pxt-calliope/docs/reference/js/boolean.md

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2016-03-26 00:47:20 +01:00
# Boolean
true or false.
### @parent js/language
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.
### Block Editor
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:
![](/static/mb/boolean-0.png)
The next three blocks represent the three Boolean (logic) operators:
![](/static/mb/boolean-1.png)
The next six blocks represent comparison operators that yield a Boolean value. Most comparisons you will do involve [numbers](/microbit/reference/types/number):
![](/static/mb/boolean-2.png)
### Touch Develop
### ~hide
```
let condition = true
let condition2 = true
```
### ~
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:
```
if (condition && condition2) {
// This code runs if both `condition` and `condition2` are `true`
} else {
// This code runs if either `condition` or `condition2` is `false`
}
```
### Functions that return a Boolean
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`:
```
let on = led.point(1, 2)
if (on) {
basic.clearScreen()
}
```
### Boolean operators
Boolean operators take Boolean inputs and evaluate to a Boolean output:
### Conjunction: `A and B`
`A and B` evaluates to `true` if-and-only-if both A and B are true:
- `false and false` = `false`
- `false and true` = `false`
- `true and false` = `false`
- `true and true` = `true`
### Disjunction: `A or B`
`A or B` evaluates to `true` if-and-only-if either A is true or B is true:
- `false or false` = `false`
- `false or true` = `true`
- `true or false` = `true`
- `true or true` = `true`
### Negation: `not A`
`not A` evaluates to the opposite (negation) of A:
* `not false` = `true`
* `not true` = `false`
### Example
This example turns on LED `3 , 3`, if LEDs `1 , 1` and `2 , 2` are both on:
```
if (led.point(1, 1) && led.point(2, 2)) {
led.plot(3, 3)
}
```
### Comparisons of numbers and strings
When you compare two Numbers, you get a Boolean value, such as the comparison `x < 5` in the code below:
```
let x = Math.random(10)
if (x < 5) {
basic.showString("Low", 150)
} else {
basic.showString("High", 150)
}
```
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.
### Lessons
[rotation animation](/microbit/lessons/rotation-animation), [digi yoyo](/microbit/lessons/digi-yoyo), [love meter](/microbit/lessons/love-meter), [zoomer](/microbit/lessons/zoomer)
### See also
[if](/microbit/reference/logic/if), [while](/microbit/js/while), [number](/microbit/reference/types/number)