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<div class="example" id="arrays">
<h2><a href="./">Go by Example</a>: Arrays</h2>
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<p>In Go, an <em>array</em> is a numbered sequence of elements of a
specific length.</p>
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<a href="http://play.golang.org/p/l-A8eBnwio"><img title="Run code" src="play.png" class="run" /></a>
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>
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<div class="highlight"><pre><span class="kn">import</span> <span class="s">&quot;fmt&quot;</span>
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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
</pre></div>
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<p>Here we create an array <code>a</code> that will hold exactly
5 <code>int</code>s. The type of elements and length are both
part of the array&rsquo;s type. By default an array is
zero-valued, which for <code>int</code>s means <code>0</code>s.</p>
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<div class="highlight"><pre> <span class="kd">var</span> <span class="nx">a</span> <span class="p">[</span><span class="mi">5</span><span class="p">]</span><span class="kt">int</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;emp:&quot;</span><span class="p">,</span> <span class="nx">a</span><span class="p">)</span>
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<p>We can set a value at an index using the
<code>array[index] = value</code> syntax, and get a value with
<code>array[index]</code>.</p>
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<div class="highlight"><pre> <span class="nx">a</span><span class="p">[</span><span class="mi">4</span><span class="p">]</span> <span class="p">=</span> <span class="mi">100</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;set:&quot;</span><span class="p">,</span> <span class="nx">a</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;get:&quot;</span><span class="p">,</span> <span class="nx">a</span><span class="p">[</span><span class="mi">4</span><span class="p">])</span>
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<p>The builtin <code>len</code> returns the length of an array.</p>
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<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;len:&quot;</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="nx">a</span><span class="p">))</span>
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<p>Use this syntax to declare and initialize an array
in one line.</p>
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<div class="highlight"><pre> <span class="nx">b</span> <span class="o">:=</span> <span class="p">[</span><span class="mi">5</span><span class="p">]</span><span class="kt">int</span><span class="p">{</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">}</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;dcl:&quot;</span><span class="p">,</span> <span class="nx">b</span><span class="p">)</span>
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<p>Array types are one-dimensional, but you can
compose types to build multi-dimensional data
structures.</p>
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<div class="highlight"><pre> <span class="kd">var</span> <span class="nx">twoD</span> <span class="p">[</span><span class="mi">2</span><span class="p">][</span><span class="mi">3</span><span class="p">]</span><span class="kt">int</span>
<span class="k">for</span> <span class="nx">i</span> <span class="o">:=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">i</span> <span class="p">&lt;</span> <span class="mi">2</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span> <span class="p">{</span>
<span class="k">for</span> <span class="nx">j</span> <span class="o">:=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">j</span> <span class="p">&lt;</span> <span class="mi">3</span><span class="p">;</span> <span class="nx">j</span><span class="o">++</span> <span class="p">{</span>
<span class="nx">twoD</span><span class="p">[</span><span class="nx">i</span><span class="p">][</span><span class="nx">j</span><span class="p">]</span> <span class="p">=</span> <span class="nx">i</span> <span class="o">+</span> <span class="nx">j</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;2d: &quot;</span><span class="p">,</span> <span class="nx">twoD</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
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<p>Note that arrays appear in the form <code>[v1 v2 v3 ...]</code>
when printed with <code>fmt.Println</code>.</p>
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<div class="highlight"><pre><span class="gp">$</span> go run arrays.go
<span class="go">emp: [0 0 0 0 0]</span>
<span class="go">set: [0 0 0 0 100]</span>
<span class="go">get: 100</span>
<span class="go">len: 5</span>
<span class="go">dcl: [1 2 3 4 5]</span>
<span class="go">2d: [[0 1 2] [1 2 3]]</span>
</pre></div>
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<p>You&rsquo;ll see <em>slices</em> much more often than arrays in
typical Go. We&rsquo;ll look at slices next.</p>
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<p class="next">
Next example: <a href="slices">Slices</a>.
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<p class="footer">
by <a href="https://twitter.com/mmcgrana">@mmcgrana</a> | <a href="mailto:mmcgrana@gmail.com">feedback</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/arrays">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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