[leetcode]405. Convert a Number to Hexadecimal

题目链接：https://leetcode.com/problems/convert-a-number-to-hexadecimal/

Given an integer, write an algorithm to convert it to hexadecimal. For negative integer, two’s complement method is used.

Note:

All letters in hexadecimal (a-f) must be in lowercase.
The hexadecimal string must not contain extra leading 0s. If the number is zero, it is represented by a single zero character '0'; otherwise, the first character in the hexadecimal string will not be the zero character.
The given number is guaranteed to fit within the range of a 32-bit signed integer.
You must not use any method provided by the library which converts/formats the number to hex directly.
Example 1:

Input:
26

Output:
"1a"
Example 2:

Input:
-1

Output:
"ffffffff"

class Solution{
        public:
                string toHex(int num)
                {
                        while(num>0)
                        {
                                hexString=hexChar[num & 0xF]+hexString;
                                num=(unsigned)num>>4;
                        }
                        return hexString.empty()?"0":hexString;

                }
        private:

                string hexString="";
                string hexChar="0123456789abcdef";
};