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          <title>javascrip教程</title>
          <strong><font face="宋体" size="3">第七页：if-then语句的例子</font></strong> 
          <p><font face="宋体" size="3">如果你在即时对话框中键入<tt>yes</tt>，你将在看到本页其他部分前收<br>
            到一个亲切的问候。若敲入别的则没有。</font></p>
          <p><font face="宋体" size="3">这里是该语句的核心：</font></p>
          <font color="#000000"> 
          <p>var monkey_love = prompt(&quot;你喜欢网猴吗？&quot;,&quot;敲入是<br>
            或否。&quot;);</p>
          </font> 
          <p><font face="宋体" size="3">if (monkey_love == &quot;是&quot;)<br>
            <br>
            {<br>
            <br>
            </font><font color="#000000">alert(&quot;谢谢！很高兴您能来这儿！请往下读吧！&quot;);</font></p>
          <p><font face="宋体" size="3"><br>
            }<br>
            <br>
            第一行你见过。它唤起一个对话框并将用户的反馈调入变<br>
            量<tt>monkey_love</tt>中。但第二行就有些不同：它有个条件，即如果<br>
            变量<tt>monkey_love</tt>等于值&quot;是&quot; ，则运行花括号中的语句。若它<br>
            等于其他值，则不运行。</font></p>
          <p><font face="宋体"><font size="3">注意该条件中的两个等于标记，这是人们容易搞混的地方之<br>
            一。如果你只用一个标记，实际上是告诉JavaScript测试是<br>
            否<tt>monkey_love</tt></font><tt><font size="4">等于</font></tt><font size="3"> 
            &quot;是&quot;。幸运的是，多数浏览器在你运行这<br>
            些语句时会识别这些错误并警告你。但最好现在开始就注意别<br>
            犯这种错误。</font></font></p>
          <p><font face="宋体" size="3">其他重要的条件是：</font></p>
          <p><font face="宋体" size="3">(variable_1 &gt; variable_2)&nbsp; is true 
            if variable_1 is greater than variable_2<br>
            <br>
            (variable_1 &lt; variable_2)&nbsp; is true if variable_1 is less than 
            variable_2<br>
            <br>
            (variable_2 &lt;= variable_2)&nbsp; is true if variable_1 is less 
            than or equal to variable_2<br>
            <br>
            (variable_1 != variable_2)&nbsp; is true if variable_1 does <b>not</b> 
            equal variable_2<br>
            <br>
            有两个方法可使你的条件更合理：</font></p>
          <p><font face="宋体" size="3">在运行花括号中的语句前如果你想要两件事为“是”，可这<br>
            样做：</font></p>
          <p><font face="宋体" size="3"><br>
            if ((variable_1 &gt; 18) &amp;&amp; (variable_1 &lt; 21)) <br>
            <br>
            { <br>
            <br>
            &nbsp; document.writeln(&quot;variable_1 can vote, but can't drink.&quot;);<br>
            <br>
            }<br>
            <br>
            </font></p>
          <p><font face="宋体" size="3">注意这里的两个“&amp;&amp;”在JavaScript中这是“与”的意思。也<br>
            注意整个子句有两个部分，&amp;&amp;须在圆括号中。</font></p>
          <p><font face="宋体" size="3">若想两件事之一为真，这样做：</font></p>
          <p><font face="宋体" size="3"><br>
            if ((variable_1 == &quot;bananas&quot;) || (variable_1 == &quot;JavaScript&quot;)) 
            <br>
            <br>
            { <br>
            <br>
            &nbsp; document.writeln(&quot;The monkey is happy because it has &quot; 
            + &nbsp; variable_1);<br>
            <br>
            }<br>
            <br>
            </font></p>
          <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 face="宋体" size="3"><font color="#FF0000">第一页</font>：<a href="day2_1.html">第二天课程简介</a><br>
            <font color="#FF0000">第二页</font>：<a href="day2_2.html">变量介绍</a><br>
            <font color="#FF0000">第三页</font>：<a href="day2_3.html">首个变量例子的程序主体</a><br>
            <font color="#FF0000">第四页</font>：<a href="day2_4.html">字符串的魔力<br>
            </a><font color="#FF0000">第五页</font>：<a href="day2_5.html">变量练习</a><a href="day2_4.html"> 
            </a></font><font face="宋体" size="3"><br>
            <font color="#FF0000">第</font><font face="宋体" size="3"><font color="#FF0000">六</font></font><font color="#FF0000">页</font>：<a href="day2_6.html">if-then子句</a><br>
            <font color="#FF0000">第</font><font face="宋体" size="3"><font color="#FF0000">七</font></font><font color="#FF0000">页</font>：if-then语句的例子 
            <br>
            <font color="#FF0000">第八页</font>：<a href="day2_9.html">链结事件</a><br>
            <font color="#FF0000">第</font><font face="宋体" size="3"><font color="#FF0000">九</font></font><font color="#FF0000">页</font>：<a href="day2_10.html">图片交换</a><br>
            <font color="#FF0000">第十页</font>：<a href="day2_12.html">复习</a><br>
            </font></p>
          <p align="left"><font face="宋体" size="3">[<a href="index.html">第1课</a>][第2课][<a href="day3_1.html">第3课</a>][<a href="day4_1.html">第4课</a>][<a href="day5_1.html">第5课</a>]</font></p>
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