Difference between i++ and (i)++ in C

int i = 3;
int j = (i)++;

vs

int i = 3;
int j = i ++;

Is there a difference between how the above two cases are evaluated?

Is the first case equivalent to incrementing an rvalue or is it undefined behaviour?

i++ and (i)++ behave identically. C 2018 6.5.1 5 says:

A parenthesized expression is a primary expression. Its type and value are identical to those of the unparenthesized expression. It is an lvalue, a function designator, or a void expression if the unparenthesized expression is, respectively, an lvalue, a function designator, or a void expression.

The wording is the same in C 1999.

In your simple example of i++ versus (i)++, there is no difference, as noted in Eric Postpischil's answer.

However, this difference is actually meaningful if you are dereferencing a pointer variable with the * operator and using the increment operator; there is a difference between *p++ and (*p)++.

The former statement dereferences the pointer and then increments the pointer itself; the latter statement dereferences the pointer then increments the dereferenced value.