Variables and Memory

Every variable lives somewhere in your computer's memory, and C++ is unusual among popular languages in letting you work with that memory directly.

Declaring variables

int xp = 100;         // an integer variable holding the value 100
double price = 9.99;  // a floating-point number
char grade = 'A';     // a single character
bool passed = true;   // true or false

Every variable in C++ has a fixed type decided when it's declared, an int can never later hold a decimal or a piece of text.

Addresses, pointers, and references

Every variable lives at a specific address in memory, think of memory as a huge street of numbered houses, a variable's address is just its house number.

int xp = 100;
std::cout << &xp;      // prints xp's address, e.g. 0x7ffc3a2b1c

int* ptr = &xp;        // ptr is a pointer: it stores xp's address
std::cout << *ptr;     // *ptr "dereferences" ptr: prints 100, the value at that address

int& ref = xp;         // ref is a reference: another name for xp itself
ref = 200;             // this actually changes xp too!
std::cout << xp;       // prints 200

Pointers vs. references

• A pointer is a variable that stores an address, it can be reassigned to point somewhere else, or set to nullptr to point at nothing at all.
• A reference is an alias for an existing variable, it must be bound to something when it's created, and can never be changed to refer to something else afterward.