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| 22 | <title>Integer Constants (GNU C Language Manual)</title>
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| 31 | <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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| 32 | <link href="Constants.html" rel="up" title="Constants">
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| 33 | <link href="Integer-Const-Type.html" rel="next" title="Integer Const Type">
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| 55 | </head>
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| 56 |
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| 57 | <body lang="en">
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| 58 | <span id="Integer-Constants"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Integer-Const-Type.html" accesskey="n" rel="next">Integer Const Type</a>, Up: <a href="Constants.html" accesskey="u" rel="up">Constants</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="Integer-Constants-1"></span><h3 class="section">12.1 Integer Constants</h3>
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| 64 | <span id="index-integer-constants"></span>
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| 65 | <span id="index-constants_002c-integer"></span>
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| 66 |
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| 67 | <p>An integer constant consists of a number to specify the value,
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| 68 | followed optionally by suffix letters to specify the data type.
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| 69 | </p>
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| 70 | <p>The simplest integer constants are numbers written in base 10
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| 71 | (decimal), such as <code>5</code>, <code>77</code>, and <code>403</code>. A decimal
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| 72 | constant cannot start with the character ‘<samp>0</samp>’ (zero) because
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| 73 | that makes the constant octal.
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| 74 | </p>
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| 75 | <p>You can get the effect of a negative integer constant by putting a
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| 76 | minus sign at the beginning. Grammatically speaking, that is an
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| 77 | arithmetic expression rather than a constant, but it behaves just like
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| 78 | a true constant.
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| 79 | </p>
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| 80 | <p>Integer constants can also be written in octal (base 8), hexadecimal
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| 81 | (base 16), or binary (base 2). An octal constant starts with the
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| 82 | character ‘<samp>0</samp>’ (zero), followed by any number of octal digits
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| 83 | (‘<samp>0</samp>’ to ‘<samp>7</samp>’):
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| 84 | </p>
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| 85 | <div class="example">
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| 86 | <pre class="example">0 // <span class="roman">zero</span>
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| 87 | 077 // <span class="roman">63</span>
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| 88 | 0403 // <span class="roman">259</span>
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| 89 | </pre></div>
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| 90 |
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| 91 | <p>Pedantically speaking, the constant <code>0</code> is an octal constant, but
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| 92 | we can think of it as decimal; it has the same value either way.
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| 93 | </p>
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| 94 | <p>A hexadecimal constant starts with ‘<samp>0x</samp>’ (upper or lower case)
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| 95 | followed by hex digits (‘<samp>0</samp>’ to ‘<samp>9</samp>’, as well as ‘<samp>a</samp>’
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| 96 | through ‘<samp>f</samp>’ in upper or lower case):
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| 97 | </p>
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| 98 | <div class="example">
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| 99 | <pre class="example">0xff // <span class="roman">255</span>
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| 100 | 0XA0 // <span class="roman">160</span>
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| 101 | 0xffFF // <span class="roman">65535</span>
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| 102 | </pre></div>
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| 103 |
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| 104 | <span id="index-binary-integer-constants"></span>
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| 105 | <p>A binary constant starts with ‘<samp>0b</samp>’ (upper or lower case) followed
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| 106 | by bits (each represented by the characters ‘<samp>0</samp>’ or ‘<samp>1</samp>’):
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| 107 | </p>
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| 108 | <div class="example">
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| 109 | <pre class="example">0b101 // <span class="roman">5</span>
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| 110 | </pre></div>
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| 111 |
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| 112 | <p>Binary constants are a GNU C extension, not part of the C standard.
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| 113 | </p>
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| 114 | <p>Sometimes a space is needed after an integer constant to avoid
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| 115 | lexical confusion with the following tokens. See <a href="Invalid-Numbers.html">Invalid Numbers</a>.
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| 116 | </p>
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| 117 | <hr>
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| 118 | <div class="header">
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| 119 | <p>
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| 120 | Next: <a href="Integer-Const-Type.html" accesskey="n" rel="next">Integer Const Type</a>, Up: <a href="Constants.html" accesskey="u" rel="up">Constants</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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