Visually what happens to fork() in a For Loop

I have been trying to understand fork() behavior. This time in a for-loop. Observe the following code:

#include <stdio.h>

void main()
{
   int i;

   for (i=0;i<3;i++)
   {
      fork();

      // This printf statement is for debugging purposes
      // getppid(): gets the parent process-id
      // getpid(): get child process-id

      printf("[%d] [%d] i=%dn", getppid(), getpid(), i);
   }

   printf("[%d] [%d] hin", getppid(), getpid());
}

Here is the output:

[6909][6936] i=0
[6909][6936] i=1
[6936][6938] i=1
[6909][6936] i=2
[6909][6936] hi
[6936][6938] i=2
[6936][6938] hi
[6938][6940] i=2
[6938][6940] hi
[1][6937] i=0
[1][6939] i=2
[1][6939] hi
[1][6937] i=1
[6937][6941] i=1
[1][6937] i=2
[1][6937] hi
[6937][6941] i=2
[6937][6941] hi
[6937][6942] i=2
[6937][6942] hi
[1][6943] i=2
[1][6943] hi

I am a very visual person, and so the only way for me to truly understand things is by diagramming. My instructor said there would be 8 hi statements. I wrote and ran the code, and indeed there were 8 hi statements. But I really didn’t understand it. So I drew the following diagram:

Diagram updated to reflect comments :)

Observations:

1. Parent process (main) must iterate the loop 3 times. Then printf is called
2. On each iteration of parent for-loop a fork() is called
3. After each fork() call, i is incremented, and so every child starts a for-loop from i before it is incremented
4. At the end of each for-loop, "hi" is printed

Here are my questions:

• Is my diagram correct?
• Why are there two instances of i=0 in the output?
• What value of i is carried over to each child after the fork()? If the same value of i is carried over, then when does the "forking" stop?
• Is it always the case that 2^n - 1 would be a way to count the number of children that are forked? So, here n=3, which means 2^3 - 1 = 8 - 1 = 7 children, which is correct?