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| 22 | <title>Floating 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="Imaginary-Constants.html" rel="next" title="Imaginary Constants">
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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="Floating-Constants"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Imaginary-Constants.html" accesskey="n" rel="next">Imaginary Constants</a>, Previous: <a href="Integer-Const-Type.html" accesskey="p" rel="prev">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="Floating_002dPoint-Constants"></span><h3 class="section">12.3 Floating-Point Constants</h3>
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| 64 | <span id="index-floating_002dpoint-constants"></span>
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| 65 | <span id="index-constants_002c-floating_002dpoint"></span>
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| 66 |
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| 67 | <p>A floating-point constant must have either a decimal point, an
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| 68 | exponent-of-ten, or both; they distinguish it from an integer
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| 69 | constant.
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| 70 | </p>
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| 71 | <p>To indicate an exponent, write ‘<samp>e</samp>’ or ‘<samp>E</samp>’. The exponent
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| 72 | value follows. It is always written as a decimal number; it can
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| 73 | optionally start with a sign. The exponent <var>n</var> means to multiply
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| 74 | the constant’s value by ten to the <var>n</var>th power.
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| 75 | </p>
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| 76 | <p>Thus, ‘<samp>1500.0</samp>’, ‘<samp>15e2</samp>’, ‘<samp>15e+2</samp>’, ‘<samp>15.0e2</samp>’,
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| 77 | ‘<samp>1.5e+3</samp>’, ‘<samp>.15e4</samp>’, and ‘<samp>15000e-1</samp>’ are six ways of
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| 78 | writing a floating-point number whose value is 1500. They are all
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| 79 | equivalent.
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| 80 | </p>
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| 81 | <p>Here are more examples with decimal points:
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| 82 | </p>
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| 83 | <div class="example">
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| 84 | <pre class="example">1.0
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| 85 | 1000.
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| 86 | 3.14159
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| 87 | .05
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| 88 | .0005
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| 89 | </pre></div>
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| 90 |
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| 91 | <p>For each of them, here are some equivalent constants written with
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| 92 | exponents:
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| 93 | </p>
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| 94 | <div class="example">
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| 95 | <pre class="example">1e0, 1.0000e0
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| 96 | 100e1, 100e+1, 100E+1, 1e3, 10000e-1
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| 97 | 3.14159e0
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| 98 | 5e-2, .0005e+2, 5E-2, .0005E2
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| 99 | .05e-2
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| 100 | </pre></div>
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| 101 |
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| 102 | <p>A floating-point constant normally has type <code>double</code>. You can
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| 103 | force it to type <code>float</code> by adding ‘<samp>f</samp>’ or ‘<samp>F</samp>’
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| 104 | at the end. For example,
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| 105 | </p>
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| 106 | <div class="example">
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| 107 | <pre class="example">3.14159f
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| 108 | 3.14159e0f
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| 109 | 1000.f
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| 110 | 100E1F
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| 111 | .0005f
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| 112 | .05e-2f
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| 113 | </pre></div>
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| 114 |
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| 115 | <p>Likewise, ‘<samp>l</samp>’ or ‘<samp>L</samp>’ at the end forces the constant
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| 116 | to type <code>long double</code>.
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| 117 | </p>
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| 118 | <p>You can use exponents in hexadecimal floating constants, but since
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| 119 | ‘<samp>e</samp>’ would be interpreted as a hexadecimal digit, the character
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| 120 | ‘<samp>p</samp>’ or ‘<samp>P</samp>’ (for “power”) indicates an exponent.
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| 121 | </p>
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| 122 | <p>The exponent in a hexadecimal floating constant is a possibly-signed
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| 123 | decimal integer that specifies a power of 2 (<em>not</em> 10 or 16) to
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| 124 | multiply into the number.
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| 125 | </p>
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| 126 | <p>Here are some examples:
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| 127 | </p>
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| 128 | <div class="example">
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| 129 | <pre class="example">0xAp2 // <span class="roman">40 in decimal</span>
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| 130 | 0xAp-1 // <span class="roman">5 in decimal</span>
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| 131 | 0x2.0Bp4 // <span class="roman">16.75 decimal</span>
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| 132 | 0xE.2p3 // <span class="roman">121 decimal</span>
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| 133 | 0x123.ABCp0 // <span class="roman">291.6708984375 in decimal</span>
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| 134 | 0x123.ABCp4 // <span class="roman">4666.734375 in decimal</span>
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| 135 | 0x100p-8 // <span class="roman">1</span>
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| 136 | 0x10p-4 // <span class="roman">1</span>
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| 137 | 0x1p+4 // <span class="roman">16</span>
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| 138 | 0x1p+8 // <span class="roman">256</span>
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| 139 | </pre></div>
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| 140 |
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| 141 | <p>See <a href="Floating_002dPoint-Data-Types.html">Floating-Point Data Types</a>.
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| 142 | </p>
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| 143 | <hr>
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| 144 | <div class="header">
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| 145 | <p>
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| 146 | Next: <a href="Imaginary-Constants.html" accesskey="n" rel="next">Imaginary Constants</a>, Previous: <a href="Integer-Const-Type.html" accesskey="p" rel="prev">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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