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<p style='layout-grid-mode:char'><b><span lang=EN-US style='color:blue;
letter-spacing:1.0pt'> 2）If <</span><span style='color:maroon;
letter-spacing:1.0pt'>表达式</span><span lang=EN-US style='color:blue;letter-spacing:
1.0pt'>> Then <</span><span style='color:red;letter-spacing:
1.0pt'>语句</span><span lang=EN-US style='color:blue;letter-spacing:1.0pt'>></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'>说明</span></b><span
style='letter-spacing:1.0pt'>：表达式一般为关系表达式、逻辑表达式，也可以为算术表达式，非<span lang=EN-US>0为True，0为False；</span></span><span
lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><span style='letter-spacing:1.0pt'>语句块可以是一句或多句，若用<span
lang=EN-US>2）表示，则只能是一句语句，若多句，语句间需用冒号分隔，而且必须在一行上书写。</span></span><span
lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'> <span style='letter-spacing:1.0pt'>例：已知两个数<span
lang=EN-US>x和y，比较它们的大小，使得 x大于y：</span></span><span lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><b> <span style='color:maroon;letter-spacing:
1.0pt'>方法一：<span lang=EN-US> if x<y then</span></span></b><span
lang=EN-US> <br>
<b><span style='color:maroon'> </span></b> <b><span
style='color:maroon;letter-spacing:1.0pt'>t=x<br>
x=y<br>
y=t<br>
end if</span></b><o:p></o:p></span></p>
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1.5pt' height=111>
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<p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;color:#333399'><!--[if gte vml 1]><v:shape
id="_x0000_i1049" type="#_x0000_t75" alt="" style='width:119.25pt;height:65.25pt'>
<v:imagedata src="./4-4.files/image020.gif" o:href="http://219.219.90.5/jcy/二级考试辅导资料/VB/vbweb/study/images/image430.gif"/>
</v:shape><![endif]--><![if !vml]><img width=159 height=87
src="./4-4.files/image020.gif"
tppabs="http://210.28.33.29/vbweb/study/images/image430.gif" v:shapes="_x0000_i1049"><![endif]><o:p></o:p></span></p>
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<p style='layout-grid-mode:char'><b><span style='color:blue;letter-spacing:
1.0pt'> 方法二：<span lang=EN-US> if x<y then t=x :
x=y : y=t</span></span></b><span lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><b><span style='color:red;letter-spacing:1.0pt'> 注意：</span></b><span
style='color:blue;letter-spacing:1.0pt'>将两个变量中的数进行交换时，必须借助于第三个变量才能实现。</span> <span
lang=EN-US><o:p></o:p></span></p>
<p style='margin-left:26.25pt;text-indent:-26.25pt;tab-stops:list 26.25pt;
layout-grid-mode:char'><b><span lang=EN-US style='letter-spacing:1.0pt'>(2）<span
style='color:#000099'>If</span>……Then……Else语句（双分支结构）</span></b><span
lang=EN-US> <br>
<strong> </strong> <strong><span style='letter-spacing:1.0pt'>语句形式： </span></strong><span
style='letter-spacing:1.0pt'>
</span> <br>
<b><span style='color:blue'> </span></b> <b><span style='color:blue;letter-spacing:
1.0pt'>1）If <</span><span style='color:maroon;letter-spacing:1.0pt'>表达式</span><span
style='color:blue;letter-spacing:1.0pt'>> Then</span></b><span
style='letter-spacing:1.0pt'> <br>
<span style='color:red'> </span> <strong><span style='color:red'><语句块1></span></strong><b><span
style='color:red'><br>
</span><strong><span style='color:blue'> </span></strong><span
style='color:blue'>Else<br>
</span><strong><span style='color:red'> <语句块2></span></strong></b></span><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>
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1.5pt;margin-left:26.25pt' height=203>
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<td style='padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;color:#333399'><!--[if gte vml 1]><v:shape
id="_x0000_i1050" type="#_x0000_t75" alt="" style='width:236.25pt;height:143.25pt'>
<v:imagedata src="./4-4.files/image021.gif" o:href="http://219.219.90.5/jcy/二级考试辅导资料/VB/vbweb/study/images/image431.gif"/>
