> 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/branch.md).

# 分支结构（if / switch）

### if 语句

```cpp
if (条件) {
    // 条件为真时执行
}
```

### if-else

```cpp
if (score >= 60)
    cout << "及格";
else
    cout << "不及格";
```

### 多分支 if-else if-else

```cpp
if (score >= 90)      cout << "A";
else if (score >= 80) cout << "B";
else if (score >= 60) cout << "C";
else                  cout << "D";
```

### switch 语句

用于判断某个表达式的多个**等值**情况：

```cpp
switch (op) {
    case '+': cout << a + b; break;
    case '-': cout << a - b; break;
    case '*': cout << a * b; break;
    default:  cout << "未知运算符";
}
```

要点：

* 每个 case 结束一般要 `break`，否则会**贯穿**执行下一个 case。
* switch 的判断表达式只能是整型或字符型，不能是区间。

### 常见错误

* 把 `==` 写成 `=`
* `if` 后面多加 `;`，导致分支体为空
* 条件写反，如把 `>` 写成 `<`


---

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