conversion to roman number

string convertToRoman(int num) {

  int decNum = [ 1, 4, 5, 9, 10, 40, 50, 90, 100, 400, 500, 900, 1000 ];
  string romNum = [ 'I', 'IV', 'V', 'IX', 'X', 'XL', 'L', 'XC', 'C', 'CD', 'D', 'CM', 'M' ];
  string romanNum = "";

  while (num > 0){
      int i = 0;
      while(num >= decNum[i+1]){
            i++;
      }
      romanNum += romNum[i];
      num -= decNum[i];
  }
  return romanNum;

}