In C++, a reference variable is an alias to another variable. Once a reference is initialized with a variable, it can be used to refer to that variable. To create a reference variable, we use the ampersand (&) symbol.

Here's an example of creating a reference variable:

int main() {
    int x = 5;
    int& ref = x;

    cout << x << endl;   // Output: 5
    cout << ref << endl; // Output: 5

    return 0;
}

In this example, we create an integer variable x and initialize it to 5. Then we create a reference variable ref and initialize it with x using the ampersand (&) symbol. Now ref is an alias for x.

We can use ref to modify the value of x, like so:

int main() {
    int x = 5;
    int& ref = x;

    ref = 10;

    cout << x << endl;   // Output: 10
    cout << ref << endl; // Output: 10

    return 0;
}

In this example, we assign ref the value 10, which modifies the value of x as well.