Qu'est-ce (qui) est push down - définition
![datum]] on the stack. A push operation decrements the pointer and copies the data to the stack; a pop operation copies data from the stack and then increments the pointer. Each procedure called in the program stores procedure return information (in yellow) and local data (in other colors) by pushing them onto the stack. This type of stack implementation is extremely common, but it is vulnerable to [[buffer overflow]] attacks (see the text).](https://commons.wikimedia.org/wiki/Special:FilePath/ProgramCallStack2 en.svg?width=200 "datum]] on the stack. A push operation decrements the pointer and copies the data to the stack; a pop operation copies data from the stack and then increments the pointer. Each procedure called in the program stores procedure return information (in yellow) and local data (in other colors) by pushing them onto the stack. This type of stack implementation is extremely common, but it is vulnerable to [[buffer overflow]] attacks (see the text).")
![[[Dornier Seawings Seastar]]](https://commons.wikimedia.org/wiki/Special:FilePath/Dornier Seastar D-ICKS.jpg?width=200 "[[Dornier Seawings Seastar]]")
![Rutan Model 40 Defiant]]](https://commons.wikimedia.org/wiki/Special:FilePath/Rutan-Defiant-N57KS.jpg?width=200 "Rutan Model 40 Defiant]]")
![Rutan Model 76 Voyager]]](https://commons.wikimedia.org/wiki/Special:FilePath/VoyagerAircraftAtNASM-common.jpg?width=200 "Rutan Model 76 Voyager]]")
![[[Adam A500]]](https://commons.wikimedia.org/wiki/Special:FilePath/Adam500-N504AX-051111-02.jpg?width=200 "[[Adam A500]]")
![[[Network Rail]] [[Driving Brake Standard Open]] in October 2009](https://commons.wikimedia.org/wiki/Special:FilePath/DBSO 9714 Ogston.jpg?width=200 "[[Network Rail]] [[Driving Brake Standard Open]] in October 2009")
![Alnmouth]] in June 2005](https://commons.wikimedia.org/wiki/Special:FilePath/GNER train steams into Alnmouth Station - 07 June 2005.jpg?width=200 "Alnmouth]] in June 2005")
![A single [[GWR Autocoach]] capable of steam push–pull operation](https://commons.wikimedia.org/wiki/Special:FilePath/GWR Autocoach.jpg?width=200 "A single [[GWR Autocoach]] capable of steam push–pull operation")
![A [[Metra]] train in push mode, with a non-locomotive passenger car in the front. Note the engineer's station in the upper level of the passenger car.](https://commons.wikimedia.org/wiki/Special:FilePath/Geneva Metra 071020.jpg?width=200 "A [[Metra]] train in push mode, with a non-locomotive passenger car in the front. Note the engineer's station in the upper level of the passenger car.")
![Push–pull train in [[Slovakia]]](https://commons.wikimedia.org/wiki/Special:FilePath/Lokomotiva 109 E2.jpg?width=200 "Push–pull train in [[Slovakia]]")
![driving van trailer]] in [[Ireland]]](https://commons.wikimedia.org/wiki/Special:FilePath/Mallow IÉ-4006.jpg?width=200 "driving van trailer]] in [[Ireland]]")
![A [[New Jersey Transit]] train with [[Bombardier ALP-46]] locomotives on both ends and 11 cars in between, in [[New Jersey]], United States.](https://commons.wikimedia.org/wiki/Special:FilePath/NEC train 3967 passing through Rahway station, June 2007.jpg?width=200 "A [[New Jersey Transit]] train with [[Bombardier ALP-46]] locomotives on both ends and 11 cars in between, in [[New Jersey]], United States.")
Wikipédia
In computer science, a stack is an abstract data type that serves as a collection of elements, with two main operations:
- Push, which adds an element to the collection, and
- Pop, which removes the most recently added element that was not yet removed.
Additionally, a peek operation can, without modifying the stack, return the value of the last element added. Calling this structure a stack is by analogy to a set of physical items stacked one atop another, such as a stack of plates.
The order in which an element added to or removed from a stack is described as last in, first out, referred to by the acronym LIFO. As with a stack of physical objects, this structure makes it easy to take an item off the top of the stack, but accessing a datum deeper in the stack may require taking off multiple other items first.
Considered as a linear data structure, or more abstractly a sequential collection, the push and pop operations occur only at one end of the structure, referred to as the top of the stack. This data structure makes it possible to implement a stack as a singly linked list and as a pointer to the top element. A stack may be implemented to have a bounded capacity. If the stack is full and does not contain enough space to accept another element, the stack is in a state of stack overflow.
A stack is needed to implement depth-first search.
