> 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/basics/io.md).

# 输入输出语句

### cout / cin

```cpp
#include <iostream>
using namespace std;

int main() {
    int a, b;
    cin >> a >> b;
    cout << a + b << endl;
    return 0;
}
```

* `>>` 是**提取运算符**，`<<` 是**插入运算符**。
* `endl` 表示换行并刷新缓冲区，也可用 `"\n"`。

### scanf / printf（C 风格）

速度更快，格式更精细，需要 `#include <cstdio>`。

```cpp
#include <cstdio>

int main() {
    int a; double x;
    scanf("%d%lf", &a, &x);
    printf("%d %.2f\n", a, x);
    return 0;
}
```

常用格式符：

| 类型             | 格式符          |
| -------------- | ------------ |
| int            | `%d`         |
| long long      | `%lld`       |
| float / double | `%f` / `%lf` |
| char           | `%c`         |
| 字符串            | `%s`         |

### 格式控制

* `%.2f`：保留两位小数
* `%5d`：宽度为 5，右对齐
* `%05d`：宽度 5，不足补 0

### 注意

* `.2f` 只做**四舍五入显示**，原值不变。
* scanf 中变量要加取地址符 `&`（字符串数组除外）。


---

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