Find the Prime Number in C++ (using "cmath" library)

#include <iostream>

#include <cmath>

bool isPrime(int n) {

    if (n <= 1) return false;

    if (n <= 3) return true;

    if (n % 2 == 0 || n % 3 == 0) return false;

    for (int i = 5; i * i <= n; i += 6) {

        if (n % i == 0 || n % (i + 2) == 0) return false;

    }

    return true;

}

int main() {

    while (true) {

        int n;

        std::cout << "Enter a number (or a negative number to exit): ";

        std::cin >> n;

        if (n < 0) {

            std::cout << "Exiting...\n";

            break;

        }

        if (isPrime(n)) {

            std::cout << n << " is a prime number.\n";

        } else {

            std::cout << n << " is not a prime number.\n";

        }

        std::cout << '\n';

    }

    return 0;

}