Rules for references

  int k = 3;
  double a = 5.0;
  double &d = a;
  void f(int &i, double &d);
  f(k,a);

A reference must be initialized when declared
A reference is constant by nature
- Once established the reference can never be set to reference something else
No operator operates on a reference as such - only the object referenced
There is no null reference (in the sense that there is a nullptr)
Pointers to references and arrays of references do not exist
- But references to pointers and references to array can exists