control-structures.do.while.html
来自「php的帮助文档,涉及到PHP的案例和基本语法,以及实际应用内容」· HTML 代码 · 共 73 行
HTML
73 行
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>do-while</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="control-structures.while.html">while</a></div> <div class="next" style="text-align: right; float: right;"><a href="control-structures.for.html">for</a></div> <div class="up"><a href="language.control-structures.html">Control Structures</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="control-structures.do.while" class="sect1"> <h2 class="title"><i>do-while</i></h2> <p class="simpara"> <i>do-while</i> loops are very similar to <i>while</i> loops, except the truth expression is checked at the end of each iteration instead of in the beginning. The main difference from regular <i>while</i> loops is that the first iteration of a <i>do-while</i> loop is guaranteed to run (the truth expression is only checked at the end of the iteration), whereas it may not necessarily run with a regular <i>while</i> loop (the truth expression is checked at the beginning of each iteration, if it evaluates to <b><tt>FALSE</tt></b> right from the beginning, the loop execution would end immediately). </p> <p class="para"> There is just one syntax for <i>do-while</i> loops: <div class="informalexample"> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br />$i </span><span style="color: #007700">= </span><span style="color: #0000BB">0</span><span style="color: #007700">;<br />do {<br /> echo </span><span style="color: #0000BB">$i</span><span style="color: #007700">;<br />} while (</span><span style="color: #0000BB">$i </span><span style="color: #007700">> </span><span style="color: #0000BB">0</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> <p class="simpara"> The above loop would run one time exactly, since after the first iteration, when truth expression is checked, it evaluates to <b><tt>FALSE</tt></b> ($i is not bigger than 0) and the loop execution ends. </p> <p class="para"> Advanced C users may be familiar with a different usage of the <i>do-while</i> loop, to allow stopping execution in the middle of code blocks, by encapsulating them with <i>do-while</i> (0), and using the <a href="control-structures.break.html" class="link"><i>break</i></a> statement. The following code fragment demonstrates this: <div class="informalexample"> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #007700">do {<br /> if (</span><span style="color: #0000BB">$i </span><span style="color: #007700">< </span><span style="color: #0000BB">5</span><span style="color: #007700">) {<br /> echo </span><span style="color: #DD0000">"i is not big enough"</span><span style="color: #007700">;<br /> break;<br /> }<br /> </span><span style="color: #0000BB">$i </span><span style="color: #007700">*= </span><span style="color: #0000BB">$factor</span><span style="color: #007700">;<br /> if (</span><span style="color: #0000BB">$i </span><span style="color: #007700">< </span><span style="color: #0000BB">$minimum_limit</span><span style="color: #007700">) {<br /> break;<br /> }<br /> echo </span><span style="color: #DD0000">"i is ok"</span><span style="color: #007700">;<br /><br /> </span><span style="color: #FF8000">/* process i */<br /><br /></span><span style="color: #007700">} while (</span><span style="color: #0000BB">0</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> <p class="simpara"> Don't worry if you don't understand this right away or at all. You can code scripts and even powerful scripts without using this 'feature'. </p> </div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="control-structures.while.html">while</a></div> <div class="next" style="text-align: right; float: right;"><a href="control-structures.for.html">for</a></div> <div class="up"><a href="language.control-structures.html">Control Structures</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div></body></html>⌨️ 快捷键说明
复制代码Ctrl + C
搜索代码Ctrl + F
全屏模式F11
增大字号Ctrl + =
减小字号Ctrl + -
显示快捷键?