/*****************************************************
  Author  : Yan Huang
  Date    : 02.27.07
  Synopsis: convert a infix expression to a postfix expression
            Note: Some codes have been purposely taken out. 
                  and the precedence is not set properly.
**************************************************************/

#include <stack>
#include <iostream>
using namespace std;


/************************************************
    Get the next token, symbol is the character
    representation, which is returned, the token is
    represented by its enumerated value, which
    is returned in the function name
***************************************************/

enum tokenEnum{lparen,rparen,plus,minus,divide,times,mod,eos,operand};
int  precedence[]= {1,2,3,4,5,1,1,3,4,1,1};
char tokenSymbol[]= {'(',')','+','-','/','*','%','\n'};


tokenEnum get_token()
{
  char symbol;

  symbol = cin.get();

  /* get rid of the space */
  while (symbol == ' '){
      symbol = cin.get();
  }

  switch (symbol)  {
     case '(' : return lparen;
     case ')' : return rparen;
     case '+': return plus;
     case '-' : return minus;
     case '/' :  return divide;
     case '*' : return times;
     case '%' : return mod;
     case 'E' : return eos;
     default  : cin.unget(); return operand;
     /* no error checking, default is operand */
     }
}

void main()
{
/* output the postfix of the expression. The expression
    string, the stack, and top are global */

   char symbol;
   tokenEnum token;
   int op;
   stack <char> myStack; 

   for (token = get_token(); token != eos; token = get_token()) {
     if (token is operand){
        cin >> op;
        cout << op;
     }  else if (token == lparen) {
          myStack.push(token);
    } else if (token == rparen ){
      /*unstack tokens until left parenthesis */
        ...
      }
      myStack.pop();
    } else{
      /* remove and print symbols whose precedence is greater
          than or equal to the current token's precedence and the stack is not empty and 
          before we see left parenthesis*/
      while(!myStack.empty() && precedence[myStack.top()] >= precedence[token] &&
          myStack.top() !=lparen){
            ...
      }
      myStack.push(token);
    }
  }
  while (!myStack.empty()){
       cout << tokenSymbol[myStack.top()];
       myStack.pop();
  }
  cout << endl;
}