a.  px is the pointer to x

    *px dereferences this pointer, giving us 10 (= the value x)

    (*px)++ is 10 + 1, which is 11

    so x = 11, but since this is a post-fix operation, z is still 10

 

b.  *py dereferences the pointer py, giving us 20 (= the value of y)

     *py + y is 20 + 20, which is 40

     so z = 40

 

c.   x and y are integers, and an int cannot be dereferenced.