[Term Entry] C++ Deque : back() (#7893)

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* [Term Entry] C++ Deque : back()

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Author: mamtawardhani

content/cpp/concepts/deque/terms/back/back.md

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+---
+Title: '.back()'
+Description: 'Returns a reference to the last element in the deque.'
+Subjects:
+  - 'Computer Science'
+  - 'Game Development'
+Tags:
+  - 'Containers'
+  - 'Data Structures'
+  - 'Deques'
+  - 'Methods'
+CatalogContent:
+  - 'learn-c-plus-plus'
+  - 'paths/computer-science'
+---
+
+In C++, the **`.back()`** [method](https://www.codecademy.com/resources/docs/cpp/methods) returns a reference to the last element in a [deque](https://www.codecademy.com/resources/docs/cpp/deque). It allows direct access to that element for reading or modifying without removing it.
+
+> **Note:** Calling `.back()` on an empty deque leads to undefined behavior. Check with [`.empty()`](https://www.codecademy.com/resources/docs/cpp/deque/empty) before using `.back()`.
+
+## Syntax
+
+```pseudo
+dequeName.back();
+```
+
+**Parameters:**
+
+This method does not take any parameters.
+
+**Return value:**
+
+Returns a reference to the last element of the deque. If the deque is `const`, it returns a `const` reference.
+
+## Example: Accessing and Updating the Last Element
+
+This example retrieves the last number in a deque, updates it, and displays the change:
+
+```cpp
+#include <deque>
+#include <iostream>
+
+int main() {
+  std::deque<int> scores = {45, 67, 89};
+
+  std::cout << "Last score: " << scores.back() << std::endl;
+
+  // Update the last element
+  scores.back() = 100;
+
+  std::cout << "Updated last score: " << scores.back() << std::endl;
+  return 0;
+}
+```
+
+This program produces the following output:
+
+```shell
+Last score: 89
+Updated last score: 100
+```
+
+## Codebyte Example: Using `.back()` in a Conditional Check
+
+This example shows how `.back()` can be used to verify or modify the final value in a deque:
+
+```codebyte/cpp
+#include <deque>
+#include <iostream>
+
+int main() {
+  std::deque<std::string> tasks = {"plan", "write", "review"};
+
+  if (tasks.back() == "review") {
+    tasks.back() = "submit"; // Update the last task
+  }
+
+  std::cout << "Final task: " << tasks.back() << std::endl;
+  return 0;
+}
+```