Base-7.cpp

class Solution
{
  public:
    string convertToBase7(int num)
    {
        if (num == 0)
            return "0";

        string ans;
        bool isNeg = num < 0;

        num = abs(num);
        while (num > 0)
        {
            ans.append(to_string(num % 7));
            num /= 7;
        };
        reverse(ans.begin(), ans.end());
        if (isNeg)
            ans = "-" + ans;
        return ans;
    }
};