Data Structures - Stack Implementation as a Class

        # include< iostream.h>
  # include< process.h>
  # include< conio.h>
  # define SIZE 20
  class stack
  {
    int a[SIZE];
    int tos; // Top of Stack
    public:
       stack();
       void push(int);
       int pop();
       int isempty();
       int isfull();
  };
  stack::stack()
  {
    tos=0; //Initialize Top of Stack
  }
  int stack::isempty()
  {
    return (tos==0?1:0);
  }
  int stack::isfull()
  {
    return (tos==SIZE?1:0);
  }
  void stack::push(int i)
  {
    if(!isfull())
    {
      a[tos]=i;
      tos++;
    }
    else
    {
       cerr<<"Stack overflow error !
      Possible Data Loss !";
    }
  }
  int stack::pop()
  {
    if(!isempty())
    {
      return(a[--tos]);
    }
    else
    {
      cerr<<"Stack is empty! What to pop...!";
    }
    return 0;
  }
  void main()
  {
    stack s;
    int ch=1,num;
    while(ch!=0)
    {
       cout<<"Stack Operations Mani Menu
      1.Push
      2.Pop
      3.IsEmpty
      4.IsFull
      0.Exit
      ";
       cin>>ch;
       switch(ch)
       {
         case 0:
           exit(1); //Normal Termination of Program
         case 1:
           cout<<"Enter the number to push";
           cin>>num;
           s.push(num);
           break;
         case 2:
           cout<<"Number popped from the stack is: "<< s.pop()<< endl;
           break;
         case 3:
           (s.isempty())?(cout<<"Stack is empty."):(cout<<"Stack is not empty.");
           break;
         case 4:
           (s.isfull())?(cout<<"Stack is full."):(cout<<"Stack is not full.");
           break;
         default:
           cout<<"Illegal Option.Please try again";
       }
    }//end of while
    getch();
  }