> 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/loop.md).

# 循环结构（for / while / do-while）

### for 循环

适合**已知次数**的循环：

```cpp
for (int i = 1; i <= 5; i++) {
    cout << i << " ";
}
```

三段式：`for (初始化; 条件; 步进)`。

### while 循环

适合**条件控制**的循环：

```cpp
int n = 123, cnt = 0;
while (n > 0) {
    n /= 10;
    cnt++;
}
cout << cnt << endl;  // 3
```

### do-while 循环

**至少执行一次**，条件在后：

```cpp
int x;
do {
    cin >> x;
} while (x < 0);  // 反复输入直到 x 非负
```

### break 与 continue

* `break`：立即跳出整个循环
* `continue`：跳过本次循环剩余部分，进入下一次

```cpp
for (int i = 1; i <= 10; i++) {
    if (i == 5) continue;  // 跳过 5
    if (i == 8) break;     // 到 8 停止
    cout << i << " ";      // 输出 1 2 3 4 6 7
}
```

### 死循环

`while (true) { ... }` 配合 `break` 使用，可做“不确定次数”的循环。


---

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