3240593d2e
Исправлена ошибка for step Дополнена справка по for step и foreach index J,yjdkty ntrcnjdsq htlfrnjh? gjlcdtxbdf.obq ыеуз b штвуч rjyntrcnyj d hfvrf[ jlyjq cnhjrb
123 lines
5.7 KiB
HTML
123 lines
5.7 KiB
HTML
<html>
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<head>
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<object type="application/x-oleobject" classid="clsid:1e2a7bd0-dab9-11d0-b93a-00c04fc99f9e">
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<param name="Keyword" value="for">
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<param name="Keyword" value="to">
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<param name="Keyword" value="downto">
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<param name="Keyword" value="do">
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<param name="Keyword" value="step">
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</object>
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<meta http-equiv="Content-Type" content="text/html; charset=windows-1251">
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<title></title>
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<link rel="StyleSheet" href="../../default.css">
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<style type="text/css">
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.auto-style1 {
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color: #FF0000;
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}
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</style>
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</head>
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<body>
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<H1>Îïåðàòîð öèêëà for</H1>
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<p>Îïåðàòîð öèêëà <code><b>for</b></code> èìååò îäíó èç äâóõ
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ôîðì:</p>
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<blockquote>
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<p><code><b>for</b> </code><code class="codeit">ïåðåìåííàÿ</code><code> :=</code><code>
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</code><code class="codeit">íà÷àëüíîå
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çíà÷åíèå</code><code> <b>to</b> </code><code class="codeit">êîíå÷íîå
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çíà÷åíèå</code><code> <b>do</b><br>
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</code><code class="codeit">îïåðàòîð</code></p>
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</blockquote>
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<p>èëè</p>
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<blockquote>
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<p><code><b>for</b> </code><code class="codeit">ïåðåìåííàÿ</code><code> :=
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</code><code class="codeit">íà÷àëüíîå
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çíà÷åíèå</code><code> <b>downto</b> </code><code class="codeit">êîíå÷íîå
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çíà÷åíèå</code><code> <b>do</b><br>
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</code><code class="codeit">îïåðàòîð</code></p>
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</blockquote>
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<p>Êðîìå òîãî, ïåðåìåííóþ ìîæíî îïèñàòü íåïîñðåäñòâåííî â
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çàãîëîâêå öèêëà:</p>
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<blockquote>
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<p><code><b>for</b> </code><code class="codeit">ïåðåìåííàÿ</code><code>:</code><code class="codeit"> òèï</code><code> := </code><code class="codeit">íà÷àëüíîå
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çíà÷åíèå</code><code> <b>to</b> </code><code class="codeit">èëè</code><code><span lang="ru">
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</span> <b>downto</b> </code><code class="codeit">êîíå÷íîå
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çíà÷åíèå</code><code> <b>do</b><br>
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</code><code class="codeit">îïåðàòîð</code></p>
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</blockquote>
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<p>èëè</p>
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<blockquote>
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<p><code><b>for var</b> </code><code class="codeit">ïåðåìåííàÿ</code><code> :=
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</code><code class="codeit">íà÷àëüíîå
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çíà÷åíèå</code><code> <b>to</b> </code><code class="codeit">èëè</code><code><span lang="ru">
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</span> <b>downto</b> </code><code class="codeit">êîíå÷íîå
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çíà÷åíèå</code><code> <b>do</b><br>
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</code><code class="codeit">îïåðàòîð</code></p>
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</blockquote>
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<p> ïîñëåäíåì ñëó÷àå èñïîëüçóåòñÿ <em><strong><span class="auto-style1">àâòîîïðåäåëåíèå òèïà</span></strong></em>
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ïåðåìåííîé ïî òèïó íà÷àëüíîãî çíà÷åíèÿ.  äâóõ ïîñëåäíèõ ñëó÷àÿõ îáëàñòü äåéñòâèÿ
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îáúÿâëåííîé ïåðåìåííîé ðàñïðîñòðàíÿåòñÿ äî êîíöà òåëà öèêëà, êîòîðîå â äàííîì ñëó÷àå
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îáðàçóåò íåÿâíûé áëîê. Âíå òåëà öèêëà òàêàÿ ïåðåìåííàÿ íåäîñòóïíà, ïîýòîìó
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ñëåäóþùèé öèêë ìîæåò èñïîëüçîâàòü ïåðåìåííóþ ñ òåì æå èìåíåì:</p>
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<blockquote>
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<p><code><b>for</b> <strong>var</strong> i := 1 <b>to</b> 10 <b>do<br></b>
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Print(i);<br>
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<b>for</b> <strong>var </strong>i := 1 <b>to</b> 5 <b>do</b><br>
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Print(i*i);</code></p>
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</blockquote>
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<p>Íàêîíåö, â çàãîëîâêå öèêëà for ìîæíî óêàçàòü øàã èçìåíåíèÿ öèêëà:</p>
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<blockquote>
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<p><code><b>for var</b> </code><code class="codeit">ïåðåìåííàÿ</code><code> :=
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</code><code class="codeit">íà÷àëüíîå
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çíà÷åíèå</code><code> <b>to</b> </code><code class="codeit">êîíå÷íîå
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çíà÷åíèå</code><code> <b>step </b><code class="codeit">çíà÷åíèå<b> </b></code> <b>do</b><br>
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</code><code class="codeit">îïåðàòîð</code></p>
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</blockquote>
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<p>Ïðè íàëè÷èè øàãà öèêëà ðàçðåøàåòñÿ èñïîëüçîâàòü òîëüêî íàïðàâëåíèå <code> <b>to</b></code>. </p>
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<p>Øàã <code> <b>step</b></code> ìîæåò áûòü îòðèöàòåëüíûì. Åñëè øàã <code> <b>
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step</b></code> ðàâåí íóëþ, âîçíèêàåò îøèáêà âðåìåíè âûïîëíåíèÿ ïðîãðàììû.</p>
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<p>Òåêñò îò ñëîâà <code><b>for</b></code> äî ñëîâà <code><b>do</b></code>
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âêëþ÷èòåëüíî íàçûâàåòñÿ <b><font color="#FF0000"> <i>çàãîëîâêîì öèêëà</i></font></b>, à
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îïåðàòîð ïîñëå <code><b>do</b></code> - <i><b><font color="#FF0000">òåëîì öèêëà</font></b>.</i>
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Ïåðåìåííàÿ ïîñëå ñëîâà <code><b>for</b></code> íàçûâàåòñÿ <i><b>
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<font color="#FF0000">ïàðàìåòðîì öèêëà</font></b></i>.
