Reading a button

/*

 Button with Internal Pullup

 Turns on and off a light emitting diode (LED) connected to digital pin 13,

 when pressing a pushbutton attached to pin 2.

 The circuit:

 - LED attached from pin 13 to ground through 220 ohm resistor

 - pushbutton attached to pin 2 from ground (no external resistors needed)

 - Note: on most Arduinos there is already an LED on the board attached to pin 13.

 https://docs.arduino.cc/built-in-examples/digital/Button/

*/

// constants won't change. They're used here to set pin numbers:

const int buttonPin = 2;  // the number of the pushbutton pin

const int ledPin = 13;    // the number of the LED pin

// variables will change:

int buttonState = 0;      // variable for reading the pushbutton status

void setup() {

 // initialize the LED pin as an output:

 pinMode(ledPin, OUTPUT);

 // initialize the pushbutton pin as an input with internal pullup:

 pinMode(buttonPin, INPUT_PULLUP); //creates an internal pullup resistor

}

void loop() {

 // read the state of the pushbutton value:

 buttonState = digitalRead(buttonPin);

 // check if the pushbutton is pressed.

 // With INPUT_PULLUP, a press pulls the pin to LOW:

 if (buttonState == LOW) {

   // turn LED on:

   digitalWrite(ledPin, HIGH);

 } else {

   // turn LED off:

   digitalWrite(ledPin, LOW);

 }

}