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| 58 | <span id="Expression-Statement"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="if-Statement.html" accesskey="n" rel="next">if Statement</a>, Up: <a href="Statements.html" accesskey="u" rel="up">Statements</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="Expression-Statement-1"></span><h3 class="section">19.1 Expression Statement</h3>
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| 64 | <span id="index-expression-statement"></span>
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| 65 | <span id="index-statement_002c-expression"></span>
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| 66 |
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| 67 | <p>The most common kind of statement in C is an <em>expression statement</em>.
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| 68 | It consists of an expression followed by a
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| 69 | semicolon. The expression’s value is discarded, so the expressions
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| 70 | that are useful are those that have side effects: assignment
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| 71 | expressions, increment and decrement expressions, and function calls.
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| 72 | Here are examples of expression statements:
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| 73 | </p>
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| 74 | <div class="example">
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| 75 | <pre class="example">x = 5; /* <span class="roman">Assignment expression.</span> */
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| 76 | p++; /* <span class="roman">Increment expression.</span> */
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| 77 | printf ("Done\n"); /* <span class="roman">Function call expression.</span> */
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| 78 | *p; /* <span class="roman">Cause <code>SIGSEGV</code> signal if <code>p</code> is null.</span> */
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| 79 | x + y; /* <span class="roman">Useless statement without effect.</span> */
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| 80 | </pre></div>
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| 81 |
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| 82 | <p>In very unusual circumstances we use an expression statement
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| 83 | whose purpose is to get a fault if an address is invalid:
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| 84 | </p>
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| 85 | <div class="example">
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| 86 | <pre class="example">volatile char *p;
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| 87 | <span class="roman">…</span>
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| 88 | *p; /* <span class="roman">Cause signal if <code>p</code> is null.</span> */
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| 89 | </pre></div>
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| 90 |
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| 91 | <p>If the target of <code>p</code> is not declared <code>volatile</code>, the
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| 92 | compiler might optimize away the memory access, since it knows that
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| 93 | the value isn’t really used. See <a href="volatile.html">volatile</a>.
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| 94 | </p>
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| 95 |
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| 96 |
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| 97 |
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