Confusion with syntax for postfix expressions and operators

Question

In the following case,

int i = 0;
int j = 42;
i = j++;

I know ++ is posfix operator, So, is j a posfix expression or should you say j++ is posfix expression ?

Answer 1

Syntactically, both j and j++ are postfix-expressions.

See the grammar in section 5.2 of the C++ 2003 standard:

postfix-expression:
    primary-expression
    ...
    postfix-expression ++

( j is also a primary-expression; j++ is not.)

The fact that a primary-expression is a kind of postfix-expression (even if it doesn't contain a postfix operator) is mostly a matter of convenience for defining the language syntax. There's not much point in referring to j as a postfix-expression unless you're talking about parsing C++ (or C) source code.