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Local Variables

How to define and use local variables.

@parent language

A variable is a place where you can store and retrieve data. Variables have a name, a type, and value:

name is how you'll refer to the variable
type refers to the kind of data a variable can store
value refers to what's stored in the variable

`var` and `let` statement

The var keyword declares a global variables that is defined within the entire scope of the function. The let keyword defined a block-scoped variable, similarly to other languages like Java, C# or C.

For example, this code stores the number 2 in the num1 variable:

number variable

let num1 = 2

string variable

let name = "Mike"

boolean variable

let bool = true

image variable

let img = images.createImage(`
. . # . .
. # # # .
# # # # #
. # # # .
. . # . .
`)

See Image for info on creating and using image variables.

Using variables

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:

let counter = 5;
basic.showNumber(counter, 100)

To change the contents of a variable use the assignment operator :=. The following code sets counter to 1 and then increments counter by 10:

let counter = 0;
counter = 1
counter = counter + 10

Why use variables?

Variables help simplify your code. For example, instead of turning on LEDs one by one like this:

led.plot(0, 0)
led.plot(1, 1)
led.plot(2, 2)
led.plot(3, 3)
led.plot(4, 4)

You can use a variable (i) and a for loop to plot the same series of points (i is incremented by 1, each time the loop repeats):

for (let i = 0; i < 5; i++) {
    led.plot(i, i)
}

Local vs global variables

Local variables exist only within the function or block of code where they're defined. Local variables don't exist outside of where they're defined. For example:

if (led.brightness() > 127) {
    let y = 1
    // `y` variable exists here
} else {
    // `y` variable does not exist here
}

Use global variables when you need to access a variable in nested code blocks or across multiple functions.

Lessons

guess the number, digi yoyo, rock paper scissors, love meter

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