#include <avr/io.h>

typedef struct
{
  unsigned int bit0:1;
  unsigned int bit1:1;
  unsigned int bit2:1;
  unsigned int bit3:1;
  unsigned int bit4:1;
  unsigned int bit5:1;
  unsigned int bit6:1;
  unsigned int bit7:1;
} _io_reg;

#define REGISTER_BIT(rg,bt) ((volatile _io_reg*)&rg)->bit##bt


#define BUTTON_PIN  REGISTER_BIT(PINB,3)
#define LED_PORT    REGISTER_BIT(PORTB,4)

#define BUTTON_DIR  REGISTER_BIT(DDRB,3)
#define LED_DIR     REGISTER_BIT(DDRB,4)
 
main() {
  uint8_t is_button = BUTTON_PIN;
 
  LED_DIR = 1;
  BUTTON_DIR = 0;

  while (1) {
    LED_PORT = BUTTON_PIN;
  }
}