Is there an object of type integer that isn't a number?

[JKLolling]

Hi All,
I have a function that returns the top value in a stack, but only if the stack is not empty. My question is, what value should I return if the stack is empty? The function needs to return an integer, but any integer I return could conceivably be a value in the stack. Is there something I can return that is of type integer, yet isn't an actual number? Here is my code:

  int top()
  {
       if(!isEmpty())
           return stack[current_size];
       else
           return ?;
  }

[Peter87]

You could throw an exception.

http://www.cplusplus.com/doc/tutorial/exceptions/

[gunnerfunner]

top() needs to return int but what about isEmpty(), can't you have it return bool? In that case:

 int top()
  {
       if(!isEmpty())
           return stack[current_size];
       else
           return (isEmpty() - 1);//edit: should be isEmpty() - 1;
  }

[cire]

top() needs to return int but what about isEmpty(), can't you have it return bool? In that case:

top would still be returning a valid value. I would second Peter87's suggestion, but failing that, document that using top when isEmpty returns a value of true results in undefined behavior.

[JKLolling]

Thanks for your help guys!