RosettaCodeData/Task/Stack/00DESCRIPTION

{{data structure}}[[Category:Classic CS problems and programs]]

A '''stack''' is a container of elements with &nbsp; <big><u>l</u>ast <u>i</u>n, <u>f</u>irst <u>o</u>ut</big>  &nbsp; access policy. &nbsp; Sometimes it also called '''LIFO'''.

The stack is accessed through its '''top'''.

The basic stack operations are:

* &nbsp; ''push'' &nbsp; stores a new element onto the stack top;
* &nbsp; ''pop'' &nbsp; returns the last pushed stack element, while removing it from the stack;
* &nbsp; ''empty'' &nbsp; tests if the stack contains no elements.

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Sometimes the last pushed stack element is made accessible for immutable access (for read) or mutable access (for write):

* &nbsp; ''top'' &nbsp; (sometimes called ''peek'' to keep with the ''p'' theme) returns the topmost element without modifying the stack.

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Stacks allow a very simple hardware implementation.

They are common in almost all processors.

In programming, stacks are also very popular for their way ('''LIFO''') of resource management, usually memory.

Nested scopes of language objects are naturally implemented by a stack (sometimes by multiple stacks).

This is a classical way to implement local variables of a re-entrant or recursive subprogram. Stacks are also used to describe a formal computational framework.

See [[wp:Stack_automaton|stack machine]].

Many algorithms in pattern matching, compiler construction (e.g. [[wp:Recursive_descent|recursive descent parsers]]), and machine learning (e.g. based on [[wp:Tree_traversal|tree traversal]]) have a natural representation in terms of stacks.


;Task:
Create a stack supporting the basic operations: push, pop, empty.


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