parser problem.

I tried to change this parser which was using cin to use stringstream..
when was using cin, everything was going perfectly..
but now if I enter any expression like : 4+5 it'll get stuck on the first char (4 in this exemple..)

But I changed really few things..
added stringstream ist(temp_string);
and then I changed all cin for ist..

Do you guys see anything wrong there?

Code:

---

Token_value get_token()
{
      stringstream ist(temp_string);
      char ch = 0;
      do {                        // skip whitespace except '\n'
        if(!ist.get(ch)) return curr_tok = END;
      }while (ch != '\n' && isspace(ch));
      switch (ch)
      {
          case 0 : case  'E':
                return curr_tok=END;
          case ';' :        return curr_tok = PRINT;
          case '\n' :        line_count.new_line();
          case '*' :
          case '/' :
          case '+' :
          case '-' :
          case '(' :
          case ')' :
          case '=' : return curr_tok = Token_value(ch);
         
          case '0' :        case '1' :        case '2' :        case '3' :        case '4' :
          case '5' :        case '6' :        case '7' :        case '8' :        case '9' :
          case '.' :
                ist.putback(ch);
                ist >> number_value;
                return curr_tok = NUMBER;
          default:                                // NAME, NAME =, or error
                if (isalpha(ch))
                {
                    string_value = ch;
                    while (ist.get(ch) && isalnum(ch)) string_value.push_back(ch);
                    ist.putback(ch);
                    return curr_tok = NAME;
                }
                error("Bad Token");
                return curr_tok = PRINT;
      }
}

---

well Ive used my debugger and my problem seemsto be here:

Code:

---

  do {                        // skip whitespace except '\n'
        if(!ist.get(ch)) return curr_tok = END;
      }while (ch != '\n' && isspace(ch));

---

when I was using cin.get it was going trough the string but now using ist (stringstream) it keeps pointing at the first char?

any suggestion on either why is that so or a way to keep track where it should be pointing at and to go to next char...