75 lines
1.9 KiB
Markdown
75 lines
1.9 KiB
Markdown
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# While
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Repeat code in a loop while a condition is true. #docs #while #language
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### @parent js/language
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Repeat code while a [Boolean](/microbit/reference/types/boolean) `condition` is true.
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### ~hide
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```
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let condition = false
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```
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### ~
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### Block Editor
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### Touch Develop
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```
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while (condition) {
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// This code runs if `condition` is `true`
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}
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```
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The while loop has a *condition* that evaluates to a [Boolean](/microbit/reference/types/boolean) value. After the `do` keyword, add the code that you want to run while the `condition` is `true`. The while loop concludes with `end while`.
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The condition is tested before any code runs. Which means that if the condition is false, the code inside the loop doesn't execute. Use the [break statement](/microbit/js/break) to exit a while loop before it's complete.
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### Example: diagonal line
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The following example uses a while loop to make a diagonal line on the LED screen (points `0, 0`, `1, 1`, `2, 2`, `3, 3`, `4, 4`).
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// index is set to 4
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```
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let index = 4
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while (index >= 0) {
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led.plot(index, index)
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// // subtract 1 from `index` each time through loop
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index = index - 1
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}
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```
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### Example: count until A button pressed
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The following example shows numbers on the screen(0, 1, 2, 3...), until the "A" button is pressed.
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```
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let x = 0
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while (true) {
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basic.showNumber(x, 100)
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let pressed = input.buttonIsPressed("A")
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if (pressed) {
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break
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} else {
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x = x + 1
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}
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basic.pause(1000)
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}
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```
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### Lessons
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[rotation animation](/microbit/lessons/rotation-animation), [digi yoyo](/microbit/lessons/digi-yoyo)
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### See also
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[on button pressed](/microbit/reference/input/on-button-pressed), [for](/microbit/reference/loops/for), [if](/microbit/reference/logic/if), [break](/microbit/js/break), [forever](/microbit/reference/basic/forever), [in background](/microbit/reference/control/in-background)
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