pxt-calliope/docs/reference/basic/forever.md
2016-06-11 22:28:57 -04:00

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# 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", 100)
} else if (heading < 135) {
basic.showString("E", 100)
}
else if (heading < 225) {
basic.showString("S", 100)
}
else {
basic.showString("W", 100)
}
})
```
### Example: counter
The following example keeps showing the [number](/reference/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 BBC micro:bit.
```blocks
let num = 0
basic.forever(() => {
basic.showNumber(num, 150)
})
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 micro:bit:
```blocks
basic.forever(() => {
basic.showNumber(6789, 150)
})
input.onButtonPressed(Button.A, () => {
basic.showNumber(2, 150)
})
```
### See also
[while](/reference/loops/while), [on button pressed](/reference/input/on-button-pressed), [in background](/reference/control/in-background)