1. An Abstract Data Type (ADT), commonly used in most programming languages.*StackQueueData

An Abstract Data Type (ADT) is a high-level description of how data is viewed and manipulated. It defines a data type by its behavior from the point of view of a user, in terms of possible values, possible operations on data of this type, and the behavior of these operations.

Two commonly used ADTs in most programming languages are Stack and Queue.

1. Stack: A stack is a linear data structure that follows a particular order in which the operations are performed. The order may be LIFO(Last In First Out) or FILO(First In Last Out). Mainly the following three basic operations are performed in the stack:

   • Push: Adds an item in the stack. If the stack is full, then it is said to be an Overflow condition.
   • Pop: Removes an item from the stack. The items are popped in the reversed order in which they are pushed. If the stack is empty, then it is said to be an Underflow condition.
   • Peek or Top: Returns the top element of the stack.
   • isEmpty: Returns true if the stack is empty, else false.

2. Queue: A Queue is a linear structure which follows a particular order in which the operations are performed. The order is First In First Out (FIFO). A good example of a queue is any queue of consumers for a resource where the consumer that came first is served first. The difference between stacks and queues is in removing. In a stack we remove the item the most recently added; in a queue, we remove the item the least recently added.