> 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/computer-basics/ascii.md).

# ASCII 编码

### 什么是 ASCII

ASCII（美国信息交换标准代码）用 7 位二进制（0\~127）表示 128 个常用字符，是字符与数字之间的对应表。

### 必记的 ASCII 值

| 字符         | 十进制       |
| ---------- | --------- |
| 空格         | 32        |
| '0' \~ '9' | 48 \~ 57  |
| 'A' \~ 'Z' | 65 \~ 90  |
| 'a' \~ 'z' | 97 \~ 122 |

记忆技巧：`'A' = 65`，大小写相差 32（`'a' = 'A' + 32`）；数字字符与数值相差 48。

### 字符与 ASCII 的转换

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

int main() {
    char c = 'A';
    cout << (int)c << endl;   // 65，字符转 ASCII
    cout << (char)97 << endl; // a，ASCII 转字符

    // 大小写转换
    char lower = 'g';
    cout << char(lower - 32) << endl; // G
    cout << char('G' + 32) << endl;   // g

    // 数字字符转数字
    char d = '7';
    int x = d - '0';  // 7
    cout << x << endl;
    return 0;
}
```


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