#include <iostream>

class StackElem
{
// This class will store either a character or double data type.
// The names reflect the intended usage of this class with a program
// for infix to postfix equation translation and postfix equation
// evaluation.

// The class has two data members:
//  the first is an instance of an enumerated type to tell whether
//     the instance of the class is an operator/character or a
//     number/double.  THis value could be undefined in case the
//     instance of the class is created by the default constructor.
//
//  the second is an instance of a union that will hold either the
//     character value or the double value

 public:
   // create the enumerated type to determine the value stored in 
   //  the instance
   enum SEType {UNDEFINED, OPERATOR, NUMBER};

 private:
   // create the union to hold either the character or the double value
   union SEUnion
      {
       char oper;
       double numb;
      };

   // data member definition
   SEType et;		// the instance of the enumerated type
   SEUnion eu;		// the instance of the union

 public:
   // default constructor - type is unknown
   StackElem ()
     {
      et = UNDEFINED;
      eu.oper = '\0';
      eu.numb = 0.0;
     }

   // constructor to set up the instance to hold an operator
   StackElem (char op)
     {
      et = OPERATOR;
      eu.oper = op;
     }

   // constructor to set up the instance to hold a numeric value
   StackElem (double num)
     {
      et = NUMBER;
      eu.numb = num;
     }

   // a method to store an operator in the instance
   void setOperator(char op)
     {
      et = OPERATOR;
      eu.oper = op;
     }

   // a method to store a numeric value in the instance
   void setNumber(double num)
     {
      et = NUMBER;
      eu.numb = num;
     } 

   // a method to return the type of value stored in the instance
   SEType getType()
     {
      return et;
     }

   // a method to access an operator value
   // This method will return true if the instance does indeed
   //   store an operator and false otherwise
   // The method uses a pass-by-reference parameter to send the 
   //   operator value back to the calling code.  If the instance
   //   does not contain an operator the null character is sent 
   //   back to the calling code.
   bool getOperator (char &op)
     {
      if (et == OPERATOR)
         {
          op = eu.oper;
          return true;
         }
      else
         {
          op = '\0';
          return false;
         }
     }

   // a method to access an operator value
   // This method will return the operator value if the
   //   instance does indeed store an operator value.
   //   Otherwise the null character is returned.
   char getOperator ()
     {
      if (et == OPERATOR)
          return eu.oper;
      else
          return '\0';
     }

   // a method to access a numeric value
   // This method will return true if the instance does indeed
   //   store a numeric and false otherwise
   // The method uses a pass-by-reference parameter to send the 
   //   numeric value back to the calling code.  If the instance
   //   does not contain an numeric the value of 0.0 is sent 
   //   back to the calling code.
   bool getNumber (double &num)
     {
      if (et == NUMBER)
         {
          num = eu.numb;
          return true;
         }
      else
         {
          num = 0.0;
          return false;
         }
     }

   // a method to access a numeric value
   // This method will return the numeric value if the
   //   instance does indeed store a numeric value.
   //   Otherwise the value of 0.0 is returned.
   double getNumber ()
     {
      if (et == NUMBER)
          return eu.numb;
      else
          return 0.0;
     }

   // This method is meant for debugging purposes.
   // It outputs the type and value of the instance to cout.
   void output ()
     {
      if (et == UNDEFINED)
         cout << "UNDEFINED.";
      else if (et == OPERATOR)
         cout << "OPERATOR: " << eu.oper;
      else if (et == NUMBER)
         cout << "NUMBER: " << eu.numb;
     }
};


int main()
{
 StackElem se1, se2('+'), se3(3.14159);
 double val;
 char op;

 cout << "Value in se1: ";
 se1.output();
 cout << endl; 
 cout << "Value in se2: ";
 se2.output();
 cout << endl; 
 cout << "Value in se3: ";
 se3.output();
 cout << endl; 
 cout << endl; 

 if (se1.getType() == StackElem::OPERATOR)
    cout << "Value in se1: " << se1.getOperator() << endl;
 if (se1.getType() == StackElem::NUMBER)
    cout << "Value in se1: " << se1.getNumber() << endl;

 if (se2.getType() == StackElem::OPERATOR)
    cout << "Value in se2: " << se2.getOperator() << endl;
 if (se2.getType() == StackElem::NUMBER)
    cout << "Value in se2: " << se2.getNumber() << endl;

 if (se3.getType() == StackElem::OPERATOR)
    cout << "Value in se3: " << se3.getOperator() << endl;
 if (se3.getType() == StackElem::NUMBER)
    cout << "Value in se3: " << se3.getNumber() << endl;  
 cout << endl;

 if (se1.getOperator(op) == true)
    cout << "Value in se1: " << op << endl;
 if (se1.getNumber(val) == true)
    cout << "Value in se1: " << val << endl;

 if (se2.getOperator(op) == true)
    cout << "Value in se2: " << op << endl;
 if (se2.getNumber(val) == true)
    cout << "Value in se2: " << val << endl;

 if (se3.getOperator(op) == true)
    cout << "Value in se3: " << op << endl;
 if (se3.getNumber(val) == true)
    cout << "Value in se3: " << val << endl;
 cout << endl;

 se1.setOperator('*');
 se2.setNumber(-25.2);
 se3.setNumber(123.456);

 cout << "Value in se1: ";
 se1.output();
 cout << endl; 
 cout << "Value in se2: ";
 se2.output();
 cout << endl; 
 cout << "Value in se3: ";
 se3.output();
 cout << endl; 
 cout << endl; 

 if (se1.getOperator(op) == true)
    cout << "Value in se1: " << op << endl;
 if (se1.getNumber(val) == true)
    cout << "Value in se1: " << val << endl;

 if (se2.getOperator(op) == true)
    cout << "Value in se2: " << op << endl;
 if (se2.getNumber(val) == true)
    cout << "Value in se2: " << val << endl;

 if (se3.getOperator(op) == true)
    cout << "Value in se3: " << op << endl;
 if (se3.getNumber(val) == true)
    cout << "Value in se3: " << val << endl;
 cout << endl;

}