#include <errno.h>  //perror()
#include <stdio.h>  //perror()
#include <stdlib.h> //exit(), atoi()
#include <unistd.h> //read(), write()
#define BUFF_SIZE 4096

int main(int argc, char const *argv[]) {
  int first = 0;
  int second = 0;
  int sum = 0;
  int n = 0;
  char buffer[BUFF_SIZE];

  printf("Inserisci il primo addendo (-1 per uscire):\n");
  while (((n = read(STDIN_FILENO, buffer, BUFF_SIZE)) > 0) &&
         ((first = atoi(buffer)) != -1)) {
    printf("Inserisci il secondo addendo:\n");
    if (read(STDIN_FILENO, buffer, BUFF_SIZE) == -1) {
      perror(argv[0]);
      exit(EXIT_FAILURE);
    }

    second = atoi(buffer);
    sum = first + second;

    printf("La somma e:\n");

    int size_byte = sprintf(buffer, "%d", sum);
    if (write(STDOUT_FILENO, buffer, size_byte) == -1) {
      perror(argv[0]);
      exit(EXIT_FAILURE);
    }

    printf("\n\nInserisci il primo addendo (diverso da -1):\n");
  }

  if (n == -1) {
    perror(argv[0]);
    exit(EXIT_FAILURE);
  }
  exit(EXIT_SUCCESS);
}