> For the complete documentation index, see [llms.txt](https://docs.idew.org/code-internet-of-things/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.idew.org/code-internet-of-things/tutorials/create-smart-light/3.6-particle-cloud-code.md).

# C-6 Particle Cloud Code

Next, you'll modify your Smart Light device app to allow a web app to interact with your Photon through the internet.

## Particle Cloud

All of your Photon's internet communications are routed through the Particle Cloud service, which offers these ways that a web app can interact with a Photon device through Particle Cloud:

1. A web app can **get the value of a Photon device variable**
2. A web app can **call a custom function on a Photon device**
3. A web app can **get event notifications from a Photon device**

![](/files/-LIRThHnT2hl6kqfW1FZ)

The web app that you'll be creating for your Smart Light device will perform these two tasks:

1. The web app will display whether the LED light is currently turned on or off. The web app will do this by getting the current value of the `lightStatus` variable in your Photon device app.
2. The web app will display a button that can be clicked to remotely turn the LED light on or off. The web app will do this by calling the `toggleLight()` function in your Photon device app.

You'll need to add some code to your Photon device app that will allow your web app to get the value of the `lightStatus` variable and to call the `toggleLight()` function.

## Share Device Variable

In order for a web app to get the value of Photon device variable, your Photon device app must share the variable through Particle Cloud using the `Particle.variable()` method.

Share the `lightStatus` variable through Particle Cloud by adding this code statement **within** the `setup()` function of your Photon app:

```cpp
Particle.variable("lightStatus", lightStatus);
```

This `Particle.variable()` code statement creates a "cloud variable" that stores the value of your Photon device variable. Whenever the value of the device variable changes in your Photon app, the value stored in the cloud variable will be automatically synced to match.

The `Particle.variable()` method requires two parameters inside its parentheses (in this order):

1. **The cloud variable name**, which can be up to 12 characters in length. If possible (for simplicity), make your cloud variable name match your device variable name. However, the cloud variable is allowed to have a different name. The cloud variable name must be listed within double quotation marks. In this case, `"lightStatus"` will be the name of the cloud variable (which matches the device variable name).
2. **The Photon device variable name**, which is the variable in your Photon app whose value will be shared in Particle Cloud. In this case, you're sharing the value of the `lightStatus` variable.

## Share Device Function

In order for a web app to call a function that runs on your Photon device, your Photon device app must share the function through Particle Cloud using the `Particle.function()` method.

Share the `toggleLight()` function through Particle Cloud by adding this code statement **within** the `setup()` function of your Photon app:

```cpp
Particle.function("toggleLight", toggleLight);
```

This `Particle.function()` code statement creates a "cloud function" that is a reference to the custom function in your Photon device app. Whenever your web app calls the cloud function, the corresponding device function in your Photon app will automatically be called.

The `Particle.function()` method requires two parameters inside its parentheses (in this order):

1. **The cloud function name**, which can be up to 12 characters in length. If possible (for simplicity), make your cloud function name match your device function name. However, the cloud function is allowed to have a different name. The cloud function name must be listed within double quotation marks **without** parentheses after its name. In this case, `"toggleLight"` will be the name of the cloud function (which matches the device function name).
2. **The Photon device function name**, which is the custom function in your Photon device app that will be shared through Particle Cloud. List the function name **without** parentheses after its name. In this case, you're sharing the `toggleLight` function in your Photon app.

## Modify Device Function

A Photon device function that is shared through Particle Cloud **must** do the following:

* The Photon function must **accept a String parameter** when the function is called.
* The Photon function must **return an integer value** when the function is performed.

Currently, the `toggleLight()` function does **not** do these things – but you can easily modify the function to work with Particle Cloud with these minor changes:

1. Change `toggleLight()` to `toggleLight(String data)`. This adds a parameter inside the parentheses that will be accepted when the function is called: `String` is the data type for the parameter (a text string), and `data` is the name of a local variable that will store the parameter value (the text string). If desired, you could use a different name other than `data`.
2. In front of the function name, change `void` to `int`. This indicates that the function will return an integer value (whole number), instead of no value (which is what `void` represents).
3. Add the code statement `return 1;` inside the function at the end before the closing curly brace. This code statement will return an integer value of 1 whenever the function is performed. This is the simplest way to ensure the function returns an integer value.

Your custom function should look like this now:

```cpp
int toggleLight(String data){
    if (lightStatus == "off") {
        digitalWrite(LED, HIGH);
        lightStatus = "on";
    }
    else {
        digitalWrite(LED, LOW);
        lightStatus = "off";
    }
    return 1;
}
```

You might notice that there aren't any code statements within the curly braces of the `toggleLight()` function that actually use the `data` parameter variable. That's actually okay – the function does have to accept a String parameter, but it **doesn't** have to use the parameter inside in the function.

However, depending on what a custom function is supposed to do, the text string passed into the `data` parameter could be used to decide what action(s) are performed within the custom function. In this case, you won't do that, but it is an option that's available.

## Modify Call to Function

Once a custom function in your Photon device app has been modified to be shared through Particle Cloud, your Photon app (and your web app) **must** include a text string when calling the function.

In your Photon app, there's just one code statement that calls the `toggleLight()` function. Inside the `loop()` function, there is an `if` statement that calls the `toggleLight()` function when the button is pushed (`buttonState == LOW`):

* Inside this `if` statement, change `toggleLight();` to `toggleLight("data");`

In this case, `"data"` will be the text string passed into the parameter when this function is called. However, since this function **doesn't** actually do anything with the parameter value, this text string could be **any text** listed within double quotation marks – even an **empty** text string of `""` would work.

## Flash App to Device

Flash your app code to your Photon device by clicking the **Flash** icon in the left navigation bar. 

Once your Photon has downloaded the app and restarted, the updated app will start running. You shouldn't notice any visible changes in the device's behavior, but your Photon app will now be sharing the `lightStatus` variable and `toggleLight()` function with Particle Cloud.

* Confirm that the LED light **still** toggles between "on" and "off" each time the button is pressed.


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