#include <stdio.h>
#include <unistd.h>
#include <sys/wait.h>

int cnt;

int query(int a)
{
    cnt++;
    return a;
}

int main()
{
    int fd[2];
    pipe(fd); //init pipe
    int pid=fork(); //create a copy of our process
    if (pid) //parent process
    {
        close(fd[1]); //close write descriptor

        int result;
        if (pid!=-1)
        {
            waitpid(pid,0,0); //wait for child to finish

            read(fd[0], &result, sizeof(result)); //read result
        }
        else
        {
            fprintf(stderr,"forking failed..\n");
            return 1;
        }
        printf("parent used %d calls\n",cnt);
        printf("result = %d\n",result);
    }
    else //child process
    {
        close(fd[0]); //close read descriptor

        //compute result with a suboptimal amount of calls
        int result=0;
        for (int i=0; i<10; i++)
            result+=query(i);

        printf("child used %d calls\n",cnt);

        write(fd[1], &result, sizeof(result)); //send result
    }
    return 0;
}