How many processes are created in this c programme?

Question

This is the example I was given and I was asked how many processes are created.

c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(void){
    int pid = (int)fork();
    pid = fork();
    pid = fork();
    printf("%d\n", pid);
    if (pid == 0){
        fork();
    }
    fork();

    return 0
}

Initially I see 5 forks so 2^5 - 1 = 31 processes. However it quickly became apparent that was not the case as the if (pid == 0){ fork(); } throws me off.

I modified the code to get some sort of count:

c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int count = 1;

int main(void){
    int pid = (int)fork(); 
    pid = fork(); 
    pid = fork(); 
    if (pid == 0){ 
       printf("2 ");
       fork(); 
    }
    fork(); 
    printf("1 ");
    return 0;
}

Result:
1 1 1 1 2 1 1 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 1 2 1 2 1 1 2 1 2 1 2 1

That is 24 1's and 8 2's Using this information I would assume 24-1 = 23 processes were created 8 of which by the if loop but I simply can't explain it and if I should minus 1 in the first place. I would greatly appreciate some input on this thanks.

Answer 1

After the first fork, you have one parent and one child (total 2).

After the second fork, you have two parents and two children (total 4).

After the third fork, you have four parents and four children (total 8).

Each of the 4 children then forks, giving you a total of 12.

Then all the processes fork, giving 24.