How do you declare a reference in C++?

Type& name = variable; creates an alias — a second name for an existing variable.

* A reference is the object under another name (must be bound at birth, never reseated, never null); a pointer merely holds its address. *

int x = 10;
int& ref = x;    // ref is now another name for x

ref = 20;        // changes x to 20
cout << x;       // prints 20

Key differences from pointers:

Common use — pass by reference:

void swap(int& a, int& b) {
    int temp = a;
    a = b;
    b = temp;
}

Tip: A reference is like a pointer that's always valid and auto-dereferenced — cleaner to use, but less flexible (you can't reseat it or make it null).

Go deeper:

• Reference declaration — cppreference — lvalue and rvalue reference rules.
• Reference (C++) — Wikipedia — references contrasted with pointers.