405. 数字转换为十六进制数

链接：405. 数字转换为十六进制数

题解：

力扣

class Solution {
public:
    string toHex(int _num) {
        if (_num == 0) {
            return "0";
        }
        std::string res;
        long num = _num;
        if (num < 0) {
            num = pow(2, 32) + num;
        }
        while (num > 0) {
            int val = num % 16;
            char c = val + '0';
            if (val >= 10) {
                c = val - 10 + 'a';
            }
            res.push_back(c);
            num = num/16;
        }
        reverse(res.begin(), res.end());
        return res;
    }
};