#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main(void) {
  pid_t pid;
  int pfdw[2];
  int pfdr[2];
  int nc, status;
  char expresion[100];
  char respuesta[100];
  
  if (pipe(pfdw) < 0) {
    perror("pipe");
    exit(1);
  }
  if (pipe(pfdr) < 0) {
    perror("pipe");
    exit(1);
  }

  if ((pid = fork()) < 0) {
    perror("fork");
    exit(1);
  }

  if (pid == 0) {
      /* Attach standard input to the end of the pipe where parent write. */
    dup2(pfdw[0], 0);
    close(pfdw[1]);
      /* Attach standard output to the end of the pipe where parent read. */
    dup2(pfdr[1],1);
    close(pfdr[0]);
    execlp("bc", "bc", 0);
    perror("exec");
    _exit(127);
  }

  close(pfdw[0]);
  close(pfdr[1]);

  do
  {
    nc=read(STDIN_FILENO, expresion, sizeof(expresion));
    expresion[nc]='\n';
    write(pfdw[1], expresion, nc+1);
    nc=read(pfdr[0], respuesta, sizeof(respuesta));
    write(STDOUT_FILENO, respuesta, nc);
  } while (strncmp(expresion, "quit", 4)!=0);
  close(pfdw[1]);
  close(pfdr[0]);
  waitpid(pid, &status, 0);
  exit(0);
}