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Äëÿ ïåðâîé ôîðìû öèêëà ñ êëþ÷åâûì ñëîâîì <code><b>to</b></code>
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ïàðàìåòð öèêëà ìåíÿåòñÿ îò íà÷àëüíîãî çíà÷åíèÿ äî
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êîíå÷íîãî çíà÷åíèÿ, óâåëè÷èâàÿñü âñÿêèé ðàç íà åäèíèöó, à äëÿ
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âòîðîé ôîðìû êëþ÷åâûì ñëîâîì <code><b>downto</b></code> -
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óìåíüøàÿñü íà åäèíèöó. Äëÿ êàæäîãî çíà÷åíèÿ ïåðåìåííîé-ïàðàìåòðà
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âûïîëíÿåòñÿ òåëî öèêëà. Îäíîêðàòíîå ïîâòîðåíèå òåëà öèêëà
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íàçûâàåòñÿ <i><b><font color="#FF0000">èòåðàöèåé öèêëà</font></b></i>. Çíà÷åíèå ïàðàìåòðà öèêëà ïîñëå çàâåðøåíèÿ öèêëà ñ÷èòàåòñÿ íåîïðåäåëåííûì.</p>
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<p>Ïåðåìåííàÿ-ïàðàìåòð öèêëà ìîæåò èìåòü ëþáîé <a href="../Types/index_types.html">ïîðÿäêîâûé òèï</a>. Ïðè ýòîì íà÷àëüíîå è
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êîíå÷íîå çíà÷åíèÿ äîëæíû áûòü <a href="../Types/typecompatibility.html">
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ñîâìåñòèìû ïî ïðèñâàèâàíèþ</a> ñ ïåðåìåííîé-ïàðàìåòðîì öèêëà. </p>
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<p>Íàïðèìåð:</p>
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<blockquote>
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<p><code><b>var</b> en: (red,green,blue,white);<b><br>
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...<br>
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for</b> en := red <b>to</b> blue <b>do</b><br>
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write(Ord(en):2);<br>
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<b>for</b> <b>var</b> c := 'a' <b>to</b> 'z' <b>step</b> 2 <b>do</b><br>
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write(c);</code></p>
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</blockquote>
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<p>Åñëè äëÿ öèêëà <code><b>for</b></code> ... <code><b>to</b></code>
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íà÷àëüíîå çíà÷åíèå ïåðåìåííîé öèêëà áîëüøå êîíå÷íîãî çíà÷åíèÿ
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èëè äëÿ öèêëà <code><b>for</b></code> ...
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<code><b>downto</b></code> íà÷àëüíîå çíà÷åíèå ïåðåìåííîé öèêëà
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ìåíüøå êîíå÷íîãî çíà÷åíèÿ, òî òåëî öèêëà íå âûïîëíèòñÿ íè ðàçó.</p>
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<p>Åñëè öèêë èñïîëüçóåòñÿ â ïîäïðîãðàììå, òî
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ïåðåìåííàÿ-ïàðàìåòð öèêëà äîëæíà áûòü îïèñàíà êàê ëîêàëüíàÿ. Íàèëó÷øèì ðåøåíèåì
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â PascalABC.NET ÿâëÿåòñÿ îïèñàíèå ïåðåìåííîé â çàãîëîâêå öèêëà.</p>
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<p>Èçìåíåíèå ïåðåìåííîé-ïàðàìåòðà öèêëà âíóòðè öèêëà ÿâëÿåòñÿ
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ëîãè÷åñêîé îøèáêîé. Íàïðèìåð, ñëåäóþùèé ôðàãìåíò ñî âëîæåííûì îïåðàòîðîì
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<code><b>for</b></code> ÿâëÿåòñÿ îøèáî÷íûì:</p>
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<blockquote>
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<p><code><b>for</b> i := 1 <b>to</b> 10 <b>do</b><br>
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i -= 1;</code></p>
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</blockquote>
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<p> </p>
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</body>
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</html>
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