2.1.28, initiation update to PXT v5.28.24 (#54)
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Amerlander
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Peli de Halleux
Peli de Halleux
parent
38a964516e
commit
5c114a0c57
@ -1,9 +0,0 @@
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# Logic
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```cards
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if(true) {}
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true;
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true && false;
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!true;
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1 != 0;
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```
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# Boolean
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true or false.
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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](/reference/types/number), [strings](/reference/types/string) yields a Boolean value.
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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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```blocks
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true;
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false;
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```
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The next three blocks represent the three Boolean (logic) operators:
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```blocks
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true && false;
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true || false;
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!true;
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```
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The next six blocks represent comparison operators that yield a Boolean value. Most comparisons you will do involve [numbers](/reference/types/number):
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```blocks
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42 == 0;
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42 != 0;
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42 < 0;
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42 > 0;
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42 <= 0;
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42 >= 0;
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```
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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:
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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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### 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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```blocks
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false && false == false;
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false && true == false;
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true && false == false;
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true && true == true;
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```
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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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```blocks
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false || false == false;
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false || true == true;
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true || false == true;
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true || true == true;
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```
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### Negation: `not A`
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`not A` evaluates to the opposite (negation) of A:
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```blocks
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!false == true;
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!true == false;
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```
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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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```blocks
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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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```blocks
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let x = Math.random(5)
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if(x < 5) {
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basic.showString("low");
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} else {
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basic.showString("high");
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}
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```
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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.
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### See also
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[if](/blocks/logic/if), [while](/blocks/loops/while), [number](/reference/types/number)
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# If
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### @parent blocks/language
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Conditionally run code depending on whether a [Boolean](/blocks/logic/boolean) condition is true or false.
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```blocks
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if(true) {
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}
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```
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Click on the dark blue gear icon (see above) to add an *else* or *if* to the current block.
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### Example: adjusting screen brightness
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```blocks
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if(input.lightLevel()<100){
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led.setBrightness(255);
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}
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```
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If the [light level](/reference/input/light-level) is `< 100`, this code sets the brightness to `255`:
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### See also
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[while loop](/blocks/loops/while), [for](/blocks/loops/for), [boolean](/blocks/logic/boolean)
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# Loops
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```cards
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for(let i = 0;i<5;i++) {}
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while(true) {}
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basic.forever(() => {});
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```
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# For
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### @parent blocks/language
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Run part of the program the number of times you say.
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### Example: Count to 4
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This program will show the numbers 0, 1, 2, 3, and 4 one after another on the LED screen.
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```blocks
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for(let i = 0; i < 5; ++i) {
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basic.showNumber(i)
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}
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```
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### See also
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[repeat](/blocks/loops/repeat), [while](/blocks/loops/while), [if](/blocks/logic/if), [show number](/reference/basic/show-number)
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# Repeat
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Run part of the program the number of times you say.
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### Block Editor
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### See also
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[for](/blocks/loops/for), [while](/blocks/loops/while), [if](/blocks/logic/if), [show number](/reference/basic/show-number)
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# While
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Repeat code while a [Boolean](/blocks/logic/boolean) `condition` is true.
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```blocks
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while(true) {
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}
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```
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The while loop has a *condition* that evaluates to a [Boolean](/blocks/logic/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.
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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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```blocks
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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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index--;
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}
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```
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### See also
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[on button pressed](/reference/input/on-button-pressed), [for](/blocks/loops/for), [if](/blocks/logic/if), [forever](/reference/basic/forever)
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# Math
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### [Numeric](/reference/types/number) values: 0, 1, 2, ...
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```block
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0;
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1;
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2;
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```
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### Arithmetic binary operation (+, -, *, /)
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```block
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0+1;
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0-1;
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1*2;
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3/4;
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```
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### Absolute value
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```block
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Math.abs(-5);
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```
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### Minimum/maximum of two values
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```block
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Math.min(0, 1);
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```
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### Random value
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```block
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Math.random(5);
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```
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# Variables
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[Assign](/blocks/variables/assign) (set) a variable's value
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```blocks
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let x = 0;
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```
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Get a variable's value
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```blocks
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let x = 0;
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x;
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```
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[Change](/blocks/variables/change-var) a variable's value
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```blocks
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let x = 0;
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x+=1;
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```
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# Assignment Operator
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Use an equals sign to make a [variable](/blocks/variables/var) store the [number](/reference/types/number)
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or [string](/reference/types/string) you say.
