//stackexp.h
#ifndef _SEXP
#define _SEXP
#include<iostream.h>
 class stackexp
{
 public:
   virtual void print(void)=0;
};
 class stackemp:public stackexp
{
 public:
   void print(void);
};
class stackful:public stackexp
{
 public:
   void print(void);
};
void stackemp::print(void)
{
 cout<<"棧已空!"<<endl;
}
void stackful::print(void)
{
 cout<<"棧已滿!"<<endl;
}
#endif