C++ Pointers

Memory Addresses

Every variable is stored at a memory address. Use the address-of operator & to get it:

#include <iostream>
using namespace std;

int main() {
    int x = 42;
    cout << "Value:   " << x  << endl;
    cout << "Address: " << &x << endl;
    return 0;
}

Output (addresses vary):

Value:   42
Address: 0x7ffee4b2a8bc

Pointer Variables

A pointer stores a memory address. Declare with type*:

int  x = 42;
int* ptr = &x;    // ptr holds the address of x

cout << ptr;      // prints address (same as &x)
cout << *ptr;     // prints 42 (value AT the address)

Dereferencing

Use * to access the value at the address a pointer holds:

int x = 10;
int* ptr = &x;

*ptr = 99;          // change x through the pointer
cout << x;          // 99

#include <iostream>
using namespace std;

int main() {
    double price = 29.99;
    double* p = &price;

    cout << "Price: $" << *p  << endl;   // 29.99
    *p = 19.99;
    cout << "Sale:  $" << price << endl;  // 19.99
    return 0;
}

Null Pointers

A pointer that points to nothing should be set to nullptr (C++11):

int* p = nullptr;   // safe — not pointing to garbage

if (p == nullptr) {
    cout << "Pointer is null" << endl;
}

#include <iostream>
using namespace std;

int main() {
    int num = 15;
    int* ptr = &num;

    *ptr = *ptr * 2;

    cout << "Via variable: " << num  << endl;   // 30
    cout << "Via pointer:  " << *ptr << endl;   // 30
    return 0;
}

Summary

• &variable returns the memory address of a variable.
• type* ptr declares a pointer that stores an address.
• *ptr dereferences — accesses the value at the stored address.
• Always initialize pointers; use nullptr for "no address".