Integer to Roman -- Leetcode

Question:

Given an integer, convert it to a roman numeral.

Input is guaranteed to be within the range from 1 to 3999.

Answer:
Using greedy algorithm. Simple solution is to list all elements, then num minus the largest element every time on each digit position.

class Solution {
public:
    string intToRoman(int num) {
        string str;  
        string symbol[]={"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"};  
        int value[]=    {1000, 900, 500, 400, 100,  90,  50,  40,  10, 9,  5,  4,  1};  
        for(int i=0;num!=0;++i) {
            while(num>=value[i]) {
             
                num-=value[i];
                str+=symbol[i];
            }
        }
        return str;
    }
};