i = i++; is undefined. Is i = foo(i++) also undefined?

Question

For example:

int foo(int i) { return i; }

int main()
{
  int i = 0;

  i = i++;      // Undefined
  i = foo(i++); // ?

  return 0;
}

What wou

Answer 1

i = foo(i++); is fine, because i++ is executed before foo() is called. A copy of i is made, i is then incremented, then the copy is passed to foo(). It is the same as doing this explicitly:

int tmp = i++;
i = foo(tmp);