The C++ Stack is a container adapter that gives the programmer the functionality of a stack – specifically, a FILO (first-in, last-out) data structure.
| Constructors | construct a new stack | 
| empty | true if the stack has no elements | 
| pop | removes the top element of a stack | 
| push | adds an element to the top of the stack | 
| size | returns the number of items in the stack | 
| top | returns a reference to the top element of the stack |