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| 22 | <title>Logicals and Assignments (GNU C Language Manual)</title>
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| 30 | <link href="Symbol-Index.html" rel="index" title="Symbol Index">
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| 31 | <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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| 32 | <link href="Execution-Control-Expressions.html" rel="up" title="Execution Control Expressions">
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| 33 | <link href="Conditional-Expression.html" rel="next" title="Conditional Expression">
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| 57 | <body lang="en">
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| 58 | <span id="Logicals-and-Assignments"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Conditional-Expression.html" accesskey="n" rel="next">Conditional Expression</a>, Previous: <a href="Logicals-and-Comparison.html" accesskey="p" rel="prev">Logicals and Comparison</a>, Up: <a href="Execution-Control-Expressions.html" accesskey="u" rel="up">Execution Control Expressions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Index.html" title="Index" rel="index">Index</a>]</p>
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| 61 | </div>
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| 62 | <hr>
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| 63 | <span id="Logical-Operators-and-Assignments"></span><h3 class="section">8.3 Logical Operators and Assignments</h3>
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| 64 |
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| 65 | <p>There are cases where assignments nested inside the condition can
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| 66 | actually make a program <em>easier</em> to read. Here is an example
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| 67 | using a hypothetical type <code>list</code> which represents a list; it
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| 68 | tests whether the list has at least two links, using hypothetical
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| 69 | functions, <code>nonempty</code> which is true of the argument is a nonempty
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| 70 | list, and <code>list_next</code> which advances from one list link to the
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| 71 | next. We assume that a list is never a null pointer, so that the
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| 72 | assignment expressions are always “true.”
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| 73 | </p>
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| 74 | <div class="example">
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| 75 | <pre class="example">if (nonempty (list)
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| 76 | && (temp1 = list_next (list))
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| 77 | && nonempty (temp1)
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| 78 | && (temp2 = list_next (temp1)))
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| 79 | <span class="roman">…</span> /* <span class="roman">use <code>temp1</code> and <code>temp2</code></span> */
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| 80 | </pre></div>
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| 81 |
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| 82 | <p>Here we get the benefit of the ‘<samp>&&</samp>’ operator, to avoid executing
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| 83 | the rest of the code if a call to <code>nonempty</code> says “false.” The
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| 84 | only natural place to put the assignments is among those calls.
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| 85 | </p>
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| 86 | <p>It would be possible to rewrite this as several statements, but that
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| 87 | could make it much more cumbersome. On the other hand, when the test
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| 88 | is even more complex than this one, splitting it into multiple
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| 89 | statements might be necessary for clarity.
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| 90 | </p>
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| 91 | <p>If an empty list is a null pointer, we can dispense with calling
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| 92 | <code>nonempty</code>:
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| 93 | </p>
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| 94 | <div class="example">
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| 95 | <pre class="example">if ((temp1 = list_next (list))
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| 96 | && (temp2 = list_next (temp1)))
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| 97 | <span class="roman">…</span>
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| 98 | </pre></div>
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| 99 |
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| 100 |
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| 101 |
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| 102 |
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| 103 | </body>
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| 104 | </html>
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