const int buttonPinA = 2;
const int ledPinA = 3;

int ledStateA = HIGH; //the current state of the output pin
int buttonStateA; //the current reading from the input pin
int lastButtonStateA = LOW; //the previous reading from the input pin

unsigned long lastDebounceTimeA = 0;

// one constant for all buttins is probably OK
// this absurdly large "debounce" constant dose not impact repsonse time!
// use 50 in real deployment, here just for illustrative purposes I use 500

const unsigned long theDebounceDelay = 500;

void setup() {
pinMode (buttonPinA, INPUT_PULLUP);
pinMode (ledPinA, OUTPUT);

digitalWrite(ledPinA, ledStateA);
}

void loop() {
  int reading = digitalRead(buttonPinA);

  if ((millis() - lastDebounceTimeA) > theDebounceDelay) {

    if (reading != buttonStateA) {
      buttonStateA = reading;

      if (buttonStateA == LOW) {      // I like the press, not the release to take action
        ledStateA = !ledStateA;
      }

      lastDebounceTimeA = millis();   // don't act on the switch again until the debounce period has passed
    }
  }
  digitalWrite(ledPinA, ledStateA);
  lastButtonStateA = reading;
}