# Stopwatch

### @explicitHints true

## Introduction @unplugged

![A @boardname@ stopwatch toon image](/static/mb/projects/stopwatch.png)

This project turns the @boardname@ into a simple stopwatch. Pressing **A** starts the timer. Pressing **B** displays the elapsed seconds.

## {Step 1}

Add an event to run code when ``||input:button A is pressed||``.

```spy
input.onButtonPressed(Button.A, function () {
})
```

## {Step 2}

Add code inside the ``||input:button A is pressed||`` event to store the current
``||input:running time||`` in a variable ``||variables:start||``. This is the start time.

```spy
let start = 0
input.onButtonPressed(Button.A, function () {
    start = input.runningTime()
})
```

## {Step 3}

Add another event to run code when ``||input:button B is pressed||``.

```spy
input.onButtonPressed(Button.B, function () {
})
```

## {Step 4}

Add code in that event to compute the difference between the ``||input:running time||`` 
and ``||variables:value||`` time. This is the elapsed number of milliseconds since
pressing button A.

```spy
let start = 0
input.onButtonPressed(Button.B, function () {
    let elapsed = input.runningTime() - start
})
```

## {Step 5}

After setting the ``||variables:elapsed||`` time, add code to ``||basic:show||`` the
number of milliseconds ``||variables:elapsed||``. Use ``||Math:integer division||`` to
divide ``||variables:elapsed||`` by ``1000`` and get seconds.

```spy
let start = 0
input.onButtonPressed(Button.B, function () {
    let elapsed = input.runningTime() - start
    basic.showNumber(Math.idiv(elapsed, 1000))
})
```

## {Step 6}

Try your program in the simulator. Press **A** to start the stopwatch and press **B** to get the
current elapsed time. You can press **B** multiple times.

## {Step 7}

If you have a @boardname@ connected, click ``|Download|`` to transfer your code!