Integer to Roman Numeral converter
Helper function too complex
Your helper function and the fslt function seem too complex for what they do (helper is even recursive!).  All you are really doing is adding roman numerals starting at the highest value first.  So something like this would suffice:
#define DIM(arr)        (sizeof(arr)/sizeof(arr[0]))

void Solution::helper (int num){
    for (int i = DIM(IntVal)-1; i &gt;= 0; i--) {
        while (num &gt;= IntVal[i]) {
            output += roman[i];
            num -= IntVal[i];
        }
    }
}