A reference is an alias, that is, another name for an already existing variable. Once a reference is initialized to a variable, it cannot be changed to refer to another variable.

Recommended over pointers for function parameters and return values when the object is known to exist. It provides a cleaner syntax and is safer as it cannot be nullptr.

• Access: $O(1)$

cpp Standard
int x = 10;
int &ref = x; // ref is an alias for x

ref = 20; // x is now 20

• Trying to declare a reference without initializing it.
• Returning a reference to a local variable (Dangling reference).
• Thinking you can "re-seat" a reference to point to another variable after initialization.