Code:
DDRB |= (1<<PB4) //output LED
PORTB &= ~(1<<PB4) //set PB4 low, LED off

DDRB &= (1<<PB1) //input switch
PORTB != (1<<PB1) //pullup for switch

while(1)
{
   if (bit_is_clear(PINB, PB1)
      PORTB |= (1<<PB4); //turn LED on
   else
      PORTB &= ~(1<<PB4); //turn LED off
}