LÖVE

Whats the difference between the codes above? In the second code, x is local. But in the first code, is it global or local? I think both codes is the same.

The difference is technical: global variables are stored in a globally accessible table (it's called _G and you can access it manually), and local variables are stored in Lua VM registers. For that reason, globals are accessible everywhere, but locals only accessible within the scope they were defined (file, function, block of code, etc). For the same reason, locals are faster, and are limited to 200 at a time in any given scope.

Put simply: in the second example the 'x' variable cannot be accessed outside of the file because it's local.

So x in the first code is global right?

Yes. Variables in Lua are global by default.

Global to the lua state, anyway (with löve, it may matter, since you can have multiple synchronous threads that have their own lua states), but the globals are really just keys in a table that's, by default, as raidho already said.

Here's how you can tell the difference between a global and a local.

main.lua: extra.lua: That will print 10, because x is a global, therefore it's accessible from every file in the current thread.

Now if you add this at the top of main.lua: it will print 'nil' because the second file is accessing the global variable x, which does not exist, because x is local to main.lua, and there isn't a global with that name.