> 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/data-structures/array-1d.md).

# 一维数组

### 定义与使用

数组是一组**相同类型**变量的集合，用下标访问。

```cpp
int a[10];              // 10 个元素，下标 0~9
int b[5] = {1, 2, 3};   // 前 3 个赋值，其余为 0
int c[] = {1, 2, 3};    // 自动确定长度 3

for (int i = 0; i < 5; i++) cin >> b[i];   // 输入
for (int i = 0; i < 5; i++) cout << b[i];  // 输出
```

### 重要性质

* 下标从 **0** 开始，`a[n]` 会越界，属于未定义行为。
* 数组长度一旦定义不可改变（变长数组不在考纲内）。
* 全局数组默认全 0；局部数组不会自动清零，建议手动初始化。

### 常用操作

```cpp
int a[100], n = 5;
int sum = 0, mx = a[0];
for (int i = 0; i < n; i++) { sum += a[i]; if (a[i] > mx) mx = a[i]; }

// 逆序
for (int i = 0, j = n - 1; i < j; i++, j--) swap(a[i], a[j]);

// 查找最大值下标
int pos = 0;
for (int i = 1; i < n; i++) if (a[i] > a[pos]) pos = i;
```

### 数组开多大

一般按题目数据范围 +5 开，例如 `n ≤ 100` 就开 `a[105]`。注意不要开得过小导致越界。


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