Create Set & Add Elements

Part of the Logic & Flow section of Coddy's C++ journey — lesson 36 of 56.

Now that you know what a set is, let's learn how to create one and add elements to it. To add elements to a std::set, you use the .insert() method.

Here's how to create an empty set and add elements:

std::set<int> numbers;
numbers.insert(5);
numbers.insert(2);
numbers.insert(8);

The most important feature of sets is that they automatically reject duplicates. If you try to insert the same value twice, the set remains unchanged:

numbers.insert(5);  // This won't add another 5
numbers.insert(5);  // Neither will this

After all these insertions, your set will only contain three unique elements: 2, 5, and 8 (automatically sorted). The duplicate attempts to insert 5 are simply ignored, which is exactly what makes sets so useful for maintaining collections of unique data.

Challenge

Easy

Create a program that demonstrates the unique element feature of std::set by adding several integers to a set, including duplicate values, and then displaying the final size to prove that duplicates are automatically ignored.

The following inputs will be provided:

An integer n representing the number of integers to insert
Then n integers to be inserted into the set

Your program should:

Create an empty std::set<int>
Read the number of integers to insert
Use a loop to read each integer and insert it into the set using the .insert() method
After all insertions, print the final size of the set using the .size() method
Print a message showing how many duplicate attempts were ignored

Use the following exact output format:

Set size: [final_size]
Duplicates ignored: [number_of_duplicates]

The number of duplicates ignored should be calculated as the difference between the total number of insertion attempts and the final size of the set. This demonstrates that sets automatically maintain uniqueness by rejecting duplicate values, which is their key feature for storing collections of unique elements.

Cheat sheet

To create a set and add elements, use .insert():

std::set<int> numbers;
numbers.insert(5);
numbers.insert(2);
numbers.insert(8);

Sets automatically reject duplicates - inserting the same value multiple times only keeps one copy:

numbers.insert(5);  // This won't add another 5
numbers.insert(5);  // Neither will this

Use .size() to get the number of unique elements in the set.

Try it yourself

#include <iostream>
#include <set>
using namespace std;

int main() {
    // Read the number of integers to insert
    int n;
    cin >> n;
    
    // Create an empty set
    set<int> mySet;
    
    // TODO: Write your code here
    // Use a loop to read n integers and insert them into the set
    // Calculate how many duplicates were ignored
    
    // Output the results
    cout << "Set size: " << mySet.size() << endl;
    cout << "Duplicates ignored: " << /* calculate duplicates */ << endl;
    
    return 0;
}