1. Stacks and Queues
Chapter 4

2. 4.1 Stacks
A stack is a linear data structure that can be accessed only at one of its ends for storing and retrieving.
Its called LIFO.
A stack is defined in terms of operations that change its status and operations that check this status.:
Clear()
isEmpty()
Push(el)
Pop()
topEl()

3. Stack is useful when data have to be stored and then retrieved in reverse order.
An application example of the stack is in matching delimiters in a program.
parentheses, square brackets, curly brackets, and comment delimiters.
Ex: a= b + (c-d) * (e-f)
The program could have nested delimitiers.

4. The delimiters matching algorithm in C++

8. A stack is a last in, first out (LIFO) abstract data type and data structure . A stack can have any abstract data type as an element ,but is characterized by only two fundamental operations: push and pop.
Elements are removed from the stack in the reverse order to the order of their addition :therefore, the lower elements are those that have been on the stack the longest.

10. Basic Operations on a Stack
InitializeStack:
Initializes the stack to an empty state.
DestroyStack:
Removes all the elements from the stack, leaving the stack empty.
IsEmptyStack:
Checks whether the stack is empty. If empty, it returns true; otherwise, it returns false.
IsFullStack:
Checks whether the stack is full. If full, it returns true; otherwise, it returns false

11. Basic Operations on a Stack
Push:
Add new element to the top of the stack
The input consists of the stack and the new element.
Prior to this operation, the stack must exist and must not be full
Top:
Returns the top element of the stack.
Prior to this operation, the stack must exist and must not be empty.
Pop:
Removes the top element of the stack.

12. Operations: initialize destroy build from given data (set of elements)
check if it is empty
get the total size of the stack
add an element to the top of the stack [PUSH]
delete an element from the top of the stack [POP]
get the data from the element at the top of the stack
update the data of the top element
print the data of the top element
print the entire stack

13. In stack , no search, no adding in arbitrary positions, no sorting,
no access to anything beyond the top element.

14. Check for enough room, (no overflow)
Data
Push
Top
Top
operation

15. Check if empty, (no underflow)
Data
Top
Pop
Top
operation

16. Check if empty, (no underflow)
Data
Top
Top
Stack top
operation

17. Top
(a) Conceptual
count
Head
Data nodes
(a) Physical

18. Stack Linked List Implementation
count <integer>
top <node pointer>
end stack
node
data <datatype>
next <node pointer>
end node
count
top
Stack head structure
data
next
Stack node structure

19. Stack Algorithms Create stack algorithm createStack?
count
(a) Before Create
top
stack
algorithm createStack
Initializes metadata for a stack.
stack.head = null
stack.count = 0
Return
end createStack
count
(b) After Create
top
stack

20. Push stack If (stack full) else end if Return successes end pushStack
algorithm pushStack
Insert (push) data into a new node in the liked list.
Post data have been pushed in stack
Return true if successful, false if memory overflow
If (stack full)
successes = false
else
allocate (newptr)
newptr->data = data
newptr->next = stack.top
stack.top = newptr
stack.count = stack.count + 1
successes = true
end if
Return successes
end pushStack
Push stack

21. Pop stack If (stack empty) else end if return successes end popStack
algorithm popStack
This algorithm pops the item on the top of the stack and returns it to the user
Post data have been returned to calling algorithm
Return true if successful, false if underflow
If (stack empty)
successes = false
else
dptr = stack.top
dataout = stack.top->data
stack.top = stack.top->next
stack.count = stack.count – 1
Recycle (dptr)
successes = true
end if
return successes
end popStack
Pop stack

22. Stack Top If (stack empty) else end if return successes end Stacktop
algorithm Stacktop
This algorithm receives the data from the top of the stack without changing the stack.
Post data have been returned to calling algorithm
Return true if data returned, false if underflow
If (stack empty)
successes = false
else
dataout = stack.top->data
successes = true
end if
return successes
end Stacktop

23. Empty Stack If (stack not empty) else end if return result
algorithm emptyStack
Determines if stack is empty and returns a Boolean.
Post returns stack status
Return Boolean, true: stack empty, false: stack contains data
If (stack not empty)
result = false
else
result = true
end if
return result
end emptyStack

24. Full Stack If (memory available) else end if return result
algorithm fullStack
Determines if stack is full and returns a Boolean.
Post returns stack status
Return Boolean, true: stack full, false: stack is empty
If (memory available)
result = false
else
result = true
end if
return result
end fullStack

25. Stack Count return (stack.count) end Stackcount algorithm Stackcount
Returns the number of elements currently in stack.
Post returns stack count
Return integer count of number of elements in stack
return (stack.count)
end Stackcount

26. Destroy Stack Loop (stack.top not null) end loop Stack.count = 0
algorithm destroyStack
This algorithm releases all nodes back to dynamic memory
Loop (stack.top not null)
temp = stack.top
Stack.top = stack.top->next
recycle (temp)
end loop
Stack.count = 0
return
end destroyStack