using namespace std;
#include <iostream>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>

void mult(int x, int y, int id);

void sub(int x, int y, int id);

void add(int x, int y, int id);

int main(int argc, char * argv[])
{
    int pid;
    cout << "Parent's PID: " << getpid() << endl;
    pid = fork();
    if (pid == 0 ) // child1
	{
        int pidChild2;
		sub(4, 5, getpid());

        // child1 subtracts numbers
        pidChild2 = fork(); // child2
        if (pidChild2 == 0)
        {
            add(4, 5, getpid()); 
            exit(0);
        }
        else // child1
        {
            wait(0);
            mult(4, 5, getpid());
            exit(0);
        }
	}
    else // parent of both
    {
        wait(0);
    }
}

void mult(int x, int y, int id)
{
    cout << "4*5 = " << x*y << endl;
    cout << "Child1's ID: " << id << endl;
}

void sub(int x, int y, int id)
{
    cout << "4-5 = " << x-y << endl;
    cout << "Child1's ID: " << id << endl;
}


void add(int x, int y, int id)
{
    cout << "4+5 = " << x+y << endl;
    cout << "Child2's ID: " << id << endl;
}