root/pipe3.c

DEFINITIONS

1. main

#include<unistd.h>
#include<stdio.h>

int main() {

        int p,i;
        int fd1[2],fd2[2];
        char *messages[]={"3+4\n","5*6\n","10+100-(4*4)\n"};
        char result[100];

        pipe(fd1);
        pipe(fd2);
        if (p=fork()) {
                close(fd1[1]);
                close(fd2[0]);
                dup2(fd2[1],2);
                dup2(fd1[0],0);
                for (i=0;i<3;i++) {
                        fprintf(stderr,messages[i]);
                        fflush(stderr);
                        if (gets(result)) {
                                printf("%s\n",result);
                        }
                }

        } else {
                close(fd1[0]);
                close(fd2[1]);
                dup2(fd1[1],1);
                dup2(fd2[0],0);
                execl("/usr/bin/bc","bc","-q",(char *)0);
        }

        return 0;
}