pxt-calliope/docs/lessons/counter.md

# Counter lesson

Learn how to create a counter with with **on button** pressed.

## Topic

Variables

## Quick Links

* [activity](/lessons/counter/activity)
* [challenges](/lessons/counter/challenges)
* [quiz](/lessons/counter/quiz)
* [quiz answers](/lessons/counter/quiz-answers)

## Prior learning and lesson level

Learn how to create a **variable** to keep track of the current count. We will be learning how to create a counter app using a variable and simple commands, such as on button pressed, and show number.

## Documentation

```cards
input.compassHeading()
basic.forever(() => {})
let x = 0
if (true) {}
basic.showString("Hello!")
basic.showLeds(`
    . . . . .
    . . . . .
    . . # . .
    . . . . .
    . . . . .
    `)
```

* **[variable](/blocks/variables)**:
* **[arithmetic operators](/types/number)**
* **[on button pressed](/reference/input/on-button-pressed)**
* **[show number](/reference/basic/show-number)**

## Objectives

* learn how to create a variable as a place where you can store data so that you can use it later in your code, accessible across all functions, and in nested code blocks
* learn how arithmetic operators operate on numbers and return a number
* learn how to run code when an input button is pressed
* learn how to show a number on the LED screen, one digit at a time (scrolling from left to right)