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<ol class="chapter"><li class="chapter-item expanded "><a href="Chapter_0.html"><strong aria-hidden="true">1.</strong> Updates</a></li><li class="chapter-item expanded "><a href="Chapter_1.html"><strong aria-hidden="true">2.</strong> Introduction</a></li><li class="chapter-item expanded "><a href="Chapter_2.html"><strong aria-hidden="true">3.</strong> Who am I?</a></li><li class="chapter-item expanded "><a href="Chapter_3.html"><strong aria-hidden="true">4.</strong> Writing Rust in Easy English</a></li><li class="chapter-item expanded "><a href="Chapter_4.html"><strong aria-hidden="true">5.</strong> Rust Playground</a></li><li class="chapter-item expanded "><a href="Chapter_5.html"><strong aria-hidden="true">6.</strong> 🚧 and ⚠️</a></li><li class="chapter-item expanded "><a href="Chapter_6.html"><strong aria-hidden="true">7.</strong> Comments</a></li><li class="chapter-item expanded "><a href="Chapter_7.html"><strong aria-hidden="true">8.</strong> Types</a></li><li class="chapter-item expanded "><a href="Chapter_8.html"><strong aria-hidden="true">9.</strong> Type inference</a></li><li class="chapter-item expanded "><a href="Chapter_9.html"><strong aria-hidden="true">10.</strong> Printing 'hello, world!'</a></li><li class="chapter-item expanded "><a href="Chapter_10.html"><strong aria-hidden="true">11.</strong> Display and debug</a></li><li class="chapter-item expanded "><a href="Chapter_11.html"><strong aria-hidden="true">12.</strong> Mutability (changing)</a></li><li class="chapter-item expanded "><a href="Chapter_12.html"><strong aria-hidden="true">13.</strong> The stack, the heap, and pointers</a></li><li class="chapter-item expanded "><a href="Chapter_13.html"><strong aria-hidden="true">14.</strong> More about printing</a></li><li class="chapter-item expanded "><a href="Chapter_14.html"><strong aria-hidden="true">15.</strong> Strings</a></li><li class="chapter-item expanded "><a href="Chapter_15.html"><strong aria-hidden="true">16.</strong> const and static</a></li><li class="chapter-item expanded "><a href="Chapter_16.html"><strong aria-hidden="true">17.</strong> More on references</a></li><li class="chapter-item expanded "><a href="Chapter_17.html"><strong aria-hidden="true">18.</strong> Mutable references</a></li><li class="chapter-item expanded "><a href="Chapter_18.html"><strong aria-hidden="true">19.</strong> Giving references to functions</a></li><li class="chapter-item expanded "><a href="Chapter_19.html"><strong aria-hidden="true">20.</strong> Copy types</a></li><li class="chapter-item expanded "><a href="Chapter_20.html"><strong aria-hidden="true">21.</strong> Collection types</a></li><li class="chapter-item expanded "><a href="Chapter_21.html"><strong aria-hidden="true">22.</strong> Vectors</a></li><li class="chapter-item expanded "><a href="Chapter_22.html"><strong aria-hidden="true">23.</strong> Tuples</a></li><li class="chapter-item expanded "><a href="Chapter_23.html"><strong aria-hidden="true">24.</strong> Control flow</a></li><li class="chapter-item expanded "><a href="Chapter_24.html"><strong aria-hidden="true">25.</strong> Structs</a></li><li class="chapter-item expanded "><a href="Chapter_25.html"><strong aria-hidden="true">26.</strong> Enums</a></li><li class="chapter-item expanded "><a href="Chapter_26.html" class="active"><strong aria-hidden="true">27.</strong> Loops</a></li><li class="chapter-item expanded "><a href="Chapter_27.html"><strong aria-hidden="true">28.</strong> Implementing structs and enums</a></li><li class="chapter-item expanded "><a href="Chapter_28.html"><strong aria-hidden="true">29.</strong> Destructuring</a></li><li class="chapter-item expanded "><a href="Chapter_29.html"><strong aria-hidden="true">30.</strong> References and the dot operator</a></li><li class="chapter-item expanded "><a href="Chapter_30.html"><strong aria-hidden="true">31.</strong> Generics</a></li><li class="chapter-item expanded "><a href="Chapter_31.html"><strong aria-hidden="true">32.