Full concept of return(0), return

Question

I'm confused this concept

Answer 1

Returns data from a function to whatever called it. In the case of the main loop, it's returning you to your OS and can provide some form of a status / error (if necessary).

To put it simply, what do you want a function to -return- to you. If you allow it to return data to you, then you can use the results where you originally called it from.