const int LED_PIN=13;
const int BUTTON_PIN=7;

int ledState=LOW;
int lastButtonState;
int buttonState;

unsigned long lastDebounceTime=0;
unsigned long debounceDelay=50;

void setup() {
  pinMode(LED_PIN,OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  digitalWrite(LED_PIN,OUTPUT);
  lastButtonState=digitalRead(BUTTON_PIN);
}

void loop() {
  int reading=digitalRead(BUTTON_PIN);
  if(reading!=lastButtonState){
    lastDebounceTime=millis();
  }
  if((millis()-lastDebounceTime)>debounceDelay){
    if(reading!=buttonState){
      buttonState=reading;
      if(buttonState==LOW){
        ledState=!ledState;
        digitalWrite(LED_PIN,ledState);
      }
    }
  }
  lastButtonState=reading;
}