How to create two processes ~~~~~~

How to create two processes ~~~~~~ -- Linux general technology-Linux programming and kernel information. The following is a detailed description. Oh, sorry again...
I read a book where the parent process creates two sub-processes, which are written as follows:
Int main ()
{
Pid_t p = fork ();
Pid_t q = fork ();
Switch (p ){.......}
Switch (q ){.......}
}
I think there is a problem with this writing. I understand that the process created by q has not only been created in the parent process main, but also in the process created by p. In this case, there should be four process spaces: p in main, q in main, q in p.
So I think if we want to create two sub-processes with the same status in a parent process, we should write this:
Int main ()
{
Pid_t p = fork ();
If (p> 0)
{
Pid_t q = fork ();
Switch (q ){.......}
}
}
In this way, the parent processes of p and q2 are both main and have the same status.
I don't know if I understand this, right ???