Hey there! Today, we're exploring sets in C++ — a useful way to handle collections of unique items. By the end of this lesson, you’ll know how to define sets, add and remove items, check for specific items, and iterate through all the items in a set. Let's dive in!

A set in C++ is a container holding unique elements, just like a stamp collection without duplicates. Sets are perfect for tracking unique items without worrying about duplicates — like a class attendance list ensuring no name repeats.

To use sets in C++, include the set library with this line:

C++
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1#include <set>

To create an empty set that stores integers, define it like this:

C++
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1#include <set>
2
3std::set<int> mySet;

This declares a set named mySet for integers.

Add elements using the insert function:

C++
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1#include <set>
2#include <iostream>
3
4int main() {
5    std::set<int> mySet;
6
7    mySet.insert(10);
8    mySet.insert(20);
9    mySet.insert(30);
10
11    return 0;
12}

If you try to insert 10 again, it won't be added as it’s a duplicate.

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1mySet.insert(10); // Duplicate, won't be added

However, it won't cause any errors.

Remove an item with the erase function:

C++
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1#include <set>
2#include <iostream>
3
4int main() {
5    std::set<int> mySet;
6
7    mySet.insert(10);
8    mySet.insert(20);
9    mySet.insert(30);
10
11    // Remove element 20
12    mySet.erase(20);
13
14    return 0;
15}

Use find to check if an element is in the set. Find is a complex function that returns a thing called iterator pointing to the set's element. We will cover the details of it in the "Intermediate Programming in C++" path. By now, let's just say that if the find method doesn't find the element, it returns a thing which is equal to set.end(), so here is how we can make the comparison:

C++
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1#include <set>
2#include <iostream>
3
4int main() {
5    std::set<int> mySet;
6
7    mySet.insert(10);
8    mySet.insert(20);
9    mySet.insert(30);
10
11    // Check if 10 is in the set
12    if (mySet.find(10) != mySet.end()) {
13        std::cout << "10 is in the set" << std::endl;  // Output: 10 is in the set
14    }
15
16    return 0;
17}

It works, but seems a bit tricky and hard to remember, right? Let's try out another approach!

Alternatively, use the count function:

C++
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1#include <set>
2#include <iostream>
3
4int main() {
5    std::set<int> mySet;
6
7    mySet.insert(10);
8    mySet.insert(20);
9    mySet.insert(30);
10
11    // Check if 20 is in the set
12    if (mySet.count(20) > 0) {
13        std::cout << "20 is in the set" << std::endl;  // Output: 20 is in the set
14    }
15
16    return 0;
17}

The set can only have one instance of each element, so .count will always return either 0 or 1.

Finally, we can iterate the set using a range-based for loop:

C++
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1#include <set>
2#include <iostream>
3
4int main() {
5    std::set<int> mySet;
6
7    mySet.insert(20);
8    mySet.insert(10);
9    mySet.insert(30);
10
11    // Print all elements
12    for (int item : mySet) {
13        std::cout << item << " ";  // Output: 10 20 30 
14    }
15
16    return 0;
17}

This code prints: 10 20 30 . Note that the set always stores elements in the ascending order. The order of adding elements to the set doesn't matter.

Great job! Here’s what we learned:

• Sets store unique elements in a specific order.
• Include the <set> header to use sets.
• Define, add, remove, and check elements in a set using insert, erase, find, and count.
• Use iterators to loop through set elements.

Sets are great for handling collections of unique items efficiently.

Now, let's practice! You'll define your own sets, add and remove elements, and check for item existence. Ready? Let's start practicing on CodeSignal!