Why should a function return int instead of void when it produces a result in C?

Hello Zade, really nice question.

The reason the function is defined as int instead of void is that it actually produces a value — the sum. Whenever a function calculates something and you want to use that result later in the program, the function needs a return type that matches the kind of value it gives back. In this case, the sum of natural numbers is an integer, so the function returns an int.

A void function is different. It performs an action but doesn’t hand anything back. For example, a function that only prints something to the screen doesn’t need to return a value, so void makes sense there.

So the rule is simple:
If the function gives back a value, choose a matching return type.
If it doesn’t return anything, use void.

If you have further questions, I'm here to help.