What is the difference between a stack and a queue?

The main difference between a stack and a queue lies in their fundamental principles of operation and the order in which elements are accessed and removed.

A stack is a data structure that follows the Last-In-First-Out (LIFO) principle. This means that the last element added to the stack is the first one to be removed. It can be visualized as a stack of plates, where you can only access or remove the topmost plate. Elements are added and removed from only one end of the stack, known as the top. This operation is called push (addition) and pop (removal) respectively.

On the other hand, a queue is a data structure that follows the First-In-First-Out (FIFO) principle. This means that the first element added to the queue is the first one to be removed. It can be visualized as a line of people waiting for a bus, where the person who arrived first is the first one to board the bus. Elements are added at one end of the queue, known as the rear or back, and removed from the other end, known as the front. This operation is called enqueue (addition) and dequeue (removal) respectively.

In summary, the key differences between a stack and a queue are:
1. Order of access: Stack follows LIFO, while Queue follows FIFO.
2. Insertion and removal: Stack allows insertion and removal at only one end (top), while Queue allows insertion at the rear and removal from the front.
3. Access to elements: In a stack, only the topmost element is accessible, while in a queue, both the front and rear elements can be accessed.

These differences in principles and operations make stacks and queues suitable for different scenarios and applications.