#include <avr/io.h> // header file file for input output pins
#include <util/delay.h> // header file for delay.


int main (void)
{
 /* set pin 4 of PORTB for output*/
 DDRB |= _BV(DDB4);




 while(1) {

  /* set pin 4 high to turn led on */
  PORTB |= _BV(PORTB4);
  _delay_ms(1000); //delay 1 second

  /* set pin 4 low to turn led off */
  PORTB &= ~_BV(PORTB4);
  _delay_ms(1000); //delay 1 second.
 }
 }