Sets - a practical example

Scenario: Unique Usernames for a System

Imagine you are writing a piece of software that requires a unique username for each user. You could use a set to store the usernames. When a new user tries to register, you can quickly check if the username is already taken and enforce uniqueness.

Here's a simple example in C++:

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

// Function prototype
bool addUsername(set<string>&, string);

int main() {
    set<string> usernames;

    // Try to add some usernames
    addUsername(usernames, "user1");
    addUsername(usernames, "user2");
    addUsername(usernames, "user1"); // This should fail, as "user1" is already taken

    // Output the list of usernames
    cout << "Current usernames in the system:" << endl;
    for (string user : usernames) {
        cout << user << endl;
    }

    return 0;
}

// Function implementation
bool addUsername(set<string>& usernames, string username) {
    //The insert method returns a pair, where the second
    //element is a boolean that is true if the insert was
    //successful (the username was unique) and false otherwise.
    auto result = usernames.insert(username);
    if (!result.second) {
        cout << "Username '" << username << "' is already taken." << endl;
        return false;
    } else {
        cout << "Username '" << username << "' has been added." << endl;
        return true;
    }
}

In this example, the addUsername function checks if the username is already in the set. If it is not, it adds the new username; otherwise, it informs that the username is taken. The set automatically ensures that all usernames are unique.

This is a practical use case for a set because:

You need to ensure that each element (username) is unique.
You want to have quick lookups to check if an element already exists in the set.