</v:shape><![endif]--><![if !vml]><img width=315 height=191
src="./4-4.files/image021.gif"
tppabs="http://210.28.33.29/vbweb/study/images/image431.gif" v:shapes="_x0000_i1050"><![endif]><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='color:blue;letter-spacing:
1.0pt'>2） If <</span><span style='color:maroon;letter-spacing:1.0pt'>表达式</span><span
lang=EN-US style='color:blue;letter-spacing:1.0pt'>> Then <</span><span
style='color:red;letter-spacing:1.0pt'>语句<span lang=EN-US>1</span></span><span
lang=EN-US style='color:blue;letter-spacing:1.0pt'>> Else <</span><span
style='color:red;letter-spacing:1.0pt'>语句<span lang=EN-US>2</span></span><span
lang=EN-US style='color:blue;letter-spacing:1.0pt'>></span></b><span
lang=EN-US> <o:p></o:p></span></p>
<table border=0 cellpadding=0 width="33%" style='width:33.0%;mso-cellspacing:
1.5pt;margin-left:11.25pt'>
<tr>
<td width="9%" rowspan=2 style='width:9.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><b><span style='font-size:10.0pt;color:#333399;letter-spacing:
1.0pt'>例：</span></b><span lang=EN-US style='font-size:10.0pt;color:#333399'><o:p></o:p></span></p>
</td>
<td width="5%" rowspan=2 style='width:5.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;color:#333399'><!--[if gte vml 1]><v:shape
id="_x0000_i1051" type="#_x0000_t75" alt="" style='width:9.75pt;height:16.5pt'>
<v:imagedata src="./4-4.files/image022.gif" o:href="http://219.219.90.5/jcy/二级考试辅导资料/VB/vbweb/study/images/image434.gif"/>
</v:shape><![endif]--><![if !vml]><img width=13 height=22
src="./4-4.files/image023.gif"
tppabs="http://210.28.33.29/vbweb/study/images/image434.gif" v:shapes="_x0000_i1051"><![endif]><o:p></o:p></span></p>
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<td width="86%" style='width:86.0%;padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;color:#333399;
letter-spacing:1.0pt'>x<sup>2</sup> -5 x≠0</span></b><span
lang=EN-US style='font-size:10.0pt;color:#333399'> <o:p></o:p></span></p>
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<td style='padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;color:#333399;
letter-spacing:1.0pt'>3x +2 x=0</span></b><span lang=EN-US
style='font-size:10.0pt;color:#333399'><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>
<table border=0 cellpadding=0 width="32%" style='width:32.0%;mso-cellspacing:
1.5pt' height=226>
<tr>
<td style='padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;color:#333399'><!--[if gte vml 1]><v:shape
id="_x0000_i1052" type="#_x0000_t75" alt="" style='width:225pt;height:130.5pt'>
<v:imagedata src="./4-4.files/image024.jpg" o:href="http://219.219.90.5/jcy/二级考试辅导资料/VB/vbweb/study/images/image435.jpg"/>
</v:shape><![endif]--><![if !vml]><img width=300 height=174
src="./4-4.files/image024.jpg"
tppabs="http://210.28.33.29/vbweb/study/images/image435.jpg" v:shapes="_x0000_i1052"><![endif]><o:p></o:p></span></p>
</td>
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<td style='padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;color:#333399'><!--[if gte vml 1]><v:shape
id="_x0000_i1053" type="#_x0000_t75" alt="" style='width:60.75pt;height:85.5pt'>
<v:imagedata src="./4-4.files/image025.jpg" o:href="http://219.219.90.5/jcy/二级考试辅导资料/VB/vbweb/study/images/image432.jpg"/>
</v:shape><![endif]--><![if !vml]><img width=81 height=114
src="./4-4.files/image026.jpg"
tppabs="http://210.28.33.29/vbweb/study/images/image432.jpg" v:shapes="_x0000_i1053"><![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='margin-left:26.25pt;text-indent:-26.25pt;tab-stops:list 26.25pt;
layout-grid-mode:char'><b><span lang=EN-US style='letter-spacing:1.0pt'>(3)If……Then……ElseIf语句（多分支结构）</span></b><span
lang=EN-US> <br>
<strong><span style='letter-spacing:1.0pt'>语句形式：</span></strong><span
style='letter-spacing:1.0pt'>
<b><span style='color:blue'><br>
If <</span><span style='color:maroon'>表达式1</span><span
