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| 22 | <title>Array Example (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="Beyond-Integers.html" rel="up" title="Beyond Integers">
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| 33 | <link href="Array-Example-Call.html" rel="next" title="Array Example Call">
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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"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Array-Example-Call.html" accesskey="n" rel="next">Array Example Call</a>, Previous: <a href="Float-Example.html" accesskey="p" rel="prev">Float 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="An-Example-with-Arrays"></span><h3 class="section">4.2 An Example with Arrays</h3>
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| 64 | <span id="index-array-example"></span>
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| 65 |
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| 66 | <p>A function to take the average of three numbers is very specific and
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| 67 | limited. A more general function would take the average of any number
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| 68 | of numbers. That requires passing the numbers in an array. An array
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| 69 | is an object in memory that contains a series of values of the same
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| 70 | data type. This chapter presents the basic concepts and use of arrays
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| 71 | through an example; for the full explanation, see <a href="Arrays.html">Arrays</a>.
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| 72 | </p>
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| 73 | <p>Here’s a function definition to take the average of several
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| 74 | floating-point numbers, passed as type <code>double</code>. The first
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| 75 | parameter, <code>length</code>, specifies how many numbers are passed. The
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| 76 | second parameter, <code>input_data</code>, is an array that holds those
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| 77 | numbers.
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| 78 | </p>
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| 79 | <div class="example">
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| 80 | <pre class="example">double
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| 81 | avg_of_double (int length, double input_data[])
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| 82 | {
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| 83 | double sum = 0;
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| 84 | int i;
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| 85 |
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| 86 | for (i = 0; i < length; i++)
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| 87 | sum = sum + input_data[i];
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| 88 |
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| 89 | return sum / length;
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| 90 | }
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| 91 | </pre></div>
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| 92 |
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| 93 | <p>This introduces the expression to refer to an element of an array:
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| 94 | <code>input_data[i]</code> means the element at index <code>i</code> in
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| 95 | <code>input_data</code>. The index of the element can be any expression
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| 96 | with an integer value; in this case, the expression is <code>i</code>.
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| 97 | See <a href="Accessing-Array-Elements.html">Accessing Array Elements</a>.
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| 98 | </p>
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| 99 | <span id="index-zero_002dorigin-indexing"></span>
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| 100 | <p>The lowest valid index in an array is 0, <em>not</em> 1, and the highest
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| 101 | valid index is one less than the number of elements. (This is known
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| 102 | as <em>zero-origin indexing</em>.)
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| 103 | </p>
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| 104 | <p>This example also introduces the way to declare that a function
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| 105 | parameter is an array. Such declarations are modeled after the syntax
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| 106 | for an element of the array. Just as <code>double foo</code> declares that
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| 107 | <code>foo</code> is of type <code>double</code>, <code>double input_data[]</code>
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| 108 | declares that each element of <code>input_data</code> is of type
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| 109 | <code>double</code>. Therefore, <code>input_data</code> itself has type “array
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| 110 | of <code>double</code>.”
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| 111 | </p>
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| 112 | <p>When declaring an array parameter, it’s not necessary to say how long
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| 113 | the array is. In this case, the parameter <code>input_data</code> has no
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| 114 | length information. That’s why the function needs another parameter,
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| 115 | <code>length</code>, for the caller to provide that information to the
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| 116 | function <code>avg_of_double</code>.
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| 117 | </p>
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| 118 | <hr>
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| 119 | <div class="header">
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| 120 | <p>
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| 121 | Next: <a href="Array-Example-Call.html" accesskey="n" rel="next">Array Example Call</a>, Previous: <a href="Float-Example.html" accesskey="p" rel="prev">Float 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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| 122 | </div>
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| 123 |
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| 124 |
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