/*
 * *****************************************************************************
 * file name  : Postfix_Evaluator.h
 * author     : Hung Ngo
 * description: interface to the Postfix_Evaluator class
 * *****************************************************************************
 */


#ifndef _POSTFIX_EVALUATOR_H
#define _POSTFIX_EVALUATOR_H

#include <stack>
#include "Lexer.h"

class Postfix_Evaluator {
    public:
    // constructors
    Postfix_Evaluator(Lexer lxer=Lexer("")) : lexer(lxer), operand_stack() {}

    // evaluate the expression
    void set_expression(Lexer);
    double eval();

    private:
    // given an operator op, and two operands a and b, return (a op b)
    double eval_op(char, double, double);
    Lexer lexer;
    std::stack<double> operand_stack;
};

#endif