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arrays
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arrays
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<!DOCTYPE html>
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<title>Go by Example: Arrays</title>
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<div class="example" id="arrays">
<h2><a href="./">Go by Example</a>: Arrays</h2>
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<td class="docs">
<p>In Go, an <em>array</em> is a numbered sequence of elements of a
specific length. In typical Go code, <a href="slices">slices</a> are
much more common; arrays are useful in some special
scenarios.</p>
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<td class="docs">
</td>
<td class="code leading">
<a href="https://go.dev/play/p/zVIFeNnUdwv"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<pre class="chroma"><code><span class="line"><span class="cl"><span class="kn">package</span> <span class="nx">main</span></span></span></code></pre>
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<td class="docs">
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<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"><span class="kn">import</span> <span class="s">"fmt"</span></span></span></code></pre>
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<td class="docs">
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<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span></span></span></code></pre>
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<td class="docs">
<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’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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<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"> <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></span><span class="line"><span class="cl"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"emp:"</span><span class="p">,</span> <span class="nx">a</span><span class="p">)</span></span></span></code></pre>
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<td class="docs">
<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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<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"> <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></span><span class="line"><span class="cl"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"set:"</span><span class="p">,</span> <span class="nx">a</span><span class="p">)</span>
</span></span><span class="line"><span class="cl"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"get:"</span><span class="p">,</span> <span class="nx">a</span><span class="p">[</span><span class="mi">4</span><span class="p">])</span></span></span></code></pre>
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<td class="docs">
<p>The builtin <code>len</code> returns the length of an array.</p>
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<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"len:"</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="nx">a</span><span class="p">))</span></span></span></code></pre>
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<td class="docs">
<p>Use this syntax to declare and initialize an array
in one line.</p>
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<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"> <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></span><span class="line"><span class="cl"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"dcl:"</span><span class="p">,</span> <span class="nx">b</span><span class="p">)</span></span></span></code></pre>
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<td class="docs">
<p>You can also have the compiler count the number of
elements for you with <code>...</code></p>
</td>
<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"> <span class="nx">b</span> <span class="p">=</span> <span class="p">[</span><span class="o">...</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></span><span class="line"><span class="cl"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"dcl:"</span><span class="p">,</span> <span class="nx">b</span><span class="p">)</span></span></span></code></pre>
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<td class="docs">
<p>If you specify the index with <code>:</code>, the elements in
between will be zeroed.</p>
</td>
<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"> <span class="nx">b</span> <span class="p">=</span> <span class="p">[</span><span class="o">...</span><span class="p">]</span><span class="kt">int</span><span class="p">{</span><span class="mi">100</span><span class="p">,</span> <span class="mi">3</span><span class="p">:</span> <span class="mi">400</span><span class="p">,</span> <span class="mi">500</span><span class="p">}</span>
</span></span><span class="line"><span class="cl"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"idx:"</span><span class="p">,</span> <span class="nx">b</span><span class="p">)</span></span></span></code></pre>
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<td class="docs">
<p>Array types are one-dimensional, but you can
compose types to build multi-dimensional data
structures.</p>
</td>
<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"> <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></span><span class="line"><span class="cl"> <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"><</span> <span class="mi">2</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl"> <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"><</span> <span class="mi">3</span><span class="p">;</span> <span class="nx">j</span><span class="o">++</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl"> <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></span><span class="line"><span class="cl"> <span class="p">}</span>
</span></span><span class="line"><span class="cl"> <span class="p">}</span>
</span></span><span class="line"><span class="cl"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"2d: "</span><span class="p">,</span> <span class="nx">twoD</span><span class="p">)</span></span></span></code></pre>
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<td class="docs">
<p>You can create and initialize multi-dimensional
arrays at once too.</p>
</td>
<td class="code">
<pre class="chroma"><code><span class="line"><span class="cl"> <span class="nx">twoD</span> <span class="p">=</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="p">{</span>
</span></span><span class="line"><span class="cl"> <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></span><span class="line"><span class="cl"> <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></span><span class="line"><span class="cl"> <span class="p">}</span>
</span></span><span class="line"><span class="cl"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"2d: "</span><span class="p">,</span> <span class="nx">twoD</span><span class="p">)</span>
</span></span><span class="line"><span class="cl"><span class="p">}</span></span></span></code></pre>
</td>
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</table>
<table>
<tr>
<td class="docs">
<p>Note that arrays appear in the form <code>[v1 v2 v3 ...]</code>
when printed with <code>fmt.Println</code>.</p>
</td>
<td class="code">
<pre class="chroma"><code><span class="line"><span class="cl"><span class="gp">$</span> go run arrays.go
</span></span><span class="line"><span class="cl"><span class="go">emp: [0 0 0 0 0]
</span></span></span><span class="line"><span class="cl"><span class="go">set: [0 0 0 0 100]
</span></span></span><span class="line"><span class="cl"><span class="go">get: 100
</span></span></span><span class="line"><span class="cl"><span class="go">len: 5
</span></span></span><span class="line"><span class="cl"><span class="go">dcl: [1 2 3 4 5]
</span></span></span><span class="line"><span class="cl"><span class="go">dcl: [1 2 3 4 5]
</span></span></span><span class="line"><span class="cl"><span class="go">idx: [100 0 0 400 500]
</span></span></span><span class="line"><span class="cl"><span class="go">2d: [[0 1 2] [1 2 3]]
</span></span></span><span class="line"><span class="cl"><span class="go">2d: [[1 2 3] [1 2 3]]</span></span></span></code></pre>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="slices">Slices</a>.
</p>
<p class="footer">
by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> and <a href="https://eli.thegreenplace.net">Eli Bendersky</a> | <a href="https://github.com/mmcgrana/gobyexample">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
</p>
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