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When you use the equals sign to store something in a variable, the equals sign is called
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an *assignment operator*, and what you store is called a *value*.
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### Storing numbers in variables
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This program makes the variable `item` equal `5` and then shows it on the [LED screen](/device/screen).
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````blocks
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let item = 5
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basic.showNumber(item)
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````
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### Storing strings in variables
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This program makes the variable `name` equal `Joe` and then shows it on the [LED screen](/device/screen).
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````blocks
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let name = "Joe"
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basic.showString(name);
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````
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### Notes
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You can use the assignment operator with variables of
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every [type](/reference/types). A *type* is which kind of thing
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a variable can store, like a number or string.
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### See also
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[variable](/blocks/variables/var), [types](/reference/types)
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# Change Value
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Set the value for local and global variables.
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### @parent blocks/change-value
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Change the value of a variable
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```blocks
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let x = 0
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x += 1
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```
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### Declare a variable
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Use the assignment operator to set the value of a [variable](/blocks/variables/var). Change the value of a variable from 0 to 1 using the change item block. Like this:
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```blocks
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let x = 0
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x += 1
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```
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### Example
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Use the assignment operator to set the value of a [variable](/blocks/variables/var). Change the value of a variable from 0 to 1 using the change item block. Then display the new value of the variable on the LED screen. Like this:
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```blocks
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let x = 0;
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x += 1;
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basic.showNumber(x);
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```
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### Notes
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* You can use the assignment operator with variables of each of the supported [types](/reference/types).
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### See also
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[variable](/blocks/variables/var), [types](/reference/types)
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@ -1,87 +0,0 @@
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# Local Variables
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How to define and use local variables.
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### @parent language
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A variable is a place where you can store and retrieve data. Variables have a name, a [type](/reference/types), and value:
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* *name* is how you'll refer to the variable
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* *type* refers to the kind of data a variable can store
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* *value* refers to what's stored in the variable
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### Var statement
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Use the Block Editor variable statement to create a variable
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and the [assignment operator](/blocks/variables/assign)
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to store something in the variable.
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For example, this code stores the number `2` in the `x` variable:
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```blocks
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let x = 2;
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```
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Here's how to define a variable in the Block Editor:
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1. Click `variables`.
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2. Change the default variable name if you like.
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3. Drag a block type on the right-side of the [assignment operator](/blocks/variables/assign) and click the down arrow to change the variable name.
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A variable is created for the number returned by the [brightness](/reference/led/brightness) function.
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```blocks
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let b = led.brightness();
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```
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### Using variables
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Once you've defined a variable, just use the variable's name whenever you need what's stored in the variable. For example, the following code shows the value stored in `counter` on the LED screen:
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```blocks
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let counter = 1;
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basic.showNumber(counter);
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```
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To change the contents of a variable use the assignment operator. The following code sets `counter` to 1 and then increments `counter` by 10:
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```blocks
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let counter = 1;
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counter = counter + 10;
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basic.showNumber(counter);
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```
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### Why use variables?
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If you want to remember and modify data, you'll need a variable.
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A counter is a great example:
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```blocks
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let counter = 0;
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input.onButtonPressed(Button.A, () => {
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counter = counter + 1;
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basic.showNumber(counter);
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});
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```
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### Local variables
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Local variables exist only within the function or block of code where they're defined. For example:
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```blocks
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// x does NOT exist here.
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if (led.brightness() > 128) {
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// x exists here
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let x = 0;
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}
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```
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#### Notes
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* You can use the default variable names if you'd like, however, it's best to use descriptive variable names. To change a variable name in the editor, select the down arrow next to the variable and then click "new variable".
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### See also
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[types](/reference/types), [assignment operator](/blocks/variables/assign)
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