> For the complete documentation index, see [llms.txt](https://docs.1l.lol/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.1l.lol/functions/return-and-params.md).

# 函数返回与传参

### 函数的定义与调用

函数把一段可复用的逻辑封装起来。

```cpp
int add(int a, int b) {   // 返回类型 函数名(形参列表)
    return a + b;
}

int main() {
    cout << add(3, 5);    // 调用，实参 3、5
    return 0;
}
```

### 声明与定义分离

函数可以先声明（原型），后定义：

```cpp
int add(int a, int b);   // 声明
// ... main 中使用 ...
int add(int a, int b) { return a + b; }  // 定义
```

### 形参 vs 实参

* **形参**：函数定义中的参数，是局部变量
* **实参**：调用时传入的具体值

### 返回值

* `return` 返回一个值并结束函数
* 无返回值用 `void`
* 函数只能返回一个值，需要多个结果时用引用 / 指针参数带回

```cpp
void minmax(int a[], int n, int &mn, int &mx) {
    mn = mx = a[0];
    for (int i = 1; i < n; i++) {
        if (a[i] < mn) mn = a[i];
        if (a[i] > mx) mx = a[i];
    }
}
```

### 递归函数

函数调用自身，必须有**终止条件**：

```cpp
int fact(int n) {
    if (n <= 1) return 1;      // 终止条件
    return n * fact(n - 1);    // 递归
}
```

### 默认参数与重载（了解）

```cpp
int add(int a, int b = 10) { return a + b; }   // 默认参数
int add(int a, int b, int c) { return a+b+c; } // 函数重载（同名不同参数）
```

> 相关：变量作用域、函数参数传递（值 / 引用 / 指针）。


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