63 lines
2.2 KiB
HTML
63 lines
2.2 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="while">
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<param name="Keyword" value="repeat">
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<param name="Keyword" value="until">
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<param name="Keyword" value="do">
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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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</head>
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<body>
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<H1>Îïåðàòîðû öèêëà while è repeat</H1>
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Îïåðàòîð öèêëà
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<code><b>while</b></code> èìååò ñëåäóþùóþ ôîðìó:<blockquote>
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<p><code><b>while</b> </code><code class="codeit">óñëîâèå</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><code class="codeit">Óñëîâèå</code> ïðåäñòàâëÿåò ñîáîé
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âûðàæåíèå ëîãè÷åñêîãî òèïà, à îïåðàòîð ïîñëå <code><b>do</b></code>
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íàçûâàåòñÿ <i>òåëîì öèêëà</i>. Ïåðåä êàæäîé èòåðàöèåé öèêëà
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óñëîâèå âû÷èñëÿåòñÿ, è åñëè îíî èñòèííî, òî âûïîëíÿåòñÿ òåëî öèêëà, â ïðîòèâíîì
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ñëó÷àå ïðîèñõîäèò âûõîä èç öèêëà.</p>
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<p>Åñëè <i>óñëîâèå</i> âñåãäà îêàçûâàåòñÿ èñòèííûì, òî ìîæåò ïðîèçîéòè
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<i>çàöèêëèâàíèå</i>: </p>
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<blockquote>
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<p><code><b>while</b> 2>1 <b>do<br>
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</b> write(1);</code></p>
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</blockquote>
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<p>Îïåðàòîð öèêëà <b><code>repeat</code></b> èìååò ñëåäóþùóþ ôîðìó:
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</p>
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<blockquote>
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<p><code><b>repeat<br>
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</b> </code><code class="codeit">îïåðàòîðû<br>
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</code><b><code>until</code></b> <code class="codeit">óñëîâèå</code></p>
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</blockquote>
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<p> îòëè÷èå îò öèêëà <code><b>while</b></code>,
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óñëîâèå âû÷èñëÿåòñÿ ïîñëå î÷åðåäíîé èòåðàöèè öèêëà, è åñëè îíî èñòèííî, òî ïðîèñõîäèò âûõîä èç öèêëà.
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Òàêèì îáðàçîì, îïåðàòîðû, îáðàçóþùèå òåëî öèêëà îïåðàòîðà <b><code>repeat</code></b>,
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âûïîëíÿþòñÿ ïî êðàéíåé ìåðå îäèí ðàç.</p>
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<p>Îáû÷íî îïåðàòîð repeat èñïîëüçóþò â ñèòóàöèÿõ, ãäå
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óñëîâèå íåëüçÿ ïðîâåðèòü, íå âûïîëíèâ òåëî öèêëà. Íàïðèìåð:</p>
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<blockquote>
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<p><code><b>repeat</b><br>
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read(x);<br>
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<b>until</b> x=0;</code></p>
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</blockquote>
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<p>Åñëè <i>óñëîâèå</i> âñåãäà îêàçûâàåòñÿ ëîæíûì, òî ìîæåò ïðîèçîéòè
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<i>çàöèêëèâàíèå</i>: </p>
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<blockquote>
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<p><code><b>repeat<br>
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</b> write(1);<br>
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<b>until</b> 2=1;</code></p>
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</blockquote>
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</body>
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</html>
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