> 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/3.4-add-button-code.md).

# C-4 Add Button Code

Next, you'll add code in your Smart Light device app to control the LED using the push button.

The basic steps to use a push button in your app code are:

1. Declare a global variable to store the I/O pin number for the button.
2. Set the pin mode for the button pin in the `setup()` function.
3. Use a `digitalRead()` statement to check whether the button is currently pressed, and add code statements that should be performed if the button is pressed (or not pressed).

## Global Variable for Button Pin

Declare a global variable to store the I/O pin number for the button by adding this code statement **before** the `setup()` function:

```cpp
int button = D2;
```

If you connected your button to a different I/O pin other than `D2`, then modify this code statement to list the correct pin number for your button.

## Set Pin Mode for Button

Set the pin mode for your button pin by adding this code statement **within** the `setup()` function (between the curly braces):

```cpp
pinMode(button, INPUT_PULLUP);
```

## Turn On LED If Button Pressed

The `digitalRead()` method is used to check whether a button is currently pressed. 

The `digitalRead()` method will return a value of either `LOW` or `HIGH`:

* `LOW` indicates that the button is currently pressed.
* `HIGH` indicates that the button is **NOT** currently pressed.

A variable named `buttonState` will store the value returned by the `digitalRead()` method. 

An [if statement](http://www.wiring.org.co/reference/if_.html) will be used to **turn on** the LED if the button is being pressed (if `buttonState` has a value equivalent to `LOW`).

An [else statement](http://www.wiring.org.co/reference/else.html) will be included to **turn off** the LED if the button is **not** being pressed.

**Replace** all the existing code within the `loop()` function (everything **inside** its curly braces) with this code instead:

```cpp
    int buttonState = digitalRead(button);
    
    if(buttonState == LOW) {
        digitalWrite(LED, HIGH);
    }
    else {
        digitalWrite(LED, LOW);
    }
```

{% hint style="success" %}
**COPY CODE:**  Remember that you can copy a code block in this guidebook simply by clicking the **copy icon** in the upper right of the code block.
{% endhint %}

## 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:

* Confirm that the LED light that you connected to your Photon circuit board turns on when you press (and hold) the button – and turns off when the button is released.

Of course, nobody would want to continually press a button to keep a light turned on – however, this is a good way to verify that your button is connected correctly. In the next step, you'll modify the app code so the LED light toggles on or off with each button press.

## Troubleshooting Issues

If the LED does **not** turn on when the button is pressed, then there is a mistake in your app code – or a mistake in your wiring connection – or a mistake in both.

If the LED light is turned off and pressing the button has no effect, then verify that one of the button's legs is connected (via a jumper wire) to the same I/O pin number that is assigned to the `button` variable in your app code. If necessary, change either your wiring or your code, so the pin numbers match. If you revised your code, flash the updated app to your device.

If that still doesn't solve the issue, then double-check all your button wiring by referring back to the connection instructions.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.idew.org/code-internet-of-things/tutorials/create-smart-light/3.4-add-button-code.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.