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constants
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: Constants</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'variables';
}
if (e.key == "ArrowRight") {
window.location.href = 'for';
}
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<body>
<div class="example" id="constants">
<h2><a href="./">Go by Example</a>: Constants</h2>
<table>
<tr>
<td class="docs">
<p>Go supports <em>constants</em> of character, string, boolean,
and numeric values.</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="http://play.golang.org/p/Vw-pXSfo9_b"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kn">import</span> <span class="p">(</span>
<span class="s">"fmt"</span>
<span class="s">"math"</span>
<span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p><code>const</code> declares a constant value.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">const</span> <span class="nx">s</span> <span class="kt">string</span> <span class="p">=</span> <span class="s">"constant"</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">s</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>A <code>const</code> statement can appear anywhere a <code>var</code>
statement can.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">const</span> <span class="nx">n</span> <span class="p">=</span> <span class="mi">500000000</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Constant expressions perform arithmetic with
arbitrary precision.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">const</span> <span class="nx">d</span> <span class="p">=</span> <span class="mf">3e20</span> <span class="o">/</span> <span class="nx">n</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">d</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>A numeric constant has no type until it’s given
one, such as by an explicit conversion.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nb">int64</span><span class="p">(</span><span class="nx">d</span><span class="p">))</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>A number can be given a type by using it in a
context that requires one, such as a variable
assignment or function call. For example, here
<code>math.Sin</code> expects a <code>float64</code>.</p>
</td>
<td class="code">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">math</span><span class="p">.</span><span class="nf">Sin</span><span class="p">(</span><span class="nx">n</span><span class="p">))</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code">
<pre class="chroma"><span class="gp">$</span> go run constant.go
<span class="go">constant
</span><span class="go">6e+11
</span><span class="go">600000000000
</span><span class="go">-0.28470407323754404</span></pre>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="for">For</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>
</div>
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