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<td bgcolor="#ffff99" width="451">JavaScript教程 - 第四课</td>
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<td bgcolor="#FF6600" width="451"><a href="mailto:thau@wired.com">Thau</a></td>
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<td width="458" valign="top" align="left"><strong><small><small><br>
</small></small><font face="宋体" size="3">第二页：</font><font SIZE="3">循环介绍</font></strong>
<p><font SIZE="3">有时你想反复做同一件事。你想向某些人询问一个口令，你不<br>
断地问，直到得到正确的口令。如果你只想给他们两次尝试的<br>
机会，你可以这么做：</font> <ul>
<pre><font SIZE="3">
<font face="verdana, arial, geneva, sans-serif">var the_password = "pass the wrench";
var answer = prompt("What's the woyd?","");
if (answer != the_password) {
answer = prompt("What's the woyd?","");
if (password != the_password) {
document.write("You lose!<p>");
} else {
document.write("That's right!<p>");
}
} else {
document.write("That's right!<p>");
}
</font></font></pre>
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<p ALIGN="JUSTIFY"><font SIZE="3">不幸的是如果你想不住地问直到得到正确答案，上述做法是不<br>
起作用的。假使你是想询问四次而不是两次，那这已经是很讨<br>
厌的事了。你将使用四个层次的</font><font size="2"
face="verdana, arial, geneva, sans-serif">if-then </font><font SIZE="3">子句，这决不是件好事。</font></p>
<font SIZE="3"><p ALIGN="JUSTIFY">反复做相似的事情的最好方法是使用一个循环<font
face="verdana, arial, geneva, sans-serif"><font FACE="Times New Roman">(loop</font>)</font>。在这种<br>
情况下，你可以用一个循环来不断的要求口令直到这个人说出<br>
为止。这里有一个<a href="day4_3.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_3.html"><font
face="verdana, arial, geneva, sans-serif">while</font>循环工作的例子</a>，口令是：<font
face="verdana, arial, geneva, sans-serif"><b>pass the<br>
wrench</b></font>。</p>
</font><p align="left"><font face="宋体" size="3" color="#000000"><strong>JavaScript教程</strong></font><font
color="#FF0000" face="宋体" size="3"><br>
</font><font size="3" color="#FF0000">第一页</font><font size="2" face="宋体"> </font><a
href="day4_2.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_2.html"><font SIZE="3">第四课介绍</font></a><font size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第二页</font> 循环介绍</font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第三页</font> <a href="day4_3.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_3.html">循环的密码</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第四页</font> <a href="day4_4.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_4.html">再谈<font
face="宋体">WHILE</font>循环</a></font><font size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第五页</font> <a href="day4_5.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_5.html">For循环</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第六页</font> <a href="day4_6.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_6.html">嵌套循环</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第七页</font> <a href="day4_7.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_7.html">循环练习</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第八页</font> <a href="day4_8.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_8.html">数组</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第九页</font> <a href="day4_9.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_9.html">数组和循环</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第十页</font> <a href="day4_10.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_10.html">文件目标模块中的数组</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第十一页</font> <a href="day4_11.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_11.html">函数</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第十二页</font> <a href="day4_12.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_12.html">无参数函数</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第十三页</font> <a href="day4_13.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_13.html">参数及返回值</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第十四页</font> <a href="day4_14.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_14.html">多于一个参数的函数</a></font></p>
<p align="left"><font face="宋体" size="3">[<a href="index.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/index.html">第1课</a>][<a
href="day2_1.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day2_1.html">第2课</a>][<a href="day3_1.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day3_1.html">第3课</a>][第4课][<a
href="day5_1.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day5_1.html">第5课</a>]</font></p>
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