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Implementation of STACK using Linked List in C language

Implementation of STACK using Linked List

             To implement the STACK using Linked List, the Linked List itself is created in different manner. In this case instead of ROOT in normal Linked List, an external pointer TOP is used to point all the time to the just added node.
      Initially when the STACK is empty TOP points to a NULL address.

When the PUSH operation is to be done, a NEW node is created and TOP is made point to it. Suppose for the first time one PUSH operation is done. The linked list is shown below:

When again another ITEM is PUSHed, a NEW node is created and the address of the node pointer by TOP, is copied in the LINK field of NEW node the TOP is made point to the NEW node. The Linked List is as below:
When again another item is to be PUSHed it is done similarly. After the PUSH of one more ITEM the Linked List is as shown below:
So, the Linked List created as STACK can be graphically shown as below:
While deletion, POPping is to be done from the STACK, TOP is checked. If it is NULL then the STACK is empty and ‘underflow’ occurs otherwise the ITEM of the node pointed by TOP can be copied in a variable and TOP is updated by link of TOP. Then ITEM is returned.
                      In the above-created STACK, if the POP operation is done once, the Linked List can be shown as below:


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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 …