The document explains the Stack ADT (Abstract Data Type), which is a linear data structure following the Last In, First Out (LIFO) principle. It details operations such as push, pop, and top, along with errors like overflow and underflow, while providing examples and implementations using arrays and linked lists. The summary highlights the key concepts and functionality of stacks in data structures and algorithms.

1. Mr. P. Seethamani
Assistant Professor /IT
Topic : Stack ADT
19CSSC2401-Data Structures and Algorithms
IT2311-Data Structures and
Algorithms

2. Contents
• Stack Introduction
• Stack model
• Operations of Stack
19CSSC2401-Data Structures and Algorithms

3. Stack
• A stack is an ordered collection of elements in which all elements are
insert and delete at one end called top.
• It is a linear data structure.
• A Stack is a data structure following the LIFO(Last In, First Out)
principle.
• Its also called as Push down list
• Examples:
• Stack of coins / books
• Undo/Redo operations
• Page visited history in a Web browser
19CSSC2401-Data Structures and Algorithms

4. Stack Model (input to a stack is by push, output is by
pop)
19CSSC2401-Data Structures and Algorithms
Push(X)
Pop (X)
Top (S)
Element3
Element2
Element1
Element4
Stack Model

5. Stack
Top of Stack
Book 5
Book 4
Book 3
Book 2
Book 1
Stack of Books
19CSSC2401-Data Structures and Algorithms

6. Examples for Stack
19CSSC2401-Data Structures and Algorithms

7. 19CSSC2401-Data Structures and Algorithms
Stack ADT
• Stack ADT is a sequence of elements following LIFO
principle.
• Basic Operations
1. Push
2. Pop
3. Top

8. Operations of Stack
push(data) adds an element to the top of the stack
pop() removes an element from the top of the stack
peek()
returns a copy of the element on the top of the stack without
removing it
is_empty() checks whether a stack is empty
is_full()
checks whether a stack is at maximum capacity when stored in a
static (fixed-size) structure
19CSSC2401-Data Structures and Algorithms

9. 19CSSC2401-Data Structures and Algorithms
Operations of Stack
• Initially Stack is Empty.
• Size of stack is 6

10. Standard errors in stack
• There are two errors occurred at the time of operations
performed on the stack.
• Overflow:
• Attempt to insert an element when stack is full, is said to be
overflow of stack.
• Underflow:
• attempt to delete/remove an element when stack is empty, is
said to be underflow
19CSSC2401-Data Structures and Algorithms

11. Stack - LIFO
• Last In First Out (LIFO) – last item to be inserted into the Stack
will be the first to be deleted
• Apply insertion operations(insert 1, 2, 3)
19CSSC2401-Data Structures and Algorithms
Empty
Stack
1
Push(1)
2
1
Push(2)
3
2
1
Push(3)
3
2
1
Push(4)
Overflow Error will displayed
if Stack is Full

12. Stack - LIFO
• Apply delete operations
• Order of deletion is the reverse of the order of insertion
• Insertion order – 1, 2, 3
• Deletion order - 3, 2, 1
19CSSC2401-Data Structures and Algorithms
3
2
1
Full Stack
2
1
Delete
1
Delete Delete –
Empty
Stack
Stack
Empty
condition

13. Stack – Push operation
• The process of inserting a new data element onto stack is known as a Push
Operation. Push operation involves a series of steps −
Step 1 − Checks if the stack is full.
Step 2 − If the stack is full, produces an error and exit.
Step 3 − If the stack is not full, increments top to point next empty space.
Step 4 − Insert data element to the stack location, where top is pointing.
Step 5 − Returns success.
19CSSC2401-Data Structures and Algorithms

14. 19CSSC2401-Data Structures and Algorithms
Stack – Push operation

15. Stack – Pop operation
• Accessing the content while removing it from the stack, is known as a Pop
Operation. In pop() operation, top is decremented to a lower position in the
stack to point to the next value.
• A Pop operation may involve the following steps −
Step 1 − Checks if the stack is empty.
Step 2 − If the stack is empty, produces an error and exit.
Step 3 − If the stack is not empty, accesses the data element at which top is
pointing.
Step 4 − Decreases the value of top by 1.
Step 5 − Returns success.
19CSSC2401-Data Structures and Algorithms

16. 19CSSC2401-Data Structures and Algorithms
Stack – Pop operation

17. Stack – Top operation
• Examines or views the element on the top of Stack
• Size of Stack does not change
• Check for Stack Empty or Underflow condition before Top
• Top pointer is not altered
19CSSC2401-Data Structures and Algorithms

18. Stack - Implementation
• Implementation
• Arrays Implementation (static: the size of stack is given
initially)
• Linked lists Implementation (dynamic: never becomes
full)
19CSSC2401-Data Structures and Algorithms

19. Summary
Stack data structure
• Nature - Last In First Out (LIFO)
• Operations - Push, Pop and Top
19CSSC2401-Data Structures and Algorithms