# analogRead

## 函数原型

```cpp
int analogRead(uint8_t pin);
```

## 作用

读取指定引脚的电位，**只有支持模拟输入的引脚才能调用此函数。**

**注意：** 在调用此函数之前要保证该引脚已经 `pinMode` 过，且为输入模式。

## 参数

* `pin`

  指定引脚的编号，如： `10` , `A0` 等。

## 返回值

* `int` 整型

  指定的引脚的电位

返回值的范围为 **0\~1023**

## 示例

```cpp
// 假设 4 号引脚连接的是 3V
int state = digitalWrite(4);
// state = 3 * 1023 / 5;
```


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