Difference between pointers and references in C++ v2

// Pointers and references syntax
int x = 5;
int& y = x; // y == x
y++; // y == 6 && x == 6
int * z = &x; // z is address of x
int * zz = &y; // z == zz && *z == *zz && *z == 6 && *z == x && *z == y
(*zz)++; //  x == 7 && *z == 7 etc.


// References
int x = 5, y = 10;
int& z = x;
z = y;
++y;
// z == 10 && x == 10 && y == 11

// Pointers are nullable
int * x = NULL; // OK
int& x = NULL; // does not compile

// Const modifiers
int * x0; // pointer to int
++x0; // OK
++(*x0); // OK

const int * x1; // pointer to constant int
int const * x2; // same thing
++x1; // OK
++(*x1) // FAIL

int * const x3; // constant pointer to int
++x3; // FAIL
++(*x3); // OK

const int * const x4; // constant pointer to constant int
int const * const x5; // same thing
++x4; // FAIL
++(*x4); // FAIL

const int const * xx; // should not compile

int & x6; // reference to int
const int & x7; // reference to constant int
int & const x8; // this doesn't make sense, I'm not sure that it compiles