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📁 vb实例,很好很好用的哦,处学者的天堂这是第三部分
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<title>第三章：VB语言</title>
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        <td width="100%"><font size="3" color="#8000FF"><strong><em>第三章：VB语言（3）</em></strong></font></td>
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        <td width="100%" style="background-color: rgb(232,255,254)"><p ALIGN="JUSTIFY"><strong><span style="line-height: 25px">五、循环语句</span></strong></p>
        <blockquote>
          <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px">循环结构是计算机语言里一种重要的结构，它的应用广泛，最简单的例子是累加器的作用，还可以用于穷举法，更直观的例子是把某件事重复指定的次数，这样就不用把要重复的语句输入多次，而通过循环结构完成，非常方便。</span></strong></p>
          <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px">C语言里有一个“for”循环语句，VB里也有“For”关键字，作用也差不多，只是VB的“For”语句更容易理解。它的格式是：</span></strong></p>
          <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px"><font color="#004080">For &lt;循环变量&gt;=&lt;初赋值&gt; 
          To &lt;终值&gt; [Step &lt;步长&gt;]</font></span></strong></p>
          <blockquote>
            <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px"><font color="#004080">……<br>
            ……</font></span></strong></p>
          </blockquote>
          <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px"><font color="#004080">Next &lt;循环变量&gt;</font></span></strong></p>
          <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px">在默认情况下，Step被设为“1”，可以省略，Step也可以设为负值，例如：</span></strong></p>
          <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px"><font color="#004080">Dim a=0</font></span></strong></p>
          <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px"><font color="#004080">For I=1 
          To 10 </font></span></strong></p>
          <blockquote>
            <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px"><font color="#004080">a=a+I</font></span></strong></p>
          </blockquote>
          <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px"><font color="#004080">Next I</font></span></strong></p>
          <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px">这是一个最简单的累加器的例子，把1到10累加在一起，然后赋值给“a”这样的效果和上面是一样的，只不过是倒着加罢了，请看：</span></strong></p>
          <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px"><font color="#004080">Dim a=0</font></span></strong></p>
          <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px"><font color="#004080">For I=10 
          To 1 Step –1</font></span></strong></p>
          <blockquote>
            <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px"><font color="#004080">a=a+I</font></span></strong></p>
          </blockquote>
          <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px"><font color="#004080">Next I</font></span></strong></p>
          <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px">While语句也是一个很常用的循环语句，它的形式很多。</span></strong></p>
          <table border="0" cellpadding="0" cellspacing="0" width="100%" msimagelist>
            <tr msimagelist>
              <td valign="top" width="42" msimagelist><img src="bullet4.gif" width="13" height="12" hspace="14"></td>
              <td valign="top" width="100%"><strong><span style="line-height: 25px">Do While …… Loop语句</span></strong></td msimagelist>
            </tr>
            <tr msimagelist>
              <td valign="baseline" width="42" msimagelist><img src="bullet4.gif" width="13" height="12" hspace="14"></td>
              <td valign="top" width="100%"><strong><span style="line-height: 25px">While …… Wend 
              语句</span></strong></td msimagelist>
            </tr>
            <tr msimagelist>
              <td valign="baseline" width="42" msimagelist><img src="bullet4.gif" width="13" height="12" hspace="14"></td>
              <td valign="top" width="100%"><strong><span style="line-height: 25px">Do …… Loop While 
              </span></strong></td msimagelist>
            </tr>
          </table msimagelist>
          <blockquote>
            <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px">While后面都跟逻辑条件判断，“Do 
            While …… Loop语句”和“While …… Wend 语句”作用相似，都是先判断While后面的条件是否为“真”，如果为“真”则执行里面的语句，如果为“假”，则退出循环，循环直至条件为“假”终止。“Do 
            …… Loop While 
            ”与前两者的区别在于，它不管条件的真假，都会先执行“Do”后面的语句，也就是说，它至少执行语句一次。</span></strong></p>
            <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px">与While用法相似的还有Until语句，它是直至条件为真则终止循环，句式把While上述三个语句的While换成Until即可，但是因为容易记混，所以我建议只用While即可。Until 
            &lt;条件&gt;可以相当于While Not &lt;条件&gt;。</span></strong></p>
            <p ALIGN="JUSTIFY"><strong><span style="line-height: 25px">For循环和Whlie循环应当根据适当的环境使用，它们有时也可替换。</span></strong></p>
          </blockquote>
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