The idiomatic way to get a pointer to one past the end of an array x with element-type foo is

    x + sizeof x / sizeof *x

which is equivalent to

    (foo *)((char *)x + sizeof x)

whereas

    x + sizeof x

is equivalent to

    (foo *)((char *)x + sizeof (foo) * sizeof x))

The expression

    &x + 1

is not idiomatic as it has the type pointer-to-array-of-foo instead of pointer-to-foo.

As to your final question: Parameter declarations discard the size of array types - they are actually pointer-declarations in disguise.

To enforce a fixed array size, you need to declare a parameter of type pointer-to-array, eg

    void bar(int (*arg)[42]);

which you'd have to call like this:

    int x[42] = { 0 };
    bar(&x);