循环指令FOR NEXT

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<FONT size=3><FONT face=宋体>循环指令共有两条：循环区起点指令</FONT><SPAN lang=EN-US style="FONT-SIZE: 12pt">FOR</SPAN></FONT><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">，编号为</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">FNC08</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">，占</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">3</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">个程序步；循环结束指令</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">NEXT</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">，编号为</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">FNC09</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">，占用</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">1</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">个程序步，无操作数。</SPAN>
<P class=MsoNormal style="TEXT-INDENT: 24pt"><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">在程序运行时，位于</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">FOR</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">～</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">NEXT</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">间的程序反复执行</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">n</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">次（由操作数决定）后再继续执行后续程序。循环的次数</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">n=1</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">～</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">32767</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">。如果</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">N=-32767</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">～</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">0</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">之间，则当作</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">n=1</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">处理。</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 24pt"><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">如图</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">1</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">所示为一个二重嵌套循环，外层执行</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">5</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">次。如果</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">D0Z</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">中的数为</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">6</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">，则外层</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">A</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">每执行一次则内层</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">B</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">将执行</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">6</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">次。</SPAN></P>
<P class=MsoNormal style="TEXT-ALIGN: center" align=center><SPAN lang=EN-US style="FONT-SIZE: 12pt"><?xml:namespace prefix = v ns = "urn:schemas-microsoft-com:vml" /><v:shapetype id=_x0000_t75 path=" m@4@5 l@4@11@9@11@9@5 xe" stroked="f" filled="f" o:spt="75" o:preferrelative="t" coordsize="21600,21600"><v:stroke joinstyle="miter"></v:stroke><v:formulas><v:f eqn="if lineDrawn pixelLineWidth 0 "></v:f><v:f eqn="sum @0 1 0 "></v:f><v:f eqn="sum 0 0 @1 "></v:f><v:f eqn="prod @2 1 2 "></v:f><v:f eqn="prod @3 21600 pixelWidth "></v:f><v:f eqn="prod @3 21600 pixelHeight "></v:f><v:f eqn="sum @0 0 1 "></v:f><v:f eqn="prod @6 1 2 "></v:f><v:f eqn="prod @7 21600 pixelWidth "></v:f><v:f eqn="sum @8 21600 0 "></v:f><v:f eqn="prod @7 21600 pixelHeight "></v:f><v:f eqn="sum @10 21600 0 "></v:f></v:formulas><v:path o:connecttype="rect" gradientshapeok="t" o:extrusionok="f"></v:path><?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:lock v:ext="edit" aspectratio="t"></o:lock></v:shapetype><IMG src="attachment.asp?path=UploadFiles/2007-11/12730658953.jpg"></SPAN></P>
<P class=MsoNormal style="TEXT-ALIGN: center" align=center><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">图</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">1&nbsp; </SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">循环指令的使用</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 24pt"><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">使用循环指令时应注意：</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 39pt; TEXT-INDENT: -18pt"><SPAN lang=EN-US style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">1）</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">FOR</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">和</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">NEXT</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">必须成对使用；</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 24pt"><SPAN lang=EN-US style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">2</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">）</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">FX2N</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">系列</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">PLC</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">可循环嵌套</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">5</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">层；</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 24pt"><SPAN lang=EN-US style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">3</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">）</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">在循环中可利用</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">CJ</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">指令在循环没结束时跳出循环体；</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 24pt"><SPAN lang=EN-US style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">4</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">）</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">FOR</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">应放在</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">NEXT</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">之前，</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">NEXT</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">应在</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">FEND</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">和</SPAN><SPAN lang=EN-US style="FONT-SIZE: 12pt">END</SPAN><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体">之前，否则均会出错。<BR></SPAN></P>