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

int main(void)
{
    int pid,
        c_fd[2],
        p_fd[2];

    char *str;

    if (pipe(c_fd) == -1 || pipe(p_fd) == -1)
    {
        fprintf(stderr, "Pipe failed.\n");
        exit(1);
    }

    pid = fork();
    if (pid == -1)
    {
        fprintf(stderr, "Fork failed.\n");
        exit(1);
    }
    // child process
    else if (pid == 0)
    {
        // redirect stdin to c_fd output and close c_fd input
        dup2(0, c_fd[0]);
        close(c_fd[1]);

        // redirect stdout to p_fd input and close p_fd output
        dup2(1, p_fd[1]);
        close(p_fd[0]);

        while (read(c_fd[0], &str, 11) != 0)
            if (strcmp(str, "Guten Tag!\n") == 0)
                printf("Oh, hallo!\n");

        exit(0);
    }
    // parent process
    else
    {
        // redirect stdout to c_fd input and close c_fd output
        dup2(1, c_fd[1]);
        close(c_fd[0]);

        // redirect stdin to p_fd output and close p_fd input
        dup2(0, p_fd[0]);
        close(p_fd[1]);

        printf("Guten Tag!\n");

        wait(&pid);

        printf("Kindprozess hat erfolgreich geantwortet!\n");
    }

    return 0;
}