</strong> Option and Result</a></li><li class="chapter-item expanded "><a href="Chapter_32.html"><strong aria-hidden="true">33.</strong> Other collections</a></li><li class="chapter-item expanded "><a href="Chapter_33.html"><strong aria-hidden="true">34.</strong> The ? operator</a></li><li class="chapter-item expanded "><a href="Chapter_34.html"><strong aria-hidden="true">35.</strong> Traits</a></li><li class="chapter-item expanded "><a href="Chapter_35.html"><strong aria-hidden="true">36.</strong> Chaining methods</a></li><li class="chapter-item expanded "><a href="Chapter_36.html"><strong aria-hidden="true">37.</strong> Iterators</a></li><li class="chapter-item expanded "><a href="Chapter_37.html"><strong aria-hidden="true">38.</strong> Closures</a></li><li class="chapter-item expanded "><a href="Chapter_38.html"><strong aria-hidden="true">39.</strong> The dbg! macro and .inspect</a></li><li class="chapter-item expanded "><a href="Chapter_39.html"><strong aria-hidden="true">40.</strong> Types of &amp;str</a></li><li class="chapter-item expanded "><a href="Chapter_40.html"><strong aria-hidden="true">41.</strong> Lifetimes</a></li><li class="chapter-item expanded "><a href="Chapter_41.html"><strong aria-hidden="true">42.</strong> Interior mutability</a></li><li class="chapter-item expanded "><a href="Chapter_42.html"><strong aria-hidden="true">43.</strong> Cow</a></li><li class="chapter-item expanded "><a href="Chapter_43.html"><strong aria-hidden="true">44.</strong> Type aliases</a></li><li class="chapter-item expanded "><a href="Chapter_44.html"><strong aria-hidden="true">45.</strong> The todo! macro</a></li><li class="chapter-item expanded "><a href="Chapter_45.html"><strong aria-hidden="true">46.</strong> Rc</a></li><li class="chapter-item expanded "><a href="Chapter_46.html"><strong aria-hidden="true">47.</strong> Multiple threads</a></li><li class="chapter-item expanded "><a href="Chapter_47.html"><strong aria-hidden="true">48.</strong> Closures in functions</a></li><li class="chapter-item expanded "><a href="Chapter_48.html"><strong aria-hidden="true">49.</strong> impl Trait</a></li><li class="chapter-item expanded "><a href="Chapter_49.html"><strong aria-hidden="true">50.</strong> Arc</a></li><li class="chapter-item expanded "><a href="Chapter_50.html"><strong aria-hidden="true">51.</strong> Channels</a></li><li class="chapter-item expanded "><a href="Chapter_51.html"><strong aria-hidden="true">52.</strong> Reading Rust documentation</a></li><li class="chapter-item expanded "><a href="Chapter_52.html"><strong aria-hidden="true">53.</strong> Attributes</a></li><li class="chapter-item expanded "><a href="Chapter_53.html"><strong aria-hidden="true">54.</strong> Box</a></li><li class="chapter-item expanded "><a href="Chapter_54.html"><strong aria-hidden="true">55.</strong> Box around traits</a></li><li class="chapter-item expanded "><a href="Chapter_55.html"><strong aria-hidden="true">56.</strong> Default and the builder pattern</a></li><li class="chapter-item expanded "><a href="Chapter_56.html"><strong aria-hidden="true">57.</strong> Deref and DerefMut</a></li><li class="chapter-item expanded "><a href="Chapter_57.html"><strong aria-hidden="true">58.</strong> Crates and modules</a></li><li class="chapter-item expanded "><a href="Chapter_58.html"><strong aria-hidden="true">59.</strong> Testing</a></li><li class="chapter-item expanded "><a href="Chapter_59.html"><strong aria-hidden="true">60.</strong> External crates</a></li><li class="chapter-item expanded "><a href="Chapter_60.html"><strong aria-hidden="true">61.</strong> A tour of the standard library</a></li><li class="chapter-item expanded "><a href="Chapter_61.html"><strong aria-hidden="true">62.</strong> Writing macros</a></li><li class="chapter-item expanded "><a href="Chapter_62.html"><strong aria-hidden="true">63.</strong> cargo</a></li><li class="chapter-item expanded "><a href="Chapter_63.html"><strong aria-hidden="true">64.</strong> Taking user input</a></li><li class="chapter-item expanded "><a href="Chapter_64.html"><strong aria-hidden="true">65.</strong> Using files</a></li><li class="chapter-item expanded "><a href="Chapter_65.html"><strong aria-hidden="true">66.</strong> cargo doc</a></li><li class="chapter-item expanded "><a href="Chapter_66.html"><strong aria-hidden="true">67.</strong> The end?</a></li></ol>
