docs(cpp/deque): add .back() term entry

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

@@ -0,0 +1,81 @@
+---
+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 of a deque. It can be used to read or modify that element without removing it from the container.
+
+> **Note:** Calling `.back()` on an empty deque results in undefined behavior. Use `.empty()` to check before accessing elements.
+
+## 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
+
+The following example accesses the last element in a deque and then modifies it via the reference returned by `.back()`:
+
+```cpp
+#include <deque>
+#include <iostream>
+
+int main() {
+  std::deque<int> values = {10, 20, 30};
+
+  std::cout << "Back: " << values.back() << std::endl;
+
+  // Modify the last element through the reference returned by .back()
+  values.back() = 99;
+  std::cout << "Back after modification: " << values.back() << std::endl;
+
+  return 0;
+}
+```
+
+This program produces the following output:
+
+```shell
+Back: 30
+Back after modification: 99
+```
+
+## Codebyte Example
+
+This example demonstrates reading and modifying the last element of a deque using `.back()`:
+
+```codebyte/cpp
+#include <deque>
+#include <iostream>
+
+int main() {
+  std::deque<std::string> words = {"alpha", "beta", "gamma"};
+
+  std::cout << words.back() << std::endl; // Prints the last element
+
+  words.back() = "omega";                 // Modify the last element
+  std::cout << words.back() << std::endl; // Prints the modified value
+
+  return 0;
+}
+```