Do all programs have to have a return value?

Question

I am currently writing my own programming language, mainly for educational purposes.

When writing a simple hello world example, I realised that many programming languages take the following form:

write "hello world" to the console
return 0

• Do all programs have to return an integer somehow?
• Do those that don't explicitly require you to state a return value implicitly return 0 anyway?
• Does this change between popular operating systems based upon Windows NT, Linux Kernel or Mac OS Xs kernel?
• If so, why?

I am unsure what to tag this question as, any help is appreciated of course.

Answer 1

It's a OS specific question, so no-one can answer if it's true for all OS. That said, I believe that, in any reasonable OS, yes - a program has to have a return value.

Why? To chain the programs execution and therefore to report problems, relaunch and so on. There aren't programs that don't return a value, it's just a compiler that hides it from a programmer.

Is this the case on all major operating systems? Probably. 0 usually means means success but you shouldn't make such assumptions when writing your programs; use language constants.

If you write your own language you may map your error codes (exceptions, termination reasons) to the host language's error codes.