How are arguments passed into functions in Elisp?

Coming from a C++ background, I'm trying to figure out how arguments are passed into methods in Elisp. While I acknowledge that maybe the wording could be different, I'm wondering if it is closer to the C++ idea of passing by reference or passing by value? If I alter the parameter in the method itself, will it alter the parameter that was passed in in the function call?

Solution

All Lisps (Emacs Lisp, Common Lisp) pass parameters by value, always:

(defparameter x 42)  ; defconst in Emacs Lisp
(defun test (x)
  (setq x 10))
(test x)
==> 10
x
==> 42

Note, however, that some values are actually pointers (or, rather, objects with components), so a function can modify their content by side effects:

(defparameter x (list 1 2))
(defun test (x)
  (setf (first x) 42
        (second x) 24
        x 17))
(test x)
==> 17
x
==> (42 24)

PS1. Cf. When to use ' (or quote) in Lisp? -- "quoted arguments" are evaluated too: the evaluation strips the quote.

PS2. Cf. add-to-list - it accepts a symbol (variable name) and modifies its value. This only works for global dynamic variables, not for lexical variables. Not a very good idea.