//For a given N value (5<N<=15) create N processes.
//The main process creates a new subprocess. This subprocess will create another subprocess,
//and so on until N processes are created.
//Each process will discuss with his child using a pipe channel.
//The main process (the initial one) will generate a random number between 1000 and 10000 and will start the game.
//The game will start after all the processes are created.
//Each process will subtract a random value (between 10 and 20) and sends the new number to his child.
//The child will perform the same operation and send the number further.
//The game ends when the number reaches the last child. This process will only print the received number.

#include<unistd.h>
#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#include<errno.h>
#include<sys/types.h>
#include<sys/wait.h>

int main(){

        int pp[15][2], N, rNumber, a, f, k, j;
		k = 0;

        printf("n=");
        srand(time(0)); //random generator
        scanf("%d", &N);

        pipe(pp[k]);  //

        rNumber = rand() % 9000 + 1000;
        write(pp[k][1], &rNumber, sizeof(int));
        printf("The generated number is: %d\n", rNumber);
		f = fork();
        int i;
        for (i=0; i<N; i++){
				if( f < 0 ) {
					perror("fork error");
					exit(1);
				}
                if( f == 0 ) { //we are in the "child" process
                        if( i != N-1 ){ //I checked if I didn't reach the last process
                                read(pp[k][0], &rNumber, sizeof(int));
								k++;
								pipe(pp[k]);
                                srand(time(0));
                                a = rand() % 10 + 10;
                                printf("I'm an intermediate process and I decrease with the value: %d\n", a);
                                rNumber = rNumber - a;
                                write(pp[k][1], &rNumber, sizeof(int));
								sleep(1);
                                f = fork();
								if (f != 0){
									wait(0);
									exit(0);
								}
                        }
                        else{ //last process
								read(pp[k][0], &rNumber, sizeof(int));
                                printf("I'm the last process and the final result is: %d\n", rNumber);
								for (j=0; j<k; j++){
									close(pp[k][0]);
									close(pp[k][1]);
									wait(0);
									exit(0);
								}
                        }
                }

        }
		wait(0);
		exit(0);
        return 0;
}