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📁 关于 C++ 的历史无须我来介绍了
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  <title>递增、递减、指定运算</title>
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<h3><a href="http://caterpillar.onlyfun.net/GossipCN/index.html">From
Gossip@caterpillar</a></h3>

<h1><a href="CppGossip.html">C++ Gossip:&nbsp;递增、递减、指定运算</a></h1>

在程式中对变数递增1或递减1是很常见的运算，例如： <br>

<div style="margin-left: 40px;"><span style="font-weight: bold; font-family: Courier New,Courier,monospace;">int i = 0; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">i = i + 1; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">cout &lt;&lt; i
&lt;&lt; endl;</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">i = i - 1; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">cout &lt;&lt; i
&lt;&lt; endl;</span><br>

</div>

<br>

这段程式会分别显示出1与0两个数，您也可以这么写这个程式：<br>

<div style="margin-left: 40px;"><span style="font-weight: bold; font-family: Courier New,Courier,monospace;">int i = 0; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">cout &lt;&lt; ++i
&lt;&lt; endl;</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">cout &lt;&lt; --i
&lt;&lt; endl;</span><br>

</div>

<br>

其中写在变数 i 之前的++与--就是C++的“递增运算子”（Increment operator）与“递减运算子”（Decrement
operator），当它们撰写在变数之前时，其作用就相当于将变数递增1与递减1： <br>

<div style="margin-left: 40px;"><span style="font-weight: bold; font-family: Courier New,Courier,monospace;">++i;&nbsp; &nbsp; // i
= i + 1; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">--i;&nbsp; &nbsp;
&nbsp; // i = i - 1;</span><br>

</div>

<br>

您可以将递增或递减运算子撰写在变数之前或变数之后，但其实两者是有差别的，将递增（递减）运算子撰写在变数前时，表示先将变数的值加（减）1，然后再传
回变数的值，将递增（递减）运算子撰写在变数之后，表示先传回变数值，然后再对变数加（减）1，例如： <br>

<div style="margin-left: 40px;"><span style="font-weight: bold; font-family: Courier New,Courier,monospace;">int i = 0; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">int num = 0; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">num = ++i;&nbsp;
&nbsp;// 相当于i = i + 1; num = i; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">cout &lt;&lt; num
&lt;&lt; endl; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">num = --i;&nbsp;
&nbsp; // 相当于i = i - 1; num = i; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">cout &lt;&lt; num
&lt;&lt; endl;</span><br>

</div>

<br>

在这段程式中，num的值会前后分别显示为1与0，再看看下面这段：<br>

<div style="margin-left: 40px;"><span style="font-weight: bold; font-family: Courier New,Courier,monospace;">int i = 0; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">int num = 0; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">num = i++;&nbsp;
&nbsp; // 相当于num = i; i = i + 1; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">cout &lt;&lt; num
&lt;&lt; endl;</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">num = i--;&nbsp;
&nbsp; &nbsp;// 相当于 num = i; i = i - 1; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">cout &lt;&lt; num
&lt;&lt; endl;</span><br>

</div>

<br>

在这段程式中，num的值会显示前后分别为0与1。 <br>

<br>

接下来看“指定运算子”（Assignment
operator），到目前为止我们只看过一个指定运算子，也就是=这个运算子，事实上指定运算子还有以下的几个： <br>

<br>

<table style="text-align: left; width: 50%;" border="1" cellpadding="2" cellspacing="2">

  <tbody>

    <tr>

      <td style="background-color: rgb(204, 204, 204);"><small>运算子</small></td>

      <td style="background-color: rgb(204, 204, 204);"><small>例子</small></td>

      <td style="background-color: rgb(204, 204, 204);"><small>说明</small></td>

    </tr>

    <tr>

      <td style="font-family: Courier New,Courier,monospace;"><small>+=</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a += b&nbsp;</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a = a + b</small></td>

    </tr>

    <tr>

      <td style="font-family: Courier New,Courier,monospace;"><small>-=</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a -= b</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a = a - b</small></td>

    </tr>

    <tr>

      <td style="font-family: Courier New,Courier,monospace;"><small>*=</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a *= b</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a = a * b</small></td>

    </tr>

    <tr>

      <td style="font-family: Courier New,Courier,monospace;"><small>/=</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a /= b</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a = a / b</small></td>

    </tr>

    <tr>

      <td style="font-family: Courier New,Courier,monospace;"><small>%=</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a %= b</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a = a % b</small></td>

    </tr>

    <tr>

      <td style="font-family: Courier New,Courier,monospace;"><small>&amp;=</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a &amp;= b</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a = a &amp; b</small></td>

    </tr>

    <tr>

      <td style="font-family: Courier New,Courier,monospace;"><small>|=</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a |= b</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a = a | b</small></td>

    </tr>

    <tr>

      <td style="font-family: Courier New,Courier,monospace;"><small>^=</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a ^= b</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a = a ^ b</small></td>

    </tr>

    <tr>

      <td style="font-family: Courier New,Courier,monospace;"><small>&lt;&lt;=</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a &lt;&lt;= b</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a = a &lt;&lt; b</small></td>

    </tr>

    <tr>

      <td style="font-family: Courier New,Courier,monospace;"><small>&gt;&gt;=</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a &gt;&gt;= b</small></td>

      <td style="font-family: Courier New,Courier,monospace;"><small>a = a &gt;&gt; b</small></td>

    </tr>

  
  </tbody>
</table>

<br>

就单一个陈述而言，使用++、--或指定运算子是还算可以理解，但与其它陈述结合时可就得考虑一下，例如：<br>

<div style="margin-left: 40px;"><span style="font-weight: bold; font-family: Courier New,Courier,monospace;">int i = 5; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">

<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">arr[--i %= 10] =
10;</span><br>

</div>

<br>

像这样的式子，i
是多少，以及阵列的指定索引位置在哪可就得想一下了（有兴趣算一下的话，i会是4，而阵列的指定索引也是4），总之，如何使用与何时使用，自己得拿捏着
点。 <br>

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