A stack is a collection of items or elements used in programming languages. It is usually referred to as an abstract data type (ADT) as it provides abstract or essential details of its implementation (using an array or linked list). A stack is based on linear data structure or works on the principle of Last In First Out (LIFO) or First in Last out (FILO). It consists of two main operations named Push (adding data to the stack) and Pop (removing data from the stack). A stack has only one end; therefore, its operations happen on the top position.
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Further, a stack may have either a fixed size or a dynamic implementation. However, if an attempt is made to push an element while the stack is already full, it causes a stack overflow. On the other hand, whenever an attempt is made to remove an element from an empty stack, then it leads to stack underflow.
When a new element is added to the stack, the stack pointer or register moves to the new element and copies that element to the register. Typically, a stack consists of a linear sequence of items in contrast to a queue that follows the principle of First in First out (FIFO).
The term is often used in discussing allocation and access of system memory in computers. Key stack operations include:
The implementation is a stack is done using the linked lists or using arrays.
There is no pre-allocated storage for the stack with linked list implementation. It allocates memory as nodes according to the run time requirements. In a linked list, only one private data member, or stack pointer, is required by the class, and it’s the node at the top of the stack.
Stack implementation using an array is easy as it includes a dimensional array of a specific size. Due to the specific size of the array, it becomes easy to either delete or add values into the array by leveraging the principle of LIFO. The pointer concept is not involved in array implementation as memory is fixed.
Here are some of the top applications of a stack:
Finally, stacks can be used to reverse the order of elements or items. Stacks efficiently allocate space; therefore, memory never gets fragmented. However, it possesses predefined storage space, and it’s not flexible.