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2.1.28, initiation update to PXT v5.28.24 (#54)

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Amerlander
2019-12-02 05:58:26 +01:00
committed by Peli de Halleux
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docs/blocks/logic/boolean.md
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# Boolean
true or false.
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](/reference/types/number), [strings](/reference/types/string) yields a Boolean value.
The following blocks represent the true and false Boolean values, which can be plugged in anywhere a Boolean value is expected:
```blocks
true;
false;
```
The next three blocks represent the three Boolean (logic) operators:
```blocks
true && false;
true || false;
!true;
```
The next six blocks represent comparison operators that yield a Boolean value. Most comparisons you will do involve [numbers](/reference/types/number):
```blocks
42 == 0;
42 != 0;
42 < 0;
42 > 0;
42 <= 0;
42 >= 0;
```
Boolean values and operators are often used with an [if](/blocks/logic/if) or [while](/blocks/loops/while) statement to determine which code will execute next. For example:
### 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`:
### 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:
```blocks
false && false == false;
false && true == false;
true && false == false;
true && true == true;
```
### Disjunction: `A or B`
`A or B` evaluates to `true` if-and-only-if either A is true or B is true:
```blocks
false || false == false;
false || true == true;
true || false == true;
true || true == true;
```
### Negation: `not A`
`not A` evaluates to the opposite (negation) of A:
```blocks
!false == true;
!true == false;
```
### Example
This example turns on LED `3 , 3`, if LEDs `1 , 1` and `2 , 2` are both on:
```blocks
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:
```blocks
let x = Math.random(5)
if(x < 5) {
basic.showString("low");
} else {
basic.showString("high");
}
```
See the documentation on [Numbers](/reference/types/number) for more information on comparing two Numbers. You can also [compare strings](/reference/types/string-functions) using the `equals` function.
### See also
[if](/blocks/logic/if), [while](/blocks/loops/while), [number](/reference/types/number)

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docs/blocks/logic/if.md
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# If
### @parent blocks/language
Conditionally run code depending on whether a [Boolean](/blocks/logic/boolean) condition is true or false.
```blocks
if(true) {
}
```
Click on the dark blue gear icon (see above) to add an *else* or *if* to the current block.
### Example: adjusting screen brightness
```blocks
if(input.lightLevel()<100){
led.setBrightness(255);
}
```
If the [light level](/reference/input/light-level) is `< 100`, this code sets the brightness to `255`:
### See also
[while loop](/blocks/loops/while), [for](/blocks/loops/for), [boolean](/blocks/logic/boolean)