diff --git a/content/cpp/concepts/deque/terms/at/at.md b/content/cpp/concepts/deque/terms/at/at.md new file mode 100644 index 00000000000..8082b9e0a2e --- /dev/null +++ b/content/cpp/concepts/deque/terms/at/at.md @@ -0,0 +1,130 @@ +--- +Title: '.at()' +Description: 'Accesses an element at a specified index in a deque with bounds checking.' +Subjects: + - 'Computer Science' + - 'Game Development' +Tags: + - 'Containers' + - 'Deques' + - 'Methods' + - 'STL' +CatalogContent: + - 'learn-c-plus-plus' + - 'paths/computer-science' +--- + +The C++ **`.at()`** [function](https://www.codecademy.com/resources/docs/cpp/functions) accesses the element at a given index in a deque while performing bounds checking. If the index is out of range, the function throws an `std::out_of_range` [exception](https://www.codecademy.com/resources/docs/cpp/exceptions). This makes it a safer alternative to the subscript operator `[]`, which offers no safety checks. + +## Syntax + +```pseudo +deque.at(pos) +``` + +**Parameters:** + +- `pos`: A zero-based index of the element to access. Must be within the valid range of the deque. + +**Return value:** + +Returns a reference to the element at the given position. + +**Exceptions:** + +Throws `std::out_of_range` if `pos` is invalid. + +## Example 1: Accessing Elements Safely + +In this example, `.at()` retrieves elements from valid positions in the deque: + +```cpp +#include +#include +using namespace std; + +int main() { + deque numbers = {10, 20, 30, 40}; + + cout << "Element at index 2: " << numbers.at(2) << endl; + cout << "Element at index 0: " << numbers.at(0) << endl; + + return 0; +} +``` + +The output of this code is: + +```shell +Element at index 2: 30 +Element at index 0: 10 +``` + +The `.at()` function returns elements at positions 2 and 0 with built-in bounds checking. + +## Example 2: Handling Out-of-Range Access + +In this example, accessing index 5 triggers an exception because the index is outside the deque's valid range: + +```cpp +#include +#include +using namespace std; + +int main() { + deque names = {"Ava", "Mira", "Leo"}; + + try { + cout << names.at(5) << endl; + } catch (const out_of_range& e) { + cout << "Error: " << e.what() << endl; + } + + return 0; +} +``` + +The output of this code is: + +```shell +Error: deque::_M_range_check: __n (which is 5)>= this->size() (which is 3) +``` + +## Codebyte Example + +This example demonstrates safe element access and shows how `.at()` behaves when an invalid index is used: + +```codebyte/cpp +#include +#include +using namespace std; + +int main() { + deque letters = {'A', 'B', 'C', 'D'}; + + cout << "First element: " << letters.at(0) << endl; + cout << "Third element: " << letters.at(2) << endl; + + try { + cout << letters.at(10) << endl; + } catch (const out_of_range& e) { + cout << "Caught exception: " << e.what() << endl; + } + + return 0; +} +``` + +## Frequently Asked Questions + +### 1. What is the use of deque in C++? + +A deque (double-ended queue) stores elements in a dynamic sequence where insertions and deletions at both the front and back are efficient. It supports random access like a vector but provides faster operations at the beginning of the structure. + +### 2. What is a std::deque? + +`std::deque` is a standard container that provides a dynamic array-like structure with fast operations at both ends. It is implemented as segmented memory blocks, which allows it to grow without relocating all elements like a vector. + +### 3. How to check if deque is empty in C++? + +A deque can be checked for emptiness using the `.empty()` method, which returns `true` if it contains no elements and `false` otherwise. This check is constant time and works for all standard containers.