504. Base 7

https://leetcode.com/problems/base-7/description/
Solution 1.
    string convertToBase7(int num) {
        if(num == 0) return "0";
        string res;
        int x = abs(num);
        while(x) {
            res = to_string(x % 7) + res;
            x /= 7;
        }
        return (num>0 ? "":"-")+res;
    }