To clarify, a bit, system does do a fork and exec to run the program you specify, but it also waits for that program to complete before returning control back to your code. This means that you cannot use system() to (directly) get 4 processes running at the same time, and that you cannot try to keep track of let alone control the processes created by system(), because these processes are gone by the time your program starts running again.

You already have a reply from blakem which provides a piece of code demonstrating the use of fork & exec. If you'd like more info, doing a Super Search for nodes containing 'fork' and 'exec' in the text comes up with a lot of useful looking hits.