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<h1 class="title">Loops</h1>
<p><small>There is a new edition of the book and this is an old link.</small></p>
<blockquote>
<p>Rust has three kinds of loops: <code>loop</code>, <code>while</code>, and <code>for</code>.
The <code>loop</code> keyword tells Rust to execute a block of code over and over again forever or until you explicitly tell it to stop.
<code>while</code> loops evaluate a block of code until a condition ceases to be true.
A <code>for</code> loop executes some code for each item in a collection.</p>
</blockquote>
<pre class="rust rust-example-rendered">
<span class="kw">loop</span> {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"again!"</span>);
}
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">number</span> <span class="op">=</span> <span class="number">3</span>;
<span class="kw">while</span> <span class="ident">number</span> <span class="op">!=</span> <span class="number">0</span> {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"{}!"</span>, <span class="ident">number</span>);
<span class="ident">number</span> <span class="op">=</span> <span class="ident">number</span> <span class="op">-</span> <span class="number">1</span>;
}
<span class="kw">let</span> <span class="ident">a</span> <span class="op">=</span> [<span class="number">10</span>, <span class="number">20</span>, <span class="number">30</span>, <span class="number">40</span>, <span class="number">50</span>];
<span class="kw">for</span> <span class="ident">element</span> <span class="kw">in</span> <span class="ident">a</span>.<span class="ident">iter</span>() {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"the value is: {}"</span>, <span class="ident">element</span>);
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Aloop%20%7B%0A%20%20%20%20println!(%22again!%22)%3B%0A%7D%0A%0Alet%20mut%20number%20%3D%203%3B%0Awhile%20number%20!%3D%200%20%7B%0A%20%20%20%20println!(%22%7B%7D!%22%2C%20number)%3B%0A%20%20%20%20number%20%3D%20number%20-%201%3B%0A%7D%0A%0Alet%20a%20%3D%20%5B10%2C%2020%2C%2030%2C%2040%2C%2050%5D%3B%0Afor%20element%20in%20a.iter()%20%7B%0A%20%20%20%20println!(%22the%20value%20is%3A%20%7B%7D%22%2C%20element)%3B%0A%7D%0A%7D">Run</a></pre>
<hr />
<p>Here are the relevant sections in the new and old books:</p>
<ul>
<li><strong><a href="second-edition/ch03-05-control-flow.html#repetition-with-loops">In the second edition: Ch 3.05 — Control flow</a></strong></li>
<li><small><a href="first-edition/loops.html">In the first edition: Ch 3.6 — Loops</a></small></li>
</ul>
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