> 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/case.md).

# 大小写

### 判断大小写

```cpp
char ch;
cin >> ch;
if (ch >= 'A' && ch <= 'Z') cout << "大写";
else if (ch >= 'a' && ch <= 'z') cout << "小写";
else if (ch >= '0' && ch <= '9') cout << "数字";
```

### 转换

利用大小写字母 ASCII 相差 32：

```cpp
char c = 'g';
cout << (char)(c - 32);   // G，小写转大写
cout << (char)('G' + 32);  // g，大写转小写
```

### 用库函数（）

```cpp
#include <cctype>
char c = 'a';
toupper(c);   // 转大写
tolower(c);   // 转小写
isupper(c);   // 是否大写
islower(c);   // 是否小写
isalpha(c);   // 是否字母
isdigit(c);   // 是否数字
```

### 统计整串里的字母

```cpp
string s = "AbC";
int up = 0;
for (char c : s)
    if (isupper(c)) up++;
cout << up;   // 2
```


---

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