int* a = NULL;
int* b = *a;

b = new int(5);
std::cout << *a;
std::cout << *b;

int* a = null; //Global variable
int* b = null; //Global variable

int* returnInt(int position)
{
    switch(position)
    {
      case 0:
         return a;
      case 1:
         return b;
     }
}

some other function -

int* c = returnInt(0); // Get Global a

if (c == null)
    c = new int(5);

int* a = NULL;
int* b = *a; //here you dereference a NULL pointer, undefined behavior.

int* b = new int(5);
int*& a = b; //a is a reference to pointer to int, it is a synonym of b
std::cout << *a;
std::cout << *b;

int* b = new int(5);
int& a = *b; //a is a reference to int, it is a synonym of `*b`
std::cout << a;  //prints 5
std::cout << *b; //prints 5
a = 4;
std::cout << a;  //prints 4
std::cout << *b; //prints 4

int* b = NULL;
int*& a = b;