feat(main): 添加复合类型、函数和控制流示例

- 在ex2_scalar_types中添加布尔类型变量
- 在ex3_compound_types中添加数组遍历示例
- 实现ex4_functions中的数学运算函数（加法、阶乘、奇偶判断）
- 添加ex5_control_flow中的条件判断和fizzbuzz逻辑
- 实现ex6_loops中的各种循环结构（loop、while、for）
- 添加mini_guessing_game猜数字小游戏
- 实现count_letters字母统计功能
- 注释掉部分练习函数，启用新的练习内容

part2/src/main.rs

@@ -8,7 +8,12 @@ fn main() {
     println!("Hello, world!");
     // ex1_variables();
     // ex2_scalar_types();
-    ex3_compound_types();
+    // ex3_compound_types();
+    // ex4_functions();
+    // ex5_control_flow();
+    // ex6_loops();
+    mini_guessing_game();
+    // ex8_stats();
 }
 
 // ============================================================
@@ -52,6 +57,7 @@ fn ex2_scalar_types() {
     let u8_var: u8 = 42;
     let i32_var: i32 = 128;
     let f64_var: f64 = 3.14;
+    let bool_var: bool = true;
     let char_var = '2';
 
     println!("u8 as i32: {}", u8_var as i32);
@@ -83,6 +89,12 @@ fn ex3_compound_types() {
     let b1 = tup.1;
     let c1 = tup.2;
     println!("tup: {}, {}, {}", a1, b1, c1);
+    let arr: [i32; 5] = [1, 2, 3, 4, 5];
+    for i in 0..arr.len() {
+        println!("arr[{}]: {}", i, arr[i]);
+    }
+    println!("arr length: {}", arr.len());
+    // arr[10]; error: index out of bounds: the len is 5 but the index is 10
 }
 
 // ============================================================
@@ -95,29 +107,35 @@ fn ex3_compound_types() {
 // 4. 写一个无返回值的函数 greet(name: &str)，打印 "你好，{name}！"。
 #[allow(dead_code)]
 fn add(a: i32, b: i32) -> i32 {
-    // TODO
-    0
+    a + b
 }
 
 #[allow(dead_code)]
 fn factorial(n: u32) -> u32 {
-    // TODO
-    0
+    let mut result = 1;
+    for i in 1..=n {
+        result *= i;
+    }
+    result
 }
 
 #[allow(dead_code)]
 fn is_even(n: i32) -> bool {
-    // TODO
-    false
+    n % 2 == 0
 }
 
 #[allow(dead_code)]
 fn greet(name: &str) {
     // TODO
+    println!("你好，{}！", name)
 }
 
 fn ex4_functions() {
     // 在这里调用上面四个函数进行测试
+    println!("add(1, 2): {}", add(1, 2));
+    println!("factorial(5): {}", factorial(5));
+    println!("is_even(5): {}", is_even(5));
+    greet("Rust");
 }
 
 // ============================================================
@@ -132,17 +150,43 @@ fn ex4_functions() {
 //    根据一个 bool 变量给另一个变量赋不同的值。
 #[allow(dead_code)]
 fn grade(score: u32) -> &'static str {
-    // TODO
-    "F"
+    let mut x = "";
+    if score >= 90 && score <= 100 {
+        x = "A";
+    } else if score >= 80 && score < 90 {
+        x = "B";
+    } else if score >= 70 && score < 80 {
+        x = "C";
+    } else if score >= 60 && score < 70 {
+        x = "D";
+    } else {
+        x = "F";
+    };
+    return x;
 }
 
 #[allow(dead_code)]
 fn fizzbuzz(n: u32) {
-    // TODO
+    for i in (1..=n) {
+        if i % 3 == 0 && i % 5 == 0 {
+            println!("FizzBuzz")
+        } else if i % 3 == 0 {
+            println!("Fizz")
+        } else if i % 5 == 0 {
+            println!("Buzz")
+        } else {
+            println!("{}", i)
+        }
+    }
 }
 
 fn ex5_control_flow() {
     // 在这里测试
+    let score = 89;
+    let condition = true;
+    let n = if condition { 100 } else { 50 };
+    println!("grade：{}", grade(score));
+    fizzbuzz(n);
 }
 
 // ============================================================
@@ -157,6 +201,31 @@ fn ex5_control_flow() {
 #[allow(dead_code)]
 fn ex6_loops() {
     // TODO: 在这里写你的代码
+    let mut sum = 0;
+    let mut i = 1;
+    let result = loop {
+        sum += i;
+        if i == 100 {
+            break sum;
+        };
+        i += 1;
+    };
+    println!("sum: {}", result);
+
+    let mut i = 10;
+    while i > 0 {
+        println!("倒数: {}", i);
+        i -= 1;
+    }
+
+    let arr = [10, 20, 30, 40, 50];
+    for (i, item) in arr.iter().enumerate() {
+        println!("index: {}, value: {}", i, item);
+    }
+
+    for i in 1..=5 {
+        println!("{} 的平方是 {}", i, i * i);
+    }
 }
 
 // ============================================================
@@ -173,6 +242,19 @@ fn ex6_loops() {
 #[allow(dead_code)]
 fn mini_guessing_game() {
     // TODO: 在这里写你的代码
+    let secret_number = 62;
+    let guesses: [i32; 5] = [10, 50, 35, 60, 42];
+
+    for (i, guess) in guesses.iter().enumerate() {
+        if guess < &secret_number {
+            println!("第{}次猜测，{} 太小了！", i + 1, guess);
+        } else if guess > &secret_number {
+            println!("第{}次猜测，{} 太大了！", i + 1, guess);
+        } else {
+            println!("第{}次猜测，{} 猜对了！", i + 1, guess);
+            break;
+        };
+    }
 }
 
 // ============================================================
@@ -186,9 +268,21 @@ fn mini_guessing_game() {
 #[allow(dead_code)]
 fn count_letters(s: &str) -> (u32, u32) {
     // TODO
-    (0, 0)
+    let chars = s.chars();
+    let tup: (u32, u32) = (0, 0);
+    let (mut upper, mut lower) = tup;
+    for c in chars {
+        if c.is_uppercase() {
+            upper += 1;
+        } else if c.is_lowercase() {
+            lower += 1;
+        }
+    }
+    (upper, lower)
 }
 
 fn ex8_stats() {
     // 在这里测试 count_letters
+    let (upper, lower) = count_letters("Hello, World!");
+    println!("大写字母数量：{}，小写字母数量：{}", upper, lower);
 }

part3/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "part3"
+version = "0.1.0"