[Term Entry] C++ Unordered-sets: size() Contribution

content/cpp/concepts/unordered-set/terms/size/size.md

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+---
+Title: 'size()'
+Description: 'Returns the number of elements currently stored in the unordered set.'
+Subjects:
+  - 'Code Foundations'
+  - 'Computer Science'
+Tags:
+  - 'Containers'
+  - 'Methods'
+  - 'Sets'
+  - 'STL'
+CatalogContent:
+  - 'learn-c-plus-plus'
+  - 'paths/computer-science'
+---
+
+The **`size()`** member [function](https://www.codecademy.com/resources/docs/cpp/functions) of `unordered_set` is used to return the number of elements currently stored in the container as a `size_type`. If the `unordered_set` is empty, it returns `0`.
+
+## Syntax
+
+```pseudo
+set_name.size();
+```
+
+**Parameters:**
+
+This function takes no parameters.
+
+**Return value:**
+
+Returns a `size_type` value representing the number of elements in the `unordered_set`.
+
+## Example 1: Basic Usage of `size()`
+
+In this example, the program inserts one element into an `unordered_set` and prints its size:
+
+```cpp
+#include <iostream>
+#include <unordered_set>
+using namespace std;
+
+int main() {
+  unordered_set<int> mySet;
+  mySet.insert(10);
+
+  cout << "Size: " << mySet.size();
+  return 0;
+}
+```
+
+The output of this code is:
+
+```shell
+Size: 1
+```
+
+## Example 2: Counting Unique Elements
+
+In this example, the program initializes an `unordered_set` with integers (including duplicates), prints its size, and displays its elements:
+
+```cpp
+#include <iostream>
+#include <unordered_set>
+using namespace std;
+
+int main() {
+  unordered_set<int> mySet {1, 2, 3, 3, 1, 3, 2, 4, 5, 7};
+
+  cout << "There are " << mySet.size() << " elements.\n";
+  cout << "The elements are: ";
+  for (int ele : mySet) {
+    cout << ele << " ";
+  }
+  return 0;
+}
+```
+
+The output of this code is:
+
+```shell
+There are 6 elements.
+The elements are: 7 5 4 3 2 1
+```
+
+> **Note:** The order of elements may vary.
+
+Since an `unordered_set` cannot contain duplicates, the code returns `6` as its size and only the unique elements in the container.
+
+## Codebyte Example
+
+In this example, the program compares `size()` with `sizeof()` to show that element count and memory footprint are unrelated:
+
+```codebyte/cpp
+#include <iostream>
+#include <unordered_set>
+using namespace std;
+
+int main() {
+  unordered_set<int> mySet;
+
+  for (int i = 0; i < 10; i++) {
+    mySet.insert(i);
+  }
+
+  cout << "Number of elements: " << mySet.size() << "\n";
+  cout << "The set's byte usage: " << sizeof(mySet);
+  return 0;
+}
+```
+
+`size()` returns the number of stored elements, while `sizeof()` returns the memory footprint of the container object, which does not grow with element count.