What is the difference between a pointer variable and a reference variable?

 

Pointer variables and reference variables are both used in programming to work with memory addresses, but they have some key differences. Here's an explanation with examples in C++:

1. Pointer Variables:

   • A pointer variable stores the memory address of another variable.
   • Pointers can be reassigned to point to different memory locations.
   • Pointers can be null, which means they don't point to any valid memory location.
   • They are declared using an asterisk (*) before the variable name.

cpp

#include <iostream>

int main() {
    int x = 10;
    int* ptr = &x; // Declare and initialize a pointer to an int

    std::cout << "Value of x: " << x << std::endl;
    std::cout << "Value pointed to by ptr: " << *ptr << std::endl;

    // Change the value of x indirectly through the pointer
    *ptr = 20;
    std::cout << "New value of x: " << x << std::endl;

    return 0;
}

2. Reference Variables:

   • A reference variable is an alias or another name for an existing variable.
   • Once a reference is established, it cannot be changed to refer to another variable.
   • References must be initialized at the time of declaration, and they cannot be null.
   • They are declared using an ampersand (&) before the variable name.

cpp

#include <iostream>

int main() {
    int x = 10;
    int& ref = x; // Declare and initialize a reference to an int

    std::cout << "Value of x: " << x << std::endl;
    std::cout << "Value referred to by ref: " << ref << std::endl;

    // Change the value of x directly through the reference
    ref = 20;
    std::cout << "New value of x: " << x << std::endl;

    return 0;
}

In the above examples, ptr is a pointer variable that can change where it points, and ref is a reference variable that is bound to x and cannot be changed to refer to another variable. Changes made through the pointer affect the original variable x, while changes made through the reference also affect x.