STACK is explained as follows:

A stack is one of the most usually used data structure. A stack is also called a Last-In-First-Out (LIFO) system, is a linear list in which insertion or deletion can take place only at one end called the top. This structure operates in the identical way as the stack of trays if we want to place another tray, it can be placed only at the top. Likewise, if we want to remove a tray from stack of trays, it can only be removed from the top. The insertion and removal operations in stack terminology are known as PUSH and POP operation.

(a)  Stack after the pushing of elements 8,10,12,5,6

(b) Stack after the popping of 2 elements.

Implementation of Stack is explained below

Stacks can be implemented in the below given two ways ways:

a)  Arrays is also implementation of stacks

b)  Linked List is also implementation of stacks

a)  Arrays:- To implement a stack we require a variable called top, that holds the index of the top element of stack and an array to hold the element of the stack.

For example:-     #define MAX 100

Typedef struct

{ int top;

int elements [MAX]

} stack;

b)  Linked List:- A stack represented by making use of a linked list is known as linked stack. The array based representation of stack suffers from the certain limitations.

        Size of stack must be known to us in advance

        Overflow condition may occur.

The linked representation allows a stack to develop to a limit of the computer's memory.

for example:-      typedef struct node

{

int info;

struct node * next;

} stack;

stack * top;