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<h1 id="附录-c表达式"><a class="header" href="#附录-c表达式">附录 C：表达式</a></h1>
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<p>在<a href="https://course.rs/basic/base-type/statement-expression.html">语句与表达式</a>章节中，我们对表达式有过介绍，下面对这些常用表达式进行一一说明。</p>
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<h3 id="基本表达式"><a class="header" href="#基本表达式">基本表达式</a></h3>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>let n = 3;
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let s = "test";
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<span class="boring">}</span></code></pre></pre>
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<h3 id="if-表达式"><a class="header" href="#if-表达式">if 表达式</a></h3>
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<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
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let var1 = 10;
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let var2 = if var1 >= 10 {
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var1
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} else {
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var1 + 10
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};
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println!("{}", var2);
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}</code></pre></pre>
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<p>通过 <code>if</code> 表达式将值赋予 <code>var2</code>。</p>
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<p>你还可以在循环中结合 <code>continue</code> 、<code>break</code> 来使用：</p>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>let mut v = 0;
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for i in 1..10 {
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v = if i == 9 {
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continue
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} else {
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i
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}
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}
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println!("{}", v);
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<span class="boring">}</span></code></pre></pre>
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<h3 id="if-let-表达式"><a class="header" href="#if-let-表达式">if let 表达式</a></h3>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>let o = Some(3);
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let v = if let Some(x) = o {
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x
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} else {
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0
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};
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<span class="boring">}</span></code></pre></pre>
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<h3 id="match-表达式"><a class="header" href="#match-表达式">match 表达式</a></h3>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>let o = Some(3);
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let v = match o {
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Some(x) => x,
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_ => 0
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};
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<span class="boring">}</span></code></pre></pre>
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<h3 id="loop-表达式"><a class="header" href="#loop-表达式">loop 表达式</a></h3>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>let mut n = 0;
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let v = loop {
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if n == 10 {
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break n
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}
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n += 1;
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};
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<span class="boring">}</span></code></pre></pre>
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<h3 id="语句块"><a class="header" href="#语句块">语句块</a></h3>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>let mut n = 0;
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let v = {
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println!("before: {}", n);
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n += 1;
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println!("after: {}", n);
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n
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};
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println!("{}", v);
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<span class="boring">}</span></code></pre></pre>
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