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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" class="active"><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"><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 &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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<h2 id="display-and-debug"><a class="header" href="#display-and-debug">Display and debug</a></h2>
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<p><strong><a href="https://youtu.be/jd3pC248c0o">See this chapter on YouTube</a></strong></p>
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<p>Simple variables in Rust can be printed with <code>{}</code> inside <code>println!</code>. But some variables can't, and you need to <strong>debug print</strong>. Debug print is printing for the programmer, because it usually shows more information. Debug sometimes doesn't look pretty, because it has extra information to help you.</p>
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<p>How do you know if you need <code>{:?}</code> and not <code>{}</code>? The compiler will tell you. For example:</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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let doesnt_print = ();
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println!("This will not print: {}", doesnt_print); // ⚠️
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}
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</code></pre></pre>
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<p>When we run this, the compiler says:</p>
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<pre><code class="language-text">error[E0277]: `()` doesn't implement `std::fmt::Display`
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--> src\main.rs:3:41
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3 | println!("This will not print: {}", doesnt_print);
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| ^^^^^^^^^^^^ `()` cannot be formatted with the default formatter
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= help: the trait `std::fmt::Display` is not implemented for `()`
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= note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
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= note: required by `std::fmt::Display::fmt`
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= note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
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</code></pre>
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<p>This is a lot of information. But the important part is: <code>you may be able to use {:?} (or {:#?} for pretty-print) instead</code>. This means that you can try <code>{:?}</code>, and also <code>{:#?}</code> <code>{:#?}</code> is called "pretty printing". It is like <code>{:?}</code> but prints with different formatting over more lines.</p>
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<p>So Display means printing with <code>{}</code>, and Debug means printing with <code>{:?}</code>.</p>
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<p>One more thing: you can also use <code>print!</code> without <code>ln</code> if you don't want a new line.</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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print!("This will not print a new line");
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println!(" so this will be on the same line");
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}
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</code></pre></pre>
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<p>This prints <code>This will not print a new line so this will be on the same line</code>.</p>
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<h3 id="smallest-and-largest-numbers"><a class="header" href="#smallest-and-largest-numbers">Smallest and largest numbers</a></h3>
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<p>If you want to see the smallest and biggest numbers, you can use MIN and MAX after the name of the type:</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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println!("The smallest i8 is {} and the biggest i8 is {}.", i8::MIN, i8::MAX); // hint: printing std::i8::MIN means "print MIN inside of the i8 section in the standard library"
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println!("The smallest u8 is {} and the biggest u8 is {}.", u8::MIN, u8::MAX);
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println!("The smallest i16 is {} and the biggest i16 is {}.", i16::MIN, i16::MAX);
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println!("The smallest u16 is {} and the biggest u16 is {}.", u16::MIN, u16::MAX);
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println!("The smallest i32 is {} and the biggest i32 is {}.", i32::MIN, i32::MAX);
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println!("The smallest u32 is {} and the biggest u32 is {}.", u32::MIN, u32::MAX);
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println!("The smallest i64 is {} and the biggest i64 is {}.", i64::MIN, i64::MAX);
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println!("The smallest u64 is {} and the biggest u64 is {}.", u64::MIN, u64::MAX);
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println!("The smallest i128 is {} and the biggest i128 is {}.", i128::MIN, i128::MAX);
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println!("The smallest u128 is {} and the biggest u128 is {}.", u128::MIN, u128::MAX);
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}
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</code></pre></pre>
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<p>This will print:</p>
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<pre><code class="language-text">The smallest i8 is -128 and the biggest i8 is 127.
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The smallest u8 is 0 and the biggest u8 is 255.
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The smallest i16 is -32768 and the biggest i16 is 32767.
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The smallest u16 is 0 and the biggest u16 is 65535.
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The smallest i32 is -2147483648 and the biggest i32 is 2147483647.
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The smallest u32 is 0 and the biggest u32 is 4294967295.
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The smallest i64 is -9223372036854775808 and the biggest i64 is 9223372036854775807.
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The smallest u64 is 0 and the biggest u64 is 18446744073709551615.
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The smallest i128 is -170141183460469231731687303715884105728 and the biggest i128 is 170141183460469231731687303715884105727.
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The smallest u128 is 0 and the biggest u128 is 340282366920938463463374607431768211455.
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</code></pre>
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