const int buttonPin = 2;
const int ledPin =  8;

volatile int buttonState = LOW;

void setup()
{
  Serial.begin(9600);
  pinMode(ledPin, OUTPUT);
  pinMode(buttonPin, INPUT);
  attachInterrupt(0, pin_ISR, CHANGE);
}

void loop()
{
  Serial.print(buttonState);
}

void pin_ISR()
{
  if (buttonState == LOW)
  {
    buttonState = HIGH;
    digitalWrite(ledPin, HIGH);
  }
  else
  {
    buttonState = LOW;
    digitalWrite(ledPin, LOW);
  }
}