> Does it help to say
>
>   M-: (eval (c-align-cpp-indent-to-body))
             ^
             '

The quote is of the essence, otherwise you're asking to evaluate the
return value of the expression.

And since the above expression was wrong (it lacked the let binding),
what he should do is either

    M-: (eval '(let ((c-syntactic-context (c-guess-basic-syntax))))
                 (c-align-cpp-indent-to-body)) RET

or use `(defvar c-syntactic-context nil)` somewhere, or

    M-: (progn (defvar c-syntactic-context)
               (let ((c-syntactic-context (c-guess-basic-syntax))))
                 (c-align-cpp-indent-to-body)) RET

or write the `(let ((c-syntactic-context (c-guess-basic-syntax))))
(c-align-cpp-indent-to-body))` inside `cc-cmds.el` or `cc-vars.el`
and use `C-x C-e` there.

or ...


        Stefan