Declaring references

Learn to declare references with &.

Declaring references

A reference is declared with the & sign: int& r = x;. Here & means 'I want a reference here'. The reference must be bound to a variable at declaration; it cannot be left empty.

After binding, r and x are the same thing. Writing std::cout << r; shows the value of x. The spacing between the type and & does not matter; int& r and int &r are equivalent.

Binding and constancy

A reference is bound to a variable at declaration and this binding stays fixed for its whole life. That is, after int& r = x;, writing r = y; does not re-bind r to y; instead, the value of y is copied into x.

This behavior can be surprising at first. Do not think of a reference as 'redirecting to another variable'; it is bound once and stays with the same target. For re-binding, you need a pointer.

Exercise Print the reference

Declare int x = 42;. Bind a reference with int& r = x;. Print r with std::cout.

Show example solution

#include <iostream>

int main() {
    int x = 42;
    int& r = x;
    std::cout << r << "\n";
    return 0;
}

Test yourself

What does this code print?
```
int x = 10;
int& r = x;
r = 20;
std::cout << x;
```
- 20
- 10
- 0
- Error
Show answer

20 — The assignment r = 20 also makes x become 20, because r is an alias for x.
Print the reference
```
std::cout << ____;
```
Show answer
```
std::cout << r;
```
Match each expression to its meaning

int& r = x

Binding
r

Alias for x
x

Original variable
42

Value

Next lesson: Reference parameters

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