I have to solve the following problem in C++ and I have no idea how to do this...
"A parent process sends an array of numbers to another process (son). The son must count the prime numbers from the array and send back the result. The GUI of the parent consists of a textbox to get the array of numbers, a button to send data to the son and a label to show the result."
What are you having a problem with, the GUI or the prime numbers?
For the GUI you could use Qt or wxWidgets or something. There are a lot of option for GUI development.
For the prime numbers, just pass the array into a function and test each number for prime, then return a count of the primes.
If you post what you have we can help more.