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<title>第三章：VB语言</title>
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<div align="center"><center><table border="0" cellpadding="8" cellspacing="0" width="100%">
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<td width="100%"><font size="3" color="#8000FF"><strong><em>第三章：VB语言（1）</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: 24px"><font color="#004080">本章提要：</font></span></strong></p>
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<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: 24px"><font color="#000080">VB语法与Basic的异同</font></span></strong></td msimagelist>
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<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: 24px"><font color="#000080">注释语句</font></span></strong></td msimagelist>
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<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: 24px"><font color="#000080">长语句的分行</font></span></strong></td msimagelist>
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<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: 24px"><font color="#000080">条件语句</font></span></strong></td msimagelist>
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<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: 24px"><font color="#000080">循环语句</font></span></strong></td msimagelist>
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<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: 24px"><font color="#000080">运算操作</font></span></strong></td msimagelist>
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<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: 24px"><font color="#000080">数据定义与赋值</font></span></strong></td msimagelist>
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<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: 24px"><font color="#000080">函数和过程</font></span></strong></td msimagelist>
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<p><strong><span style="line-height: 24px">一、VB与Basic</span></strong></p>
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<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: 24px">VB之所以叫做“Visual
Basic”就是因为它使用了Basic语言作为代码，所以它们之间有着千丝万缕的关系，如果学过Basic的话，看到VB的程序结构会感到很亲切。但VB作为新生物，也超越了Basic的限制，有了许多自己的特点：</span></strong></td msimagelist>
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<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: 24px">VB建立了一种新的变量类型――货币型变量，通过使用仅带有二位小数的货币变量，就能避免因使用实型变量而带来的数值积累误差问题。</span></strong></td msimagelist>
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<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: 24px">VB在调用函数（Function）时，必须在函数名后跟一对括号。</span></strong></td msimagelist>
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<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: 24px">VB对白兰地使用范围重新做了规范，在Basic里把隐含变量都当作全局变量，而在VB里对隐含变量都当作局部变量。</span></strong></td msimagelist>
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<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: 24px">VB里的说明语句（Declare），仅支持动态链结库（DLL）的子程序和无变量函数。</span></strong></td msimagelist>
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<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: 24px">使用数组，必须事先用Dim或Redim进行定义。</span></strong></td msimagelist>
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<p><strong><span style="line-height: 24px">二、注释语句 </span></strong><ol>
<p ALIGN="JUSTIFY"><strong><span style="line-height: 24px">在使用注释语句之前必须先了解注释的作用，注释不仅仅是对程序的解释，有时它对于程序的调试也非常有用，譬如说可以利用注释屏蔽一条语句以观察变化，发现问题和错误。以后注释语句将是我们在编程里最经常用到的语句之一。</span></strong></p>
<p ALIGN="JUSTIFY"><strong><span style="line-height: 24px">在VB里，注释语句有两种，一种是用“Rem”关键字，这跟DOS里的批处理文件的用法一样，还有一种是利用单引号“’”，例如：</span></strong></p>
<p ALIGN="JUSTIFY"><strong><span style="line-height: 24px"><font color="#008000">‘Dim a
As String </font>与</span></strong></p>
<p ALIGN="JUSTIFY"><strong><span style="line-height: 24px"><font color="#008000">Rem Dim a
As String </font>的作用是一致的。</span></strong></p>
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<p><strong><span style="line-height: 24px">三、长语句的分行</span></strong><ol>
<p ALIGN="JUSTIFY"><strong><span style="line-height: 24px">在比较早的版本中，因为没有象C等语言用“；”隔开语句与语句，VB的语句是必须写在一行里的，不过后来版本的VB里如许用分行符“_”把一个长语句分成若干行来存放。</span></strong></p>
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