#define BUTTON_PIN 21 // GPIO21 pin connected to button
#define ledpin 2
// Variables will change:
int lastState = HIGH; // the previous state from the input pin
int currentState;     // the current reading from the input pin

void setup() {
  Serial.begin(9600);
  // initialize the pushbutton pin as an pull-up input
  pinMode(BUTTON_PIN, INPUT_PULLUP);
   pinMode(ledpin,OUTPUT);
}

void loop() {
  // read the state of the switch/button:
  currentState = digitalRead(BUTTON_PIN);

 if (lastState == HIGH && currentState == LOW){
    Serial.println("The button is pressed");
    digitalWrite(ledpin, HIGH);
 }
  else if (lastState == LOW && currentState == HIGH){
    Serial.println("The button is released");
    digitalWrite(ledpin,LOW);
  }

  // save the last state
  lastState = currentState;
}