style='color:blue'>> Then</span></b> <br>
<span style='color:red'> </span> <span style='color:red'> <strong><语句块1></strong></span><b><span
style='color:blue'> <br>
ElseIf <</span><span style='color:maroon'>表达式2</span><span
style='color:blue'>> Then</span></b> <br>
<span style='color:red'> </span> <strong><span style='color:red'><语句块2></span></strong><span
style='color:red'><br>
<b> </b> </span><b><span style='color:blue'>……<br>
</span><span style='color:red'> </span><span style='color:blue'> </span><span
style='color:red'> [ </span><span style='color:blue'>Else </span></b><span
style='color:red'>语句块 n+1 <b>]</b></span></span> <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>
<table border=0 cellpadding=0 width="25%" style='width:25.0%;mso-cellspacing:
1.5pt;margin-left:26.25pt' height=131>
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<td style='padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;color:#333399'><!--[if gte vml 1]><v:shape
id="_x0000_i1054" type="#_x0000_t75" alt="" style='width:284.25pt;height:212.25pt'>
<v:imagedata src="./4-4.files/image027.gif" o:href="http://219.219.90.5/jcy/二级考试辅导资料/VB/vbweb/study/images/image436.gif"/>
</v:shape><![endif]--><![if !vml]><img width=379 height=283
src="./4-4.files/image027.gif"
tppabs="http://210.28.33.29/vbweb/study/images/image436.gif" v:shapes="_x0000_i1054"><![endif]><o:p></o:p></span></p>
</td>
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<p style='margin-left:26.25pt;text-indent:-26.25pt;tab-stops:list 26.25pt;
layout-grid-mode:char'><b><span style='letter-spacing:1.0pt'>注意</span></b> ： <span
lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><span style='letter-spacing:1.0pt'> <span
lang=EN-US>1）不管有几个分支，程序执行了一个分支后，其余分支不再执行；</span></span><span lang=EN-US><br>
<span style='letter-spacing:1.0pt'>2）<b>ElseIf</b> 不能写成<b><span
style='color:blue'>Else If</span></b></span> <br>
<span style='letter-spacing:1.0pt'>3）当多分支中有多个表达式同时满足，则只执行第一个与之匹配的语句块</span> <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'>：已知变量<span lang=EN-US>strC中存放了一个字符，判断该字符是字母字符、数字字符还是其他字符。</span></span>
<span lang=EN-US><o:p></o:p></span></p>
<table border=0 cellpadding=0 width="38%" style='width:38.0%;mso-cellspacing:
1.5pt'>
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<td style='padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;color:#333399'><!--[if gte vml 1]><v:shape
id="_x0000_i1055" type="#_x0000_t75" alt="" style='width:183.75pt;height:102.75pt'>
<v:imagedata src="./4-4.files/image028.jpg" o:href="http://219.219.90.5/jcy/二级考试辅导资料/VB/vbweb/study/images/image437.jpg"/>
</v:shape><![endif]--><![if !vml]><img width=245 height=137
src="./4-4.files/image028.jpg"
tppabs="http://210.28.33.29/vbweb/study/images/image437.jpg" v:shapes="_x0000_i1055"><![endif]><o:p></o:p></span></p>
</td>
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<td style='padding:.75pt .75pt .75pt .75pt'>
<p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;color:#333399'><!--[if gte vml 1]><v:shape
id="_x0000_i1056" type="#_x0000_t75" alt="" style='width:270pt;height:147pt'>
<v:imagedata src="./4-4.files/image029.jpg" o:href="http://219.219.90.5/jcy/二级考试辅导资料/VB/vbweb/study/images/image439.jpg"/>
</v:shape><![endif]--><![if !vml]><img width=360 height=196
src="./4-4.files/image029.jpg"
tppabs="http://210.28.33.29/vbweb/study/images/image439.jpg" v:shapes="_x0000_i1056"><![endif]><o:p></o:p></span></p>
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<p style='layout-grid-mode:char'><b><span style='letter-spacing:1.0pt'>（<span
lang=EN-US>4）</span></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'>If语句的嵌套</span></b><span lang=EN-US><o:p></o:p></span></p>
<p style='layout-grid-mode:char'><b><span lang=EN-US style='letter-spacing:
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