const int buttonPin = 2;
const int ledPin = 13;
int ledState = HIGH;         
int buttonState;             
int lastButtonState = LOW;   
unsigned long lastDebounceTime = 0;
unsigned long debounceDelay = 50;    //debounce time; 

void setup() 
{
  pinMode(buttonPin, INPUT);
  pinMode(ledPin, OUTPUT);
  digitalWrite(ledPin, ledState); // initial LED state
}

void loop() 
{
  int reading = digitalRead(buttonPin);
  if (reading != lastButtonState) {
    lastDebounceTime = millis();
  }
  if ((millis() - lastDebounceTime) > debounceDelay) {
    if (reading != buttonState) {
      buttonState = reading;
      if (buttonState == HIGH) {
        ledState = !ledState;
      }
    }
  }
  digitalWrite(ledPin, ledState);
  lastButtonState = reading;
}