add control_flow

data/1.rust初阶/2.rust基本概念/10.控制流/control_flow.md

 # 控制流
 
+Rust 语言的逻辑控制流有： 
+- if/else 条件分支
+- loop 循环
+- while 循环
+- for in range 循环
+- match 表达式
+- if let
+- while let
+
+代码表示分别为：
+
+```rust
+
+if condition_a {}
+else if condition_b {}
+else {}
+
+loop {}
+
+'outer: loop {
+    'innter: loop {
+        ...
+        break;
+        // or
+        break 'outer;
+    }
+}
+
+loop {
+    ...
+    break counter * 2;
+}
+
+while condition_a {}
+
+for n in 1..=100 {}
+
+for name in names.iter() {}
+
+match val {
+    tuple_a => statement_a ;
+    tuple_b => statement_b ;
+    (x, y) if x = y => statement_c ;
+    (x, y) => statement_d ;
+    (Enum::A, Enum::B) => statement_e ;
+    (n @ 1..=50, m @ 51..=100) => statement_f ;
+    (Some(n), Some(m)) => statement_g ;
+}
+
+if let Some(i) = number {}
+while let Some(i) = number {}
+
+```
+
+下列代码能正常运行的是：
+
+## 答案
+
+```rust
+
+fn main() {
+    let mut count = 0;
+    'outer: loop {
+        'inner: loop {
+            if count >= 20 {
+                break 'outer; 
+            }
+            count += 2;
+        }
+    }
+
+    println!("Complete!");
+}
+
+```
+
+
+## 选项
+
+###
+
+```rust
+
+fn main() {
+    let mut count = 0;
+    'outer: loop {
+        'inner: loop {
+            if count <= 20 {
+                count += 2;
+                goto: 'inner; 
+            }
+        }
+    }
+
+    println!("Complete!");
+}
+
+```
+
+
+### 
+
+```rust
+
+fn main() {
+    for i in 0..=10 {
+        if i == 10 {
+            panic!("This never gonna happy");
+        }
+    }
+}
+
+```
+
+###
+
+```rust
+
+fn main() {
+    let guess = 51;
+    let secret_number = 42;
+    let result = if guess < secret_number {
+        "Too small"
+    } else if guess > secret_number {
+        "Too big"
+    } else {
+        42
+    };
+    
+    println!("{}", result);
+}
+
+```
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