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<h1 class="menu-title">Easy Rust</h1>
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<main>
<h2 id="loops"><a class="header" href="#loops">Loops</a></h2>
<p>With loops you can tell Rust to continue something until you want it to stop. You use <code>loop</code> to start a loop that does not stop, unless you tell it when to <code>break</code>.</p>
<pre><pre class="playground"><code class="language-rust">fn main() { // This program will never stop
loop {
}
}
</code></pre></pre>
<p>So let's tell the compiler when it can break.</p>
<pre><pre class="playground"><code class="language-rust">fn main() {
let mut counter = 0; // set a counter to 0
loop {
counter +=1; // increase the counter by 1
println!(&quot;The counter is now: {}&quot;, counter);
if counter == 5 { // stop when counter == 5
break;
}
}
}
</code></pre></pre>
<p>This will print:</p>
<pre><code class="language-text">The counter is now: 1
The counter is now: 2
The counter is now: 3
The counter is now: 4
The counter is now: 5
</code></pre>
<p>If you have a loop inside of a loop, you can give them names. With names, you can tell Rust which loop to <code>break</code> out of. Use <code>'</code> (called a &quot;tick&quot;) and a <code>:</code> to give it a name:</p>
<pre><pre class="playground"><code class="language-rust">fn main() {
let mut counter = 0;
let mut counter2 = 0;
println!(&quot;Now entering the first loop.&quot;);
'first_loop: loop {
// Give the first loop a name
counter += 1;
println!(&quot;The counter is now: {}&quot;, counter);
if counter &gt; 9 {
// Starts a second loop inside this loop
println!(&quot;Now entering the second loop.&quot;);
'second_loop: loop {
// now we are inside 'second_loop
println!(&quot;The second counter is now: {}&quot;, counter2);
counter2 += 1;
if counter2 == 3 {
break 'first_loop; // Break out of 'first_loop so we can exit the program
}
}
}
}
}
</code></pre></pre>
<p>This will print:</p>
<pre><code class="language-text">Now entering the first loop.
The counter is now: 1
The counter is now: 2
The counter is now: 3
The counter is now: 4
The counter is now: 5
The counter is now: 6
The counter is now: 7
The counter is now: 8
The counter is now: 9
The counter is now: 10
Now entering the second loop.
The second counter is now: 0
The second counter is now: 1
The second counter is now: 2
</code></pre>
<p>A <code>while</code> loop is a loop that continues while something is still <code>true</code>. Each loop, Rust will check if it is still <code>true</code>. If it becomes <code>false</code>, Rust will stop the loop.</p>
<pre><pre class="playground"><code class="language-rust">fn main() {
let mut counter = 0;
while counter &lt; 5 {
counter +=1;
println!(&quot;The counter is now: {}&quot;, counter);
}
}
</code></pre></pre>
<p>A <code>for</code> loop lets you tell Rust what to do each time. But in a <code>for</code> loop, the loop stops after a certain number of times. <code>for</code> loops use <strong>ranges</strong> very often. You use <code>..</code> and <code>..=</code> to create a range.</p>
<ul>
<li><code>..</code> creates an <strong>exclusive</strong> range: <code>0..3</code> creates <code>0, 1, 2</code>.</li>
<li><code>..=</code> creates an <strong>inclusive</strong> range: <code>0..=3</code> = <code>0, 1, 2, 3</code>.</li>
</ul>
<pre><pre class="playground"><code class="language-rust">fn main() {
for number in 0..3 {
println!(&quot;The number is: {}&quot;, number);
}
for number in 0..=3 {
println!(&quot;The next number is: {}&quot;, number);
}
}
</code></pre></pre>
<p>This prints:</p>
<pre><code class="language-text">The number is: 0
The number is: 1
The number is: 2
The next number is: 0
The next number is: 1
