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<title>Webmonkey: javascript: Thau's JavaScript Tutorial: Day 1</title>
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<td WIDTH="68%" VALIGN="MIDDLE"><font FACE="宋体" LANG="ZH-CN" SIZE="4" COLOR="#ff0000"><!--Figure out which page title to display --></font><b><font
FACE="System,黑体" LANG="ZH-CN" COLOR="#ff0000">第</font><font FACE="宋体"
LANG="ZH-CN" COLOR="#ff0000">6</font><font FACE="System,黑体" LANG="ZH-CN"
COLOR="#ff0000">页</font><font FACE="宋体" LANG="ZH-CN" COLOR="#ff0000">: if-then </font><font
FACE="System,黑体" LANG="ZH-CN" COLOR="#ff0000">子句</font></b><font
FACE="System,黑体" LANG="ZH-CN"><br>
<!-- BYLINE --> </font><font FACE="System,黑体" LANG="ZH-CN" SIZE="2">作者：</font><a
HREF="mailto:thau@wired.com"><font FACE="宋体" LANG="ZH-CN" SIZE="2">Thau!</font></a><font
FACE="宋体" LANG="ZH-CN"> <!-- SEE ALSO LINKS --></font></td>
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<td WIDTH="68%" VALIGN="TOP" BGCOLOR="#ffffff"><font FACE="宋体" LANG="ZH-CN" SIZE="2">"if-then"
</font><font FACE="System,黑体" LANG="ZH-CN" SIZE="2">子句的应用可以使得程序根据用户输入的值作出不同的反应。例如你可以写一段程序使得它对你与对其他人反应不同。这里是它的基本格式：</font><pre>
if (some condition is true)
{
do something;
do something;
do something;
}
</pre>
<font FACE="System,黑体" LANG="ZH-CN" SIZE="2"><p>本结构的重要部分</font><font
FACE="宋体" LANG="ZH-CN" SIZE="2">:<ul>
</font><font FACE="System,黑体" LANG="ZH-CN" SIZE="2">
<li>以单词</font><font FACE="宋体" LANG="ZH-CN" SIZE="2"> "</font><tt>if</tt><font
FACE="宋体" LANG="ZH-CN" SIZE="2">"</font><font FACE="System,黑体" LANG="ZH-CN"
SIZE="2">开始</font><font FACE="宋体" LANG="ZH-CN" SIZE="2"> (</font><tt>if</tt><font
FACE="宋体" LANG="ZH-CN" SIZE="2"> </font><font FACE="System,黑体" LANG="ZH-CN"
SIZE="2">必须小写</font><font FACE="宋体" LANG="ZH-CN" SIZE="2">). </li>
</font><font FACE="System,黑体" LANG="ZH-CN" SIZE="2">
<li>圆括弧中是条件：非真即伪。</font> </li>
<font FACE="System,黑体" LANG="ZH-CN" SIZE="2">
<li>如果条件为真的话执行花括弧中的语句。</font> </li>
</ul>
<font FACE="System,黑体" LANG="ZH-CN" SIZE="2"><p>记住：空格是唯一保持程序可读性的东西。当然你可以将整个</font><font
FACE="宋体" LANG="ZH-CN" SIZE="2">if-then</font><font FACE="System,黑体" LANG="ZH-CN"
SIZE="2">语句写在一行中，但它读起来就费劲了。</p>
<p>这里是一个</font><a HREF="tppmsgs/msgs0.htm#63"><font FACE="宋体" LANG="ZH-CN"
SIZE="2"> if-then </font><font FACE="System,黑体" LANG="ZH-CN" SIZE="2">子句的例子</font></a></p>
<font FACE="System,黑体" LANG="ZH-CN"><p>第</font><font FACE="宋体" LANG="ZH-CN">1</font><font
FACE="System,黑体" LANG="ZH-CN">页：<a HREF="tutorial2.html">第二天课程简介</a><br>
第</font><font FACE="宋体" LANG="ZH-CN">2</font><font FACE="System,黑体" LANG="ZH-CN">页</font><font
FACE="宋体" LANG="ZH-CN">: </font><font FACE="System,黑体" LANG="ZH-CN"><a
HREF="tutorial2_page2.html">变量介绍</a><br>
第</font><font FACE="宋体" LANG="ZH-CN">3</font><font FACE="System,黑体" LANG="ZH-CN">页</font><font
FACE="宋体" LANG="ZH-CN">:</font><font FACE="System,黑体" LANG="ZH-CN"><a
HREF="tutorial2_page3.html">首个变量例子的程序主体</a><br>
第</font><font FACE="宋体" LANG="ZH-CN">4</font><font FACE="System,黑体" LANG="ZH-CN">页</font><font
FACE="宋体" LANG="ZH-CN">: </font><font FACE="System,黑体" LANG="ZH-CN"><a
HREF="tutorial2_page4.html">字符串的魔力</a><br>
第</font><font FACE="宋体" LANG="ZH-CN">5</font><font FACE="System,黑体" LANG="ZH-CN">页</font><font
FACE="宋体" LANG="ZH-CN">: </font><font FACE="System,黑体" LANG="ZH-CN"><a
HREF="tutorial2_page5.html">变量练习</a><br>
第</font><font FACE="宋体" LANG="ZH-CN">6</font><font FACE="System,黑体" LANG="ZH-CN">页</font><font
FACE="宋体" LANG="ZH-CN">: <a HREF="tutorial2_page6.html">if-then </font><font
FACE="System,黑体" LANG="ZH-CN">子句</a><br>
第</font><font FACE="宋体" LANG="ZH-CN">7</font><font FACE="System,黑体" LANG="ZH-CN">页</font><font
FACE="宋体" LANG="ZH-CN">: <a HREF="tutorial2_page7.html">if-then </font><font
FACE="System,黑体" LANG="ZH-CN">语句的例子</a><br>
第</font><font FACE="宋体" LANG="ZH-CN">8</font><font FACE="System,黑体" LANG="ZH-CN">页</font><font
FACE="宋体" LANG="ZH-CN">: <a HREF="tutorial2_page8.html">if-then </font><font
FACE="System,黑体" LANG="ZH-CN">练习</a><br>
第</font><font FACE="宋体" LANG="ZH-CN">9</font><font FACE="System,黑体" LANG="ZH-CN">页</font><font
FACE="宋体" LANG="ZH-CN">: </font><font FACE="System,黑体" LANG="ZH-CN"><a
HREF="tutorial2_page9.html">链结事件</a><br>
第</font><font FACE="宋体" LANG="ZH-CN">10</font><font FACE="System,黑体"
LANG="ZH-CN">页</font><font FACE="宋体" LANG="ZH-CN">: </font><font
FACE="System,黑体" LANG="ZH-CN"><a HREF="tutorial2_page10.html">图片交换</a><br>
第</font><font FACE="宋体" LANG="ZH-CN">11</font><font FACE="System,黑体"
LANG="ZH-CN">页</font><font FACE="宋体" LANG="ZH-CN">: </font><a
HREF="tutorial2_page11.html"><font FACE="System,黑体" LANG="ZH-CN">练习</font><font
FACE="宋体" LANG="ZH-CN"> 2</a><br>
</font><font FACE="System,黑体" LANG="ZH-CN">第</font><font FACE="宋体" LANG="ZH-CN">12</font><font
FACE="System,黑体" LANG="ZH-CN">页</font><font FACE="宋体" LANG="ZH-CN">: </font><font
FACE="System,黑体" LANG="ZH-CN"><a HREF="tutorial2_page12.html">复习</a></font></td>
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