pxt-calliope/docs/reference/basic/forever.md
Sam El-Husseini e3975e65e5 pxt-microbit Accessibility PR ()
* Accessibility changes
2017-09-07 13:42:08 -07:00

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Markdown

# Forever
Keep running part of a program
[in the background](/reference/control/in-background).
```sig
basic.forever(() => {
})
```
## Example: compass
The following example constantly checks the
[compass heading](/reference/input/compass-heading)
and updates the screen with the direction.
```blocks
basic.forever(() => {
let heading = input.compassHeading()
if (heading < 45) {
basic.showString("N")
} else if (heading < 135) {
basic.showString("E")
}
else if (heading < 225) {
basic.showString("S")
}
else {
basic.showString("W")
}
})
```
## Example: counter
The following example keeps showing the [number](/types/number) stored in a global variable.
When you press button `A`, the number gets bigger.
You can use a program like this to count things with your @boardname@.
```blocks
let num = 0
basic.forever(() => {
basic.showNumber(num)
})
input.onButtonPressed(Button.A, () => {
num = num + 1
})
```
## Competing for the LED screen
If different parts of a program are each trying
to show something on the LED screen at the same time,
you may get unexpected results.
Try this on your @boardname@:
```blocks
basic.forever(() => {
basic.showNumber(6789)
})
input.onButtonPressed(Button.A, () => {
basic.showNumber(2)
})
```
## See also
[while](/blocks/loops/while), [on button pressed](/reference/input/on-button-pressed), [in background](/reference/control/in-background)