What are the characteristics of stack ADTs?

Stack ADTs, or Abstract Data Types, are characterised by their LIFO (Last In, First Out) order of operation, limited access, and dynamic size.

A stack ADT is a linear data structure that follows a particular order in which operations are performed. The order is LIFO, which stands for Last In, First Out. This means that the last element added to the stack will be the first one to be removed. This characteristic is fundamental to the nature of stack ADTs and differentiates them from other data structures such as queues, which operate on a FIFO (First In, First Out) basis.

Another key characteristic of stack ADTs is their limited access. Unlike arrays or linked lists where you can access any element at any time, in a stack, you can only access the top element. This is due to the LIFO principle. You can't access or find an element in the middle of the stack without removing all the elements above it first. This limited access is actually beneficial in certain applications where we want to restrict data access for simplicity or security.

Stack ADTs also have a dynamic size. This means that the size of the stack can change during the execution of the program. Elements can be added or removed from the stack, and it will grow or shrink accordingly. This dynamic size makes stacks a very flexible data structure, as they can adapt to the needs of the program at runtime.

In terms of operations, stack ADTs typically support several key operations. These include 'push' (adding an element to the top of the stack), 'pop' (removing the top element from the stack), 'peek' or 'top' (viewing the top element without removing it), and 'isEmpty' (checking if the stack is empty). These operations allow for the manipulation and examination of the stack.

In summary, stack ADTs are a type of data structure characterised by their LIFO order of operation, limited access to elements, dynamic size, and support for key stack operations. They are a fundamental tool in computer science, used in a variety of applications from parsing expressions to managing function calls in a program.