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| 22 | <title>Array Example Call (GNU C Language Manual)</title>
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| 23 |
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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="Beyond-Integers.html" rel="up" title="Beyond Integers">
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| 33 | <link href="Array-Example-Variations.html" rel="next" title="Array Example Variations">
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| 38 | blockquote.indentedblock {margin-right: 0em}
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| 39 | div.display {margin-left: 3.2em}
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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="Array-Example-Call"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Array-Example-Variations.html" accesskey="n" rel="next">Array Example Variations</a>, Previous: <a href="Array-Example.html" accesskey="p" rel="prev">Array Example</a>, Up: <a href="Beyond-Integers.html" accesskey="u" rel="up">Beyond Integers</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="Calling-the-Array-Example"></span><h3 class="section">4.3 Calling the Array Example</h3>
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| 64 |
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| 65 | <p>To call the function <code>avg_of_double</code> requires making an
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| 66 | array and then passing it as an argument. Here is an example.
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| 67 | </p>
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| 68 | <div class="example">
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| 69 | <pre class="example">{
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| 70 | /* <span class="roman">The array of values to average.</span> */
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| 71 | double nums_to_average[5];
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| 72 | /* <span class="roman">The average, once we compute it.</span> */
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| 73 | double average;
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| 74 |
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| 75 | /* <span class="roman">Fill in elements of <code>nums_to_average</code>.</span> */
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| 76 |
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| 77 | nums_to_average[0] = 58.7;
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| 78 | nums_to_average[1] = 5.1;
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| 79 | nums_to_average[2] = 7.7;
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| 80 | nums_to_average[3] = 105.2;
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| 81 | nums_to_average[4] = -3.14159;
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| 82 |
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| 83 | average = avg_of_double (5, nums_to_average);
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| 84 |
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| 85 | /* <span class="roman">…now make use of <code>average</code>…</span> */
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| 86 | }
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| 87 | </pre></div>
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| 88 |
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| 89 | <p>This shows an array subscripting expression again, this time
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| 90 | on the left side of an assignment, storing a value into an
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| 91 | element of an array.
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| 92 | </p>
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| 93 | <p>It also shows how to declare a local variable that is an array:
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| 94 | <code>double nums_to_average[5];</code>. Since this declaration allocates the
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| 95 | space for the array, it needs to know the array’s length. You can
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| 96 | specify the length with any expression whose value is an integer, but
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| 97 | in this declaration the length is a constant, the integer 5.
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| 98 | </p>
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| 99 | <p>The name of the array, when used by itself as an expression, stands
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| 100 | for the address of the array’s data, and that’s what gets passed to
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| 101 | the function <code>avg_of_double</code> in <code>avg_of_double (5,
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| 102 | nums_to_average)</code>.
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| 103 | </p>
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| 104 | <p>We can make the code easier to maintain by avoiding the need to write
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| 105 | 5, the array length, when calling <code>avg_of_double</code>. That way, if
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| 106 | we change the array to include more elements, we won’t have to change
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| 107 | that call. One way to do this is with the <code>sizeof</code> operator:
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| 108 | </p>
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| 109 | <div class="example">
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| 110 | <pre class="example"> average = avg_of_double ((sizeof (nums_to_average)
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| 111 | / sizeof (nums_to_average[0])),
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| 112 | nums_to_average);
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| 113 | </pre></div>
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| 114 |
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| 115 | <p>This computes the number of elements in <code>nums_to_average</code> by dividing
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| 116 | its total size by the size of one element. See <a href="Type-Size.html">Type Size</a>, for more
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| 117 | details of using <code>sizeof</code>.
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| 118 | </p>
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| 119 | <p>We don’t show in this example what happens after storing the result of
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| 120 | <code>avg_of_double</code> in the variable <code>average</code>. Presumably
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| 121 | more code would follow that uses that result somehow. (Why compute
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| 122 | the average and not use it?) But that isn’t part of this topic.
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| 123 | </p>
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| 124 | <hr>
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| 125 | <div class="header">
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| 126 | <p>
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| 127 | Next: <a href="Array-Example-Variations.html" accesskey="n" rel="next">Array Example Variations</a>, Previous: <a href="Array-Example.html" accesskey="p" rel="prev">Array Example</a>, Up: <a href="Beyond-Integers.html" accesskey="u" rel="up">Beyond Integers</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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| 128 | </div>
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| 129 |
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| 130 |
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| 131 |
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| 132 | </body>
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