS="sect1" ><A NAME="control-structures.while" ><TT CLASS="literal" >while</TT ></A ></H1 ><P > <TT CLASS="literal" >while</TT > 循环是 PHP 中最简单的循环类型。它和 C 语言中的 <TT CLASS="literal" >while</TT > 表现得一样。<TT CLASS="literal" >while</TT > 语句的基本格式是: <DIV CLASS="informalexample" ><P ></P ><A NAME="AEN4759" ></A ><TABLE BORDER="0" BGCOLOR="#E0E0E0" CELLPADDING="5" ><TR ><TD ><PRE CLASS="programlisting" >while (expr) statement</PRE ></TD ></TR ></TABLE ><P ></P ></DIV > </P ><P > <TT CLASS="literal" >while</TT > 语句的含意很简单,它告诉 PHP 只要 <TT CLASS="literal" >while</TT > 表达式的值为 <TT CLASS="constant" ><B >TRUE</B ></TT > 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。有时候如果 <TT CLASS="literal" >while</TT > 表达式的值一开始就是 <TT CLASS="constant" ><B >FALSE</B ></TT >,则循环语句一次都不会执行。 </P ><P > 和 <TT CLASS="literal" >if</TT > 语句一样,可以在 <TT CLASS="literal" >while</TT > 循环中用花括号括起一个语句组,或者用替代语法: <DIV CLASS="informalexample" ><P ></P ><A NAME="AEN4770" ></A ><TABLE BORDER="0" BGCOLOR="#E0E0E0" CELLPADDING="5" ><TR ><TD ><PRE CLASS="programlisting" >while (expr): statement ... endwhile;</PRE ></TD ></TR ></TABLE ><P ></P ></DIV > </P ><P > 下面两个例子完全一样,都显示数字 1 到 10: <DIV CLASS="informalexample" ><P ></P ><A NAME="AEN4773" ></A ><TABLE BORDER="0" BGCOLOR="#E0E0E0" CELLPADDING="5" ><TR ><TD ><code><font color="#000000"> <font color="#0000BB"><?php<br /></font><font color="#FF8000">/* example 1 */<br /><br /></font><font color="#0000BB">$i </font><font color="#007700">= </font><font color="#0000BB">1</font><font color="#007700">;<br />while (</font><font color="#0000BB">$i </font><font color="#007700"><= </font><font color="#0000BB">10</font><font color="#007700">) {<br /> echo </font><font color="#0000BB">$i</font><font color="#007700">++; </font><font color="#FF8000">/* the printed value would be<br /> $i before the increment<br /> (post-increment) */<br /></font><font color="#007700">}<br /><br /></font><font color="#FF8000">/* example 2 */<br /><br /></font><font color="#0000BB">$i </font><font color="#007700">= </font><font color="#0000BB">1</font><font color="#007700">;<br />while (</font><font color="#0000BB">$i </font><font color="#007700"><= </font><font color="#0000BB">10</font><font color="#007700">):<br /> print </font><font color="#0000BB">$i</font><font color="#007700">;<br /> </font><font color="#0000BB">$i</font><font color="#007700">++;<br />endwhile;<br /></font><font color="#0000BB">?></font> </font> </code></TD ></TR ></TABLE ><P ></P ></DIV > </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="control-structures.alternative-syntax.html" ACCESSKEY="P" >上一页</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >起始页</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="control-structures.do.while.html" ACCESSKEY="N" >下一页</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >流程控制的替代语法</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="language.control-structures.html" ACCESSKEY="U" >上一级</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><TT CLASS="literal" >do-while</TT ></TD ></TR ></TABLE ></DIV ></BODY ></HTML >