get the recursive digit sum, still in review

recursive_digit_sum.cpp

long long getsuperDigit(string num, int n){
    long long sum = 0;
    string temp;
    temp.push_back(num[n]);
    sum = stoll(temp);
    if(n == 0){
        
        return sum;
    }
    return sum + getsuperDigit(num, n - 1);
}

long long getsuperHelper(long long res){
    
    string temp = to_string(res);
    long long r = res;
    cout << temp.length();
    while (temp.length() > 1) {
        
        r = getsuperDigit(temp, temp.length()- 1);
        
        
        temp = to_string(r);
        
    }
    return r;
}

int superDigit(string n, int k) {
    int r = getsuperDigit(n, n.size()- 1) * k;
    return getsuperHelper(r);
}