// Der Vater erzeugt 3 Kindprozesse (der erste addiert, der zweite multipliziert, der dritte
// dividiert), und Rechnet den Ausdruck (1+2)*3/4 aus.

 #include <sys/types.h>
 #include <unistd.h>
 #include <stdio.h>       
int main(){
int x,i,a=1,b=2,c=3,d=4;

int pfd[2],pfd1[2],pfd2[2],pfd3[2];


pipe(pfd);
pipe(pfd1);
//pfd[0];
//pfd[1];
//if (fork()==0){}
  switch(fork()){ 
   case 0:{//Kind1 (+)
      close(pfd1[1]);close(pfd[0]);
      read(pfd1[0],&a,sizeof(int));
      read(pfd1[0],&b,sizeof(int));
      a+=b;
      write(pfd[1],&a,sizeof(int));
      
       
      exit(0);}
   default://Vater
     {close(pfd1[0]);
      pipe(pfd2);
      switch(fork()){
      case 0://Kind2 (*)
       read(pfd2[0],&a,sizeof(int));
       read(pfd2[0],&b,sizeof(int));
       a*=b;
       write(pfd[1],&a,sizeof(int));
      
      exit(0);
      default:{//Vater
      pipe(pfd3);
      close(pfd2[0]);
      switch(fork())
      {
       case 0://Kind3 (/)
       {
        close(pfd3[1]);
        close(pfd1[1]);//...
        read(pfd3[0],&a,sizeof(int));
        read(pfd3[0],&b,sizeof(int));
        a/=b;
        write(pfd[1],&a,sizeof(int));
        exit(0);
       }
       default:{//Vater
       write(pfd1[1],&a,sizeof(int));
       write(pfd1[1],&b,sizeof(int));
       read(pfd[0],&x,sizeof(int));
       
       write(pfd2[1],&x,sizeof(int));
       write(pfd2[1],&c,sizeof(int));
       read(pfd[0],&x,sizeof(int));
                     
       write(pfd3[1],&x,sizeof(int));
       write(pfd3[1],&d,sizeof(int));
       read(pfd[0],&x,sizeof(int));
       
       printf("Ergebnis:%d\n",x);              
      } 
      } 
       }
      }
  }
}

}