Declaring variables

How to declare and use variables.

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

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

The variable (var) statement

A variable is created using a variable statement. The variable will “declare” itself in this statement. In MakeCode JavaScript a variable is declared along with its first assignment:

let x = 2

With Python a variable is declared when it’s first used. In this case the variable statement is just the assignment of the variable:

x = 2

If a variable is declared in blocks you will see the ||variables:set|| block with the first use of the variable. This code stores the number 2 in the x variable:

let x = 2

The new variable is created inside the ||variables:Variables|| category of the Toolbox.

Creating a variable from the Toolbox

In the ||variables:Variables|| category of the Toolbox you can create new variable:

Create a new variable

Here’s how to create a variable using the Toolbox:

Click ||variables:Variables|| in the Toolbox.
Click on Make a Variable….
Choose a name for your variable, type it in, and click Ok.
Drag the new variable, ||variables:set|| or ||variables:change|| block into your code.

Quick example

A variable is created for the number returned by the brightness function.

let b = led.brightness()

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 = 1
basic.showNumber(counter)

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 = 1
counter = counter + 10
basic.showNumber(counter)

Why use variables?

If you want to remember and modify data, you’ll need a variable. A counter is a great example:

let counter = 0
input.onButtonPressed(Button.A, function () { 
    counter = counter + 1
    basic.showNumber(counter)
})

Local variables

Local variables exist only within the function or block of code where they’re defined. For example:

// x does NOT exist here.
if (led.brightness() > 128) {
    // x exists here
    let x = 0
}

Notes about variables

Variable names

Some blocks come from the Toolbox with default variable names, such as list from ||arrays:Arrays||. You can use the default variable names if you 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 “Rename variable…” to change it.

Hidden declaration block

If a variable is used more than once, and its declaration block sets the variable to 0, that first declaration block is hidden. For example:

let x = 0
if (x == 0) {
    x = 9
}

You don’t see any first block setting the variable x to 0 but that happens in its hidden declaration statement. You’ll see the declaration statement, let x = 0, if you switch from Blocks to JavaScript in the Editor:

let x = 0
if (x == 0) {
    x = 9
}