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1.0pt'> </span></b><span lang=EN-US style='letter-spacing:
1.0pt'> If语句的嵌套是指if 或else后面的语句块中又包含If语句。语句形式：</span><span lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><span lang=EN-US style='letter-spacing:1.0pt'>
<b><span style='color:blue'> If <</span><span style='color:maroon'>表达式1</span><span
style='color:blue'>> Then<br>
If <</span><span style='color:maroon'>表达式11</span><span
style='color:blue'>> Then</span></b></span><span lang=EN-US> <br>
<b><span style='color:red'> </span></b> <b><span style='color:red;
letter-spacing:1.0pt'>……</span></b> <br>
<b><span style='color:blue'> </span></b> <b><span style='color:blue;
letter-spacing:1.0pt'>End If</span></b> <br>
<b> </b> <b><span style='color:blue;letter-spacing:1.0pt'>……</span></b> <br>
<b><span style='color:blue'> </span></b> <b><span style='color:blue;
letter-spacing:1.0pt'>End If</span></b> <o:p></o:p></span></p>
<p style='layout-grid-mode:char'><b><span style='letter-spacing:1.0pt'> 注意：</span></b><span
lang=EN-US style='letter-spacing:1.0pt'> <br>
1）对于嵌套结构，为了增强程序的可读性，应该采用缩进形式书写；<br>
2）If语句形式若不在一行上书写，必须与End If配对，多个if嵌套，End If与它最接近的Emd If配对。</span><span
lang=EN-US><br clear=all>
<b> <span style='letter-spacing:1.0pt'>例</span></b><span style='letter-spacing:
1.0pt'>： 已知x、y、z三个数，比较它们的大小并排序，使得x>y>z.</span><o:p></o:p></span></p>
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<p style='margin-left:11.25pt;text-indent:-11.25pt;tab-stops:list 11.25pt;
layout-grid-mode:char'><b><span lang=EN-US style='letter-spacing:1.0pt'>2.</span></b><b><span
lang=EN-US style='font-size:7.0pt;font-family:"Times New Roman";letter-spacing:
1.0pt'> </span><span lang=EN-US style='letter-spacing:1.0pt'>Select Case语句（情况语句）</span></b>
<span style='letter-spacing:1.0pt'> 是多分支语句的又一种形式，语句形式：</span> <span
lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><b><span style='color:blue;letter-spacing:
1.0pt'> <span lang=EN-US>Select Case </span></span><span lang=EN-US
style='letter-spacing:1.0pt'> <span style='color:red'>变量或表达式<br>
</span><span style='color:blue'> </span><span style='color:red'> </span><span
style='color:blue'>Case</span> <span style='color:teal'>表达式列表1</span></span></b><span
lang=EN-US> <br>
<b> </b> <b> <span style='color:purple;letter-spacing:1.0pt'>语句块1</span></b><br>
<b><span style='color:blue'> </span></b> <b><span style='color:blue;
letter-spacing:1.0pt'> Case</span><span style='letter-spacing:1.0pt'> <span
style='color:teal'>表达式列表2</span> <br>
</span> <span style='color:purple;letter-spacing:1.0pt'>语句块2</span></b>
<br>
<b> </b> <b> <span style='letter-spacing:1.0pt'>…… <br>
[<span style='color:blue'>Case Else</span> </span></b><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><b><span lang=EN-US style='letter-spacing:
1.0pt'> <span style='color:purple'> 语句块n+1</span>]<br>
<span style='color:blue'> </span> <span style='color:blue'>End Select</span></span></b><span
lang=EN-US><o:p></o:p></span></p>
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<p style='layout-grid-mode:char'><b> <span style='letter-spacing:1.0pt'>说明：</span></b><span
lang=EN-US style='letter-spacing:1.0pt'>1）<span style='color:blue'>变量或表达式</span>可以是数值型或字符串表达式</span><span
lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><span lang=EN-US style='letter-spacing:1.0pt'>
2）<span style='color:blue'>表达式列表I</span> 可以是表达式、一组用逗号分隔的枚举值、表达式1 to 表达式2、Is关系运算符表达式；如：<b>case
1 to 10 、 case
"a","w","e","t" 、 case
2,4,6,8,is>10</b></span><span lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><span lang=EN-US style='letter-spacing:1.0pt'>
3）并不是所有的多分支结构都可以用情况语句代替的。</span><span lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><b> <span style='letter-spacing:1.0pt'>例</span></b><span
style='letter-spacing:1.0pt'>：已知输入某课程的百分制成绩<span lang=EN-US>mark，要求显示对应五级制的评定，评定条件如下：</span></span><span
lang=EN-US><o:p></o:p></span></p>
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mso-cellspacing:0cm;mso-padding-alt:0cm 0cm 0cm 0cm' height=90>
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<td width=116 style='width:87.0pt;padding:0cm 0cm 0cm 0cm;height:36.0pt'>
<p class=MsoNormal><span style='font-size:10.0pt;color:#333399'>优<span
lang=EN-US><o:p></o:p></span></span></p>
</td>
<td width=123 style='width:92.25pt;padding:0cm 0cm 0cm 0cm;height:36.0pt'>
<p class=MsoNormal><span style='font-size:10.0pt;color:#333399'>良<span
lang=EN-US><o:p></o:p></span></span></p>
</td>
<td width=118 style='width:88.5pt;padding:0cm 0cm 0cm 0cm;height:36.0pt'>
