245 lines
4.4 KiB
Markdown
245 lines
4.4 KiB
Markdown
# 流程控制
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### if/else
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1. 🌟
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```rust,editable
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// 填空
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fn main() {
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let n = 5;
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if n < 0 {
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println!("{} is negative", n);
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} __ n > 0 {
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println!("{} is positive", n);
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} __ {
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println!("{} is zero", n);
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}
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}
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```
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2. 🌟🌟 if/else 可以用作表达式来进行赋值
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```rust,editable
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// 修复错误
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fn main() {
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let n = 5;
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let big_n =
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if n < 10 && n > -10 {
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println!(" 数字太小，先增加 10 倍再说");
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10 * n
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} else {
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println!("数字太大，我们得让它减半");
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n / 2.0 ;
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}
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println!("{} -> {}", n, big_n);
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}
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```
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### for
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3. 🌟 `for in` 可以用于迭代一个迭代器，例如序列 `a..b`.
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```rust,editable
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fn main() {
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for n in 1..=100 { // 修改此行，让代码工作
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if n == 100 {
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panic!("NEVER LET THIS RUN")
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}
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}
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}
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```
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4. 🌟🌟
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```rust,editable
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// 修复错误，不要新增或删除代码行
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fn main() {
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let names = [String::from("liming"),String::from("hanmeimei")];
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for name in names {
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// do something with name...
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}
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println!("{:?}", names);
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let numbers = [1, 2, 3];
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// numbers中的元素实现了 Copy，因此无需转移所有权
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for n in numbers {
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// do something with name...
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}
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println!("{:?}", numbers);
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}
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```
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5. 🌟
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```rust,editable
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fn main() {
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let a = [4,3,2,1];
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// 通过索引和值的方式迭代数组 `a`
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for (i,v) in a.__ {
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println!("第{}个元素是{}",i+1,v);
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}
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}
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```
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### while
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6. 🌟🌟 当条件为 true 时，`while` 将一直循环
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```rust,editable
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// 填空，让最后一行的 println! 工作 !
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fn main() {
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// 一个计数值
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let mut n = 1;
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// 当条件为真时，不停的循环
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while n __ 10 {
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if n % 15 == 0 {
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println!("fizzbuzz");
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} else if n % 3 == 0 {
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println!("fizz");
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} else if n % 5 == 0 {
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println!("buzz");
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} else {
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println!("{}", n);
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}
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__;
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}
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println!("n 的值是 {}, 循环结束",n);
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}
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```
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### continue and break
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7. 🌟 使用 `break` 可以跳出循环
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```rust,editable
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// 填空，不要修改其它代码
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fn main() {
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let mut n = 0;
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for i in 0..=100 {
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if n == 66 {
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__
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}
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n += 1;
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}
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assert_eq!(n, 66);
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}
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```
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8. 🌟🌟 `continue` 会结束当次循环并立即开始下一次循环
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```rust,editable
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// 填空，不要修改其它代码
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fn main() {
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let mut n = 0;
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for i in 0..=100 {
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if n != 66 {
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n+=1;
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__;
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}
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__
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}
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assert_eq!(n, 66);
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}
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```
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### loop
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9. 🌟🌟 loop 一般都需要配合 `break` 或 `continue` 一起使用。
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```rust,editable
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// 填空，不要修改其它代码
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fn main() {
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let mut count = 0u32;
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println!("Let's count until infinity!");
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// 无限循环
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loop {
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count += 1;
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if count == 3 {
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println!("three");
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// 跳过当此循环的剩余代码
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__;
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}
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println!("{}", count);
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if count == 5 {
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println!("OK, that's enough");
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__;
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}
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}
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assert_eq!(count, 5);
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}
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```
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10. 🌟🌟 loop 是一个表达式，因此我们可以配合 `break` 来返回一个值
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```rust,editable
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// 填空
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fn main() {
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let mut counter = 0;
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let result = loop {
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counter += 1;
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if counter == 10 {
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__;
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}
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};
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assert_eq!(result, 20);
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}
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```
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11. 🌟🌟🌟 当有多层循环时，你可以使用 `continue` 或 `break` 来控制外层的循环。要实现这一点，外部的循环必须拥有一个标签 `'label`, 然后在 `break` 或 `continue` 时指定该标签
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```rust,editable
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// 填空
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fn main() {
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let mut count = 0;
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'outer: loop {
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'inner1: loop {
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if count >= 20 {
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// 这只会跳出 inner1 循环
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break 'inner1; // 这里使用 `break` 也是一样的
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}
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count += 2;
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}
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count += 5;
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'inner2: loop {
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if count >= 30 {
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break 'outer;
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}
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continue 'outer;
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}
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}
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assert!(count == __)
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}
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```
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> 你可以在[这里](https://github.com/sunface/rust-by-practice/blob/master/solutions/flow-control.md)找到答案(在 solutions 路径下) |