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In most of the high level languages, a stack can be easily
implemented either through an array or alinked list. What
identifies the data structure as a stack in either case is not the
implementation but theinterface: the user is only allowed to pop or
push items onto the array or linked list, with few otherhelper
operations. Creation of stack means creating array structure
without putting value into it. Thefollowing will demonstrate both
implementations, using C.
The array implementation aims to create an array where the first
element (usually at the zero-offset)is the bottom. That is,
array[0] is placed at the first element pushed onto the stack and
the last elementpopped off. The program must keep track of the
size, or the length of the stack. The stack itself cantherefore be
effectively implemented as a two-element structure in C:
typedef struct {
int size;
int items[STACKSIZE];
} STACK;
The push() operation is used both to initialize the stack, and
to store values to it.
If we use a dynamic array, then we can implement a stack that
can grow or shrink as much as needed.The size of the stack is
simply the size of the dynamic array. A dynamic array is a very
efficientimplementation of a stack.
The linked-list implementation is equally simple and
straightforward. In fact, a simple singly linkedlist is sufficient
to implement a stack-it only requires that the head node or element
can be removed,or popped, and a node can only be inserted by
becoming the new head node.
Unlike the array implementation, our structure typedef
corresponds not to the entire stack structure,but to a single
node:
typedef struct stack {
int data;
struct stack *next;
} STACK;
Such a node is identical to a typical singly linked list node,
at least to those that are implemented in C.
The push() operation both initializes an empty stack, and adds a
new node to a non-empty one. Itworks by receiving a data value to
push onto the stack, along with a target stack, creating a new
nodeby allocating memory for it, and then inserting it into a
linked list as the new head.
Before going into detail we should be familiar with some
operations related to stack. These are givenbelow :-
Creation of Stack
Array
Linked list
Stack Operations
Push: Push means insert any item in stack. The process of adding
a new element to the topof stack is called PUSH operation. Pushing
an element in the stack invoke adding of element, as thenew element
will be inserted at the top after every push operation the top is
incremented by one. Incase the array is full and no new element can
be accommodated, it is called STACK-FULL condition.This condition
is called stack overflow.
Pop : Pop means delete an element from stack. The process of
deleting an element from thetop of stack is called POP operation.
After every pop operation top is decremented by one. If there is no
element on the stack and the pop is performed then this will result
into stack underflow condition.
Top : Top tells about the location from where elements can be
removed or where elementscan be added. It gets the next element to
be removed.
IsEmpty : This is a condition which checks whether the stack is
empty or not, beforeapplying pop operation IsEmpty condition has to
be checked to ensure the presence of an element ina stack.
IsFull : This is a condition which checks whether the stack is
full or not, before applying pushoperation IsFull condition has to
be checked to find out whether there is any space or not to add
anelement in a stack.
Display : This operation is used to display all the elements
present in a stack linearly.