<p class=MsoNormal><span style='font-size:10.0pt;color:#333399'>中<span
lang=EN-US><o:p></o:p></span></span></p>
</td>
<td width=123 style='width:92.25pt;padding:0cm 0cm 0cm 0cm;height:36.0pt'>
<p class=MsoNormal><span style='font-size:10.0pt;color:#333399'>及格<span
lang=EN-US><o:p></o:p></span></span></p>
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<td width=116 style='width:87.0pt;padding:0cm 0cm 0cm 0cm;height:36.0pt'>
<p class=MsoNormal><span style='font-size:10.0pt;color:#333399'>不及格<span
lang=EN-US><o:p></o:p></span></span></p>
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<p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;color:#333399'>80<span
style='letter-spacing:1.0pt'>≤mark＜90</span><o:p></o:p></span></p>
</td>
<td style='padding:0cm 0cm 0cm 0cm;height:31.5pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;color:#333399;
letter-spacing:1.0pt'>70≤mark＜80</span><span lang=EN-US style='font-size:
10.0pt;color:#333399'><o:p></o:p></span></p>
</td>
<td style='padding:0cm 0cm 0cm 0cm;height:31.5pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;color:#333399;
letter-spacing:1.0pt'>60≤mark＜70</span><span lang=EN-US style='font-size:
10.0pt;color:#333399'><o:p></o:p></span></p>
</td>
<td style='padding:0cm 0cm 0cm 0cm;height:31.5pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;color:#333399;
letter-spacing:1.0pt'>60≤mark＜70</span><span lang=EN-US style='font-size:
10.0pt;color:#333399'><o:p></o:p></span></p>
</td>
<td style='padding:0cm 0cm 0cm 0cm;height:31.5pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;color:#333399;
letter-spacing:1.0pt'>60＜mark</span><span lang=EN-US style='font-size:10.0pt;
color:#333399'><o:p></o:p></span></p>
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style='display:none;mso-hide:all'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
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<p style='layout-grid-mode:char'><span lang=EN-US> <o:p></o:p></span></p>
<p style='layout-grid-mode:char'><b><span lang=EN-US style='letter-spacing:
1.0pt'>3.</span></b><b><span lang=EN-US style='font-size:7.0pt;font-family:
"Times New Roman";letter-spacing:1.0pt'> </span><span style='letter-spacing:
1.0pt'>条件函数</span></b> <span lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><b><span style='letter-spacing:1.0pt'> （<span
lang=EN-US>1）if函数</span></span></b><span lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><span lang=EN-US style='letter-spacing:1.0pt'>
</span> <span style='letter-spacing:1.0pt'>函数形式： <b><span lang=EN-US
style='color:blue'>Iif（表达式，</span><span style='color:maroon'>当条件为<span
lang=EN-US>True时的值</span></span><span style='color:blue'>，</span><span
style='color:red'>当条件为<span lang=EN-US>False时的值<br>
</span></span></b>例：求<span lang=EN-US>X、Y中大的数，并放入变量Tmax中： <b>Tmax=Iif（X>Y,
X, Y）</b></span></span><span lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><b><span style='letter-spacing:1.0pt'> （<span
lang=EN-US>2）Choose函数</span></span></b><span lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><span lang=EN-US style='letter-spacing:1.0pt'>
</span> <span style='letter-spacing:1.0pt'>函数形式：<b><span lang=EN-US
style='color:blue'>Choose（整数表达式，选项列表）</span></b></span><span lang=EN-US><br>
<span style='letter-spacing:1.0pt'>如果整数表达式的值是1，则选择列表中的第1项，依次类推；如果小于1或大于列表项数时，则返回NULL。<br>
例： 根据nub为1 -4的值，换算成不同的运算符： <span style='color:maroon'>OP=<b> Choose（nub,“＋”，“－”，“×”，“÷”）</b></span></span><o:p></o:p></span></p>
<b><span lang=EN-US style='font-size:14.0pt;font-family:宋体;mso-bidi-font-family:
"Times New Roman";letter-spacing:1.0pt;mso-ansi-language:EN-US;mso-fareast-language:
ZH-CN;mso-bidi-language:AR-SA'><br clear=all style='page-break-before:always'>
</span></b>
<p align=center style='text-align:center;layout-grid-mode:char'><b><span
lang=EN-US style='font-size:14.0pt;letter-spacing:1.0pt'> 4.3 循环结构</span></b><span
lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><span style='letter-spacing:1.0pt'>循环是在指定的条件下多次重复执行一组语句。<span
lang=EN-US>VB中提供了两种类型的循环语句：</span></span><span lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><b><span style='letter-spacing:1.0pt'>计数循环语句</span></b><span
style='letter-spacing:1.0pt'>和<b>条件型循环语句</b></span> <span lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><b><span lang=EN-US style='letter-spacing:
1.0pt'>1.</span></b><b><span lang=EN-US style='font-size:7.0pt;fon⌨️ 快捷键说明
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