#include <stdio.h>   /* Standard input/output definitions */
#include <string.h>  /* String function definitions */
#include <unistd.h>  /* UNIX standard function definitions */
#include <fcntl.h>   /* File control definitions */
#include <errno.h>   /* Error number definitions */
#include <termios.h> /* POSIX terminal control definitions */
int main(void)
{
      FILE *input;
      FILE *output;
      input = fopen("/dev/tty", "r");      //open the terminal keyboard
      output = fopen("/dev/tty", "w");
      int fd; /* File descriptor for the port */
      fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);
      if (fd == -1)
      {
       /*
    * Could not open the port.
    */
    perror("open_port: Unable to open /dev/ttyS0 - ");
      }
      else
    {
        int c=fgetc(input);
        while(c!=0)
        {
            fputc(c,output);//output to screen
            write(fd, c, 1);//write to port
            c=fgetc(input);//get char from keyboard
            fcntl(fd, F_SETFL, 0);//read from port

        }
      printf("%d",fd);
    return (fd);
   }