const int buttonPin = 4; 
const int ledPin = 12; 
int buttonState; 
void setup() 
{ 
pinMode(ledPin, OUTPUT);  
pinMode(buttonPin, INPUT); 
} 
void loop() { buttonState = digitalRead(buttonPin); 
if(buttonState == LOW) { 
digitalWrite(ledPin, HIGH); 
delay(500);
digitalWrite(ledPin, LOW);
delay(500);
} 
else 
{ 
digitalWrite(ledPin, LOW); 
} 
}