difference between pointer and reference

//Passing by Pointer://

// C++ program to swap two numbers using 
// pass by pointer. 
#include <iostream> 
using namespace std; 
  
void swap(int* x, int* y) 
{ 
    int z = *x; 
    *x = *y; 
    *y = z; 
} 
  
int main() 
{ 
    int a = 45, b = 35; 
    cout << "Before Swap\n"; 
    cout << "a = " << a << " b = " << b << "\n"; 
  
    swap(&a, &b); 
  
    cout << "After Swap with pass by pointer\n"; 
    cout << "a = " << a << " b = " << b << "\n"; 
} 
o/p:
Before Swap
a = 45 b = 35
After Swap with pass by pointer
a = 35 b = 45

//Passing by Reference://

// C++ program to swap two numbers using 
// pass by reference. 
  
#include <iostream> 
using namespace std; 
void swap(int& x, int& y) 
{ 
    int z = x; 
    x = y; 
    y = z; 
} 
  
int main() 
{ 
    int a = 45, b = 35; 
    cout << "Before Swap\n"; 
    cout << "a = " << a << " b = " << b << "\n"; 
  
    swap(a, b); 
  
    cout << "After Swap with pass by reference\n"; 
    cout << "a = " << a << " b = " << b << "\n"; 
} 
o/p:
Before Swap
a = 45 b = 35
After Swap with pass by reference
a = 35 b = 45

//Difference in Reference variable and pointer variable//

References are generally implemented using pointers. A reference is same object, just with a different name and reference must refer to an object. Since references can’t be NULL, they are safer to use.

A pointer can be re-assigned while reference cannot, and must be assigned at initialization only.
Pointer can be assigned NULL directly, whereas reference cannot.
Pointers can iterate over an array, we can use ++ to go to the next item that a pointer is pointing to.
A pointer is a variable that holds a memory address. A reference has the same memory address as the item it references.
A pointer to a class/struct uses ‘->'(arrow operator) to access it’s members whereas a reference uses a ‘.'(dot operator)
A pointer needs to be dereferenced with * to access the memory location it points to, whereas a reference can be used directly.