123 lines
3.2 KiB
Markdown
123 lines
3.2 KiB
Markdown
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# Boolean
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true or false.
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### @parent js/language
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A Boolean has one of two possible values: `true`; `false`. Boolean (logical) operators (*and*, *or*, *not*) take Boolean inputs and yields a Boolean value. Comparison operators on other types ([numbers](/microbit/reference/types/number), [strings](/microbit/reference/types/string)) yields a Boolean value.
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### Block Editor
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In the Block Editor, the following blocks represent the true and false Boolean values, which can be plugged in anywhere a Boolean value is expected:
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The next three blocks represent the three Boolean (logic) operators:
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The next six blocks represent comparison operators that yield a Boolean value. Most comparisons you will do involve [numbers](/microbit/reference/types/number):
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### Touch Develop
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### ~hide
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```
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let condition = true
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let condition2 = true
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```
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### ~
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Boolean values and operators are often used with an [if](/microbit/reference/logic/if) or [while](/microbit/js/while) statement to determine which code will execute next. For example:
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```
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if (condition && condition2) {
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// This code runs if both `condition` and `condition2` are `true`
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} else {
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// This code runs if either `condition` or `condition2` is `false`
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}
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```
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### Functions that return a Boolean
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Some functions return a Boolean value, which you can store in a Boolean variable. For example, the following code gets the on/off state of `point (1, 2)` and stores this in the Boolean variable named `on`. Then the code clears the screen if `on` is `true`:
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```
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let on = led.point(1, 2)
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if (on) {
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basic.clearScreen()
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}
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```
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### Boolean operators
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Boolean operators take Boolean inputs and evaluate to a Boolean output:
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### Conjunction: `A and B`
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`A and B` evaluates to `true` if-and-only-if both A and B are true:
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- `false and false` = `false`
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- `false and true` = `false`
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- `true and false` = `false`
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- `true and true` = `true`
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### Disjunction: `A or B`
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`A or B` evaluates to `true` if-and-only-if either A is true or B is true:
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- `false or false` = `false`
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- `false or true` = `true`
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- `true or false` = `true`
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- `true or true` = `true`
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### Negation: `not A`
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`not A` evaluates to the opposite (negation) of A:
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* `not false` = `true`
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* `not true` = `false`
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### Example
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This example turns on LED `3 , 3`, if LEDs `1 , 1` and `2 , 2` are both on:
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```
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if (led.point(1, 1) && led.point(2, 2)) {
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led.plot(3, 3)
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}
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```
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### Comparisons of numbers and strings
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When you compare two Numbers, you get a Boolean value, such as the comparison `x < 5` in the code below:
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```
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let x = Math.random(10)
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if (x < 5) {
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basic.showString("Low", 150)
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} else {
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basic.showString("High", 150)
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}
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```
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See the documentation on [Numbers](/microbit/reference/types/number) for more information on comparing two Numbers. You can also [compare strings](/microbit/reference/types/string-functions) using the `equals` function.
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### Lessons
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[rotation animation](/microbit/lessons/rotation-animation), [digi yoyo](/microbit/lessons/digi-yoyo), [love meter](/microbit/lessons/love-meter), [zoomer](/microbit/lessons/zoomer)
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### See also
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[if](/microbit/reference/logic/if), [while](/microbit/js/while), [number](/microbit/reference/types/number)
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