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PUSH and POP algorithms in Linked List implemented STACK in C Language

To implement the STACK using Linked List, the following PUSH and POP algorithms may be used:

Algorithm for PUSH operation in Linked List implemented STACK:

PUSHLL(TOP, ITEM)
[TOP is address of top node of STACK and ITEM is the item to PUSH.[In case of Linked List no overflow, but may be memory allocation error]
If AVAIL=NULL then:
  Write: ’Memory Allocation Error !!!’; Exit.
[End of If]
NEW<--AVAIL
AVAIL<--AVAIL-->LINK
NEW-->INFO<--ITEM
NEW-->LINK<--NULL
If TOP=NULL Then:
  TOP<--NEW
Else:
  NEW-->LINK<--TOP
   TOP<--NEW
[End of If]
Exit.

For Linked List implemented STACK in C, a self-referential structure, a user defined data type STACK is used, it is as follows:
struct STACK
  {
    int i:
    STACK *link:
   };

Algorithm for POP operation in Linked List implemented STACK.
POPLL(TOP)
[TOP is the address of TOP node of STACK]
If TOP=NULL Then:
   Write: ‘Underflow’
   Exit.
[End of If]
ITEM <--TOP-->INFO
TOP<--TOP-->LINK
Return ITEM
Exit.

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Memory representation of Linked List Data Structures in C Language

Memory representation of Linked List

             In memory the linked list is stored in scattered cells (locations).The memory for each node is allocated dynamically means as and when required. So the Linked List can increase as per the user wish and the size is not fixed, it can vary.

               Suppose first node of linked list is allocated with an address 1008. Its graphical representation looks like the figure shown below:


      Suppose next node is allocated at an address 506, so the list becomes,



  Suppose next node is allocated with an address with an address 10,s the list become,


The other way to represent the linked list is as shown below:




 In the above representation the data stored in the linked list is “INDIA”, the information part of each node contains one character. The external pointer root points to first node’s address 1005. The link part of the node containing information I contains 1007, the address of next node. The last node …