RPN updated version

rpn.cpp

#define _PREP_AOP_ { if (args.size() < 2) return i + 1; arg2 = args.top(); args.pop(); arg1 = args.top(); args.pop(); }
#define _CHECK_ADD_RES_ { if (args.top() - arg2 != arg1) return i + 1; }
#define _CHECK_SUB_RES_ { if (args.top() + arg2 != arg1) return i + 1; }
#define _CHECK_MUL_ARG_ { if (arg2 != 0 && arg1 > LONG_MAX / arg2) return i + 1; }
#define _CHECK_DIV_ARG_ { if (arg2 == 0 || (arg1 == LONG_MIN && arg2 == -1)) return i + 1; }

int RPN(char *str, int rdx, long &res)
{
  if (str == NULL || str[0] == NULL)
    return false;

  stack<long> args;    
  long arg1;
  long arg2;
  long num;

  for (size_t i = 0; str[i] != 0; ++i)
  {
    switch(str[i])
    {
      case ' ':
          continue;
        break;

      case '+':
          _PREP_AOP_;
          args.push(arg1 + arg2);
          _CHECK_ADD_RES_;
        break;

      case '-':
          if (str[i + 1] != 0 && isdigit(str[i + 1]))
            continue;

          _PREP_AOP_;
          args.push(arg1 - arg2);
          _CHECK_SUB_RES_;
        break;

      case '*':
          _PREP_AOP_;
          _CHECK_MUL_ARG_;
          args.push(arg1 * arg2);
        break;

      case '/':
          _PREP_AOP_;
          _CHECK_DIV_ARG_;
          args.push(arg1 / arg2);
        break;

      default:
        {
          if (isdigit(str[i]) == 0)
            return i + 1;

          char *stop;
          num = strtol(str + i, &stop, rdx);

          if (*stop == 0 || num == LONG_MAX || num == LONG_MIN)
            return i + 1;

          bool bMinus = (i != 0 && str[i - 1] == '-');
          args.push(bMinus ? -num : num);

          i = stop - str;
        }
    }
  }

  if (args.size() == 1)
  {
    res = args.top();
    return 0;
  }

  return -1;
}