Pure C Language In Arduino Uno (Sample Code 3) [Digital Read]

test.c

/*
    Compiling and uploading to Arduino Uno (Sample Code 3) [Digital Read]
    =====================================================================

    avr-gcc -Os -mmcu=atmega328p -c test.c
    avr-gcc -mmcu=atmega328p -o test.elf test.o
    avr-objcopy -O ihex -R .eeprom test.elf test.hex
    avrdude -F -V -c arduino -p ATMEGA328P -P /dev/cu.usbmodem1421 -b 115200 -U flash:w:test.hex

*/
#ifndef F_CPU
#define F_CPU 16000000UL //set frequency
#endif

#include <avr/io.h>
#include <util/delay.h>

#define MS_DELAY 500 //500 milliseconds

int main() {
  DDRB |= _BV(DDB0); //set pin 8 to output
  DDRB &= ~_BV(DDB1); //set pin 9 to input
  
  for(;;) {

    int val = PINB & _BV(PB1);

    if(val == 0) {
      PORTB |= _BV(PORTB0); //set pin 8 to high  
    } else {
      PORTB &= ~_BV(PORTB0); //set pin 8 to low
    }

    _delay_ms(MS_DELAY); //delay

  }
  
  return 0;
}