The next number is: 2
The next number is: 3
</code></pre>
<p>Also notice that <code>number</code> becomes the variable name for 0..3. We could have called it <code>n</code>, or <code>ntod_het___hno_f</code>, or anything. We can then use that name in <code>println!</code>.</p>
<p>If you don't need a variable name, use <code>_</code>.</p>
<pre><pre class="playground"><code class="language-rust">fn main() {
for _ in 0..3 {
println!(&quot;Printing the same thing three times&quot;);
}
}
</code></pre></pre>
<p>This prints:</p>
<pre><code class="language-text">Printing the same thing three times
Printing the same thing three times
Printing the same thing three times
</code></pre>
<p>because we didn't give it any number to print each time.</p>
<p>And actually, if you give a variable name and don't use it, Rust will tell you:</p>
<pre><pre class="playground"><code class="language-rust">fn main() {
for number in 0..3 {
println!(&quot;Printing the same thing three times&quot;);
}
}
</code></pre></pre>
<p>This prints the same thing as above. The program compiles fine, but Rust will remind you that you didn't use <code>number</code>:</p>
<pre><code class="language-text">warning: unused variable: `number`
--&gt; src\main.rs:2:9
|
2 | for number in 0..3 {
| ^^^^^^ help: if this is intentional, prefix it with an underscore: `_number`
</code></pre>
<p>Rust suggests writing <code>_number</code> instead of <code>_</code>. Putting <code>_</code> in front of a variable name means &quot;maybe I will use it later&quot;. But using just <code>_</code> means &quot;I don't care about this variable at all&quot;. So you can put <code>_</code> in front of variable names if you will use them later and don't want the compiler to tell you about them.</p>
<p>You can also use <code>break</code> to return a value. You write the value right after <code>break</code> and use a <code>;</code>. Here is an example with a <code>loop</code> and a break that gives <code>my_number</code> its value.</p>
<pre><pre class="playground"><code class="language-rust">fn main() {
let mut counter = 5;
let my_number = loop {
counter +=1;
if counter % 53 == 3 {
break counter;
}
};
println!(&quot;{}&quot;, my_number);
}
</code></pre></pre>
<p>This prints <code>56</code>. <code>break counter;</code> means &quot;break and return the value of counter&quot;. And because the whole block starts with <code>let</code>, <code>my_number</code> gets the value.</p>
<p>Now that we know how to use loops, here is a better solution to our <code>match</code> problem with colours from before. It is a better solution because we want to compare everything, and a <code>for</code> loop looks at every item.</p>
<pre><pre class="playground"><code class="language-rust">fn match_colours(rbg: (i32, i32, i32)) {
println!(&quot;Comparing a colour with {} red, {} blue, and {} green:&quot;, rbg.0, rbg.1, rbg.2);
let new_vec = vec![(rbg.0, &quot;red&quot;), (rbg.1, &quot;blue&quot;), (rbg.2, &quot;green&quot;)]; // Put the colours in a vec. Inside are tuples with the colour names
let mut all_have_at_least_10 = true; // Start with true. We will set it to false if one colour is less than 10
for item in new_vec {
if item.0 &lt; 10 {
all_have_at_least_10 = false; // Now it's false
println!(&quot;Not much {}.&quot;, item.1) // And we print the colour name.
}
}
if all_have_at_least_10 { // Check if it's still true, and print if true
println!(&quot;Each colour has at least 10.&quot;)
}
println!(); // Add one more line
}
fn main() {
let first = (200, 0, 0);
let second = (50, 50, 50);
let third = (200, 50, 0);
match_colours(first);
match_colours(second);
match_colours(third);
}
</code></pre></pre>
<p>This prints:</p>
<pre><code class="language-text">Comparing a colour with 200 red, 0 blue, and 0 green:
Not much blue.
Not much green.
Comparing a colour with 50 red, 50 blue, and 50 green:
Each colour has at least 10.
Comparing a colour with 200 red, 50 blue, and 0 green:
Not much green.
</code></pre>
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