binary game part 1

#include <iostream>
#include <random>
#include <string>

int randomNumber(int);
std::string convertToBinaryString(int);


int main()
{
    std::random_device dev;
    std::mt19937 rng(dev());
    std::uniform_int_distribution<std::mt19937::result_type> dist(1, 15);
    std::string userInput;
    int iRandomNumber = 0; // current random number gets saved after function runs
    std::string sCorrectBinaryString; // current correct binary string


    while (1) {

        iRandomNumber = randomNumber(dist(rng));
        sCorrectBinaryString = convertToBinaryString(iRandomNumber);
        std::cout << iRandomNumber;
        if (iRandomNumber < 10) std::cout << " ";
        std::cout << " in Binary eingeben: ";
        std::cin >> userInput;

        if (userInput == sCorrectBinaryString) {
            std::cout << "RICHTIG" << std::endl;
        }
        else {
            std::cout << "FALSCH" << std::endl;
        }
    }
    return 0;
}

int randomNumber(int d) {

    int rN = 0;
    rN = d;
    return rN;
}

std::string convertToBinaryString(int n) {

    std::string r;
    while (n != 0) {
        r = (n % 2 == 0 ? "0" : "1") + r; n /= 2;
    }

    while (r.size() < 4) {
        r = "0" + r;
    }

    return r;

}