What are pointers and references in C++?

Question

Accepted Answer

**Pointer** — variable storing a memory address. **Reference** — alias for another variable.

**Pointer:**
```cpp
int x = 10;
int* ptr = &x;  // Address of x

*ptr = 20;  // Change x via pointer
std::cout << x;  // 20

// Null pointer
int* null_ptr = nullptr;

// Pointer arithmetic
int arr[] = {1, 2, 3};
int* p = arr;  // Points to arr[0]
std::cout << *(p + 1);  // 2
```

**Reference:**
```cpp
int x = 10;
int& ref = x;  // Reference to x

ref = 20;  // Change x via reference
std::cout << x;  // 20

// Reference must be initialized
// int& ref2;  // Error!
```

**Key differences:**
- Pointer can be null, reference cannot.
- Pointer can be reassigned, reference cannot.
- Pointer has its own address, reference shares address.
- Pointer arithmetic allowed, reference not.

C++: What are pointers and references in C++?