Pointer arithmetic
- C++ course
- Beginner
- Lesson 81/116
- 5 min
Learn to do arithmetic on pointers with + and -.
Pointer arithmetic
Pointers support arithmetic with + and -. Adding +1 to a pointer moves it to the next element; it steps by the size of the type. For example, on an int* p, p + 1 moves p by one int size.
This is useful for walking arrays. An array's name is the address of its first element; you can start with int* p = arr; and reach elements with *(p + 1), *(p + 2). This is the same as writing arr[1].
Array and pointer connection
An array's name is interpreted as the address of its first element. arr and &arr[0] mean the same. So you can write int* p = arr;; p now points to the start of the array.
arr[i] is actually a shortcut for *(arr + i). So indexing is a combination of pointer arithmetic and dereference. This connection reflects the low-level nature of C++; but in everyday code, writing arr[i] is more readable.
Practice Walk an array with a pointer
Declare int arr[] = {10, 20, 30};. Bind p to the start of the array with int* p = arr;. Print the second element using *(p + 1) with std::cout.
Starter code
#include <iostream>
int main() {
// Declare the array
// Bind p to the array
// Print the second element
return 0;
}Sample solution
#include <iostream>
int main() {
int arr[] = {10, 20, 30};
int* p = arr;
std::cout << *(p + 1) << "\n";
return 0;
}Expected output
20
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does this code print?
int arr[] = {10, 20, 30};
int* p = arr;
std::cout << *(p + 1);- 10
- 20 Correct answer
- 0
- 30
Explanation: *(p + 1) gives the second element of the array, which is 20.
2 Match each expression to its meaning
| Term | Meaning |
|---|---|
p + 1 |
Next element |
*(p + 1) |
Second value |
arr |
Array name |
int* p = arr |
Binding |
3 Pointer arithmetic
std::cout << *(p ____ 1);std::cout << *(p + 1);Explanation: *(p + 1) accesses the element after p.