(a)
  #include "avr/io.h"
  int main ( )
  {
    ddrb &= ~(1<<0);    
    ddrb = ddrb|(1<<3);  
    ocr0 = 3;      
    tcnt0 = 0;      
    tccr0 = 0x36;    
    while (1);
    return 0;
  }
  
  (b)
  #include "avr/io.h"
  int main ( )
  {
    ddrb &= ~(1<<0);    
    ddrb = ddrb|(1<<3);  
    ocr0 = 3;      
    tcnt0 = 0;    
    tccr0 = 0x1e;    
    while (1);
    return 0;
  }