Assigning and incrementing the same variable in a single expression

Answer 1

i=i++ is undefined.

Read more here: http://c-faq.com/~scs/readings/undef.950321.html

Edit: The answer to "why or why not?" is a long, unpleasant, and unsatisfying one.

Answer 2

The expression i = i++ gives undefined behaviour because you cannot assign to the same variable twice unless there is a sequence point between the assignments.

An often-cited example is the expression i=i++, which both assigns i to itself and increments i. The final value of i is ambiguous, because, depending on the language semantics, the increment may occur before or after the assignment. The definition of a particular language might specify one of the possible behaviors or simply say the behavior is undefined. In C and C++, evaluating such an expression yields undefined behavior.

Answer 3

Syntactically valid, semantically undefined, practically useless.