Output of Forking in C - operating-system

Question

Given PID = 4224
Why am I getting output of the following snippet of code as :
x = 10922 y = 0
I am process: 10923
x = 0 y = 2
I am process: 10922
x = 0 y = 2
I am process: 10922
x = 0 y = 0
I am process: 10924
For this code :
#include <iostream>
#include <stdio.h>
#include <unistd.h>
int main() {
int x = 1, y = 2;
int pid;
x=fork();
if(x==0){
printf("x = %d y = %d\n", x, y);
pid = getpid();
printf("I am process: %d\n", pid);
}
y = fork();
if(y==0){
printf("x = %d y = %d\n", x, y);
pid = getpid();
printf("I am process: %d\n", pid);
}
return 0;
}

Answer 1

Lets start with this, the output of your program:
x = 0 y = 2
I am process: 330161
x = 330161 y = 0
I am process: 330162
x = 0 y = 0
I am process: 330163
Notice that the order is a bit different from yours. That is because which process runs first is environment dependent. So, lets fix your program up a bit to be more lucid:
#include <stdio.h>
#include <unistd.h>
int main() {
int x = 1, y = 2;
int pid;
x=fork();
if(x==0){
pid = getpid();
printf("1:x = %d y = %d I am process %d\n", x, y, pid);
}
fflush(NULL);
y = fork();
if(y==0){
pid = getpid();
printf("2:x = %d y = %d I am process %d\n", x, y, pid);
}
return 0;
}
By placing the printfs together with a single newline, we can rest assured that each statement belongs to one process, they are not interleaved.
By adding an indicator at the beginning of the line 1:, 2: we know which printf() they came from. The fflush() prevents the child process from inheriting any partially buffered writes from stdio -- not a problem if you are on a terminal, but if you redirect to a file you might find duplicated lines. So the output on my system looks like:
1:x = 0 y = 2 I am process 330214
2:x = 330214 y = 0 I am process 330215
2:x = 0 y = 0 I am process 330216
From that, the first child process of the main one is 330214. The second is 330215; and the grand-child (child of child) is 330216.
I hope that gives you enough to work out your answers.
Don't be afraid to play with these example programs. It is a good way to learn about the workings of your system.