Mine

void ultoa(unsigned long l, char* pStr, int base)
{
        //not taking hex (0-F) into consideration
        //given specified range was 0<=base<=16
        if(l < base)
        {
                *pStr + l;
        }
        else
        {
                *pStr = ultoa(l/base, *pStr, base) + (l%base);
        }

}