55 lines
2.0 KiB
Markdown
55 lines
2.0 KiB
Markdown
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# Stop watch
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This project turns the @boardname@ into a simple stop-watch. You can use it the [Watch project]
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if you've build it already. Pressing **A** will start the timer
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and pressing **A** again will display the resulting time. Let's get started.
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## Program state
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The stop watch has two states: it is either stopped or measuring time.
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Let's create a new variable ``start_time`` to track the state:
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* if ``start_time`` is equal to ``0``, the watch is stopped.
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* if ``start_time`` is **not** equal to ``0``, the watch is running and the value of ``start_time`` is
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the time it started.
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## Pseudo code
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The rough outline of the code is as follows: when a user presses **A**, we start by determining in which
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state we are. If the watch is stopped (``start time`` is 0), we start the counter and store the current time. If the watch is running (``start time`` is not 0), we compute the duration and reset ``start time`` to 0.
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The ``||input:runningTime||`` block returns the number of **milli**-seconds elapsed since the @boardname@ was turned on. To compute the duration in seconds, we use the following formula:
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duration in seconds = (current time - start time) / 1000.0
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In pseudo code, this could look like this:
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```
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on button pressed
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if start time is 0
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store current time into start time
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else
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show duration
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reset start time
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```
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If you translate the pseudo-code line by line into blocks, it might end up like this.
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```blocks
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let start_time = 0
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input.onButtonPressed(Button.A, function () {
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// is the watch running?
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if (start_time == 0) {
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// store current time
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start_time = input.runningTime()
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basic.showIcon(IconNames.Butterfly)
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} else {
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// compute duration and display it
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basic.showNumber(Math.idiv(input.runningTime() - start_time, 1000))
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// reset watch state
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start_time = 0
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}
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})
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start_time = 0
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```
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