# map()

[Math]

## 描述

Re-maps a number from one range to another. That is, a value of `fromLow` would get mapped to `toLow`, a value of `fromHigh` to `toHigh`, values in-between to values in-between, etc.

Does not constrain values to within the range, because out-of-range values are sometimes intended and useful. The `constrain()` function may be used either before or after this function, if limits to the ranges are desired.

Note that the “lower bounds” of either range may be larger or smaller than the “upper bounds” so the `map()` function may be used to reverse a range of numbers, for example

`y = map(x, 1, 50, 50, 1);`

The function also handles negative numbers well, so that this example

`y = map(x, 1, 50, 50, -100);`

is also valid and works well.

The `map()` function uses integer math so will not generate fractions, when the math might indicate that it should do so. Fractional remainders are truncated, and are not rounded or averaged.

## 語法

`map(value, fromLow, fromHigh, toLow, toHigh)`

## 參數

`value`: the number to map
`fromLow`: the lower bound of the value’s current range
`fromHigh`: the upper bound of the value’s current range
`toLow`: the lower bound of the value’s target range
`toHigh`: the upper bound of the value’s target range

## 回傳

The mapped value.

## Example Code

```/* Map an analog value to 8 bits (0 to 255) */
void setup() {}

void loop()
{
val = map(val, 0, 1023, 0, 255);
analogWrite(9, val);
}```

## Appendix

For the mathematically inclined, here’s the whole function

```long map(long x, long in_min, long in_max, long out_min, long out_max)
{
return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}```

## 參考

### 語法參考主頁面

86Duino 參考的文本是根據 Creative Commons Attribution-ShareAlike 3.0 License，部分文本是從 the Arduino reference 修改的。 參考中的代碼示例已發佈到公共領域。

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