LINKED STACKS

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LINKED STACKS

• READ P. 353 - 366

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LINKED STACKS

• Introduction
• again, there is a limitation to lists that was
  discussed earlier (the fixed size of the array
  limits the list)
• in our stack example, we are still limited to
  using only the size specified by the constructor
  for our stack
• a way around that is to combine the concept of a
  linked list and a stack to produce a linked stack
  list
• Implement stack as linked list, and expand or
  shrink the stack through pop and push

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Conceptual Design of Linked Stack

• again, items are only added/removed from one
  place (we'll call it top)
• for the linked stack, only the top node will be
  available, and we'll traverse through the stack
  by following links
• rest of the commands are still the same
• Linked Stack Object
• Knows Top position of stack (position
  pointer)
• Can Do Push an item on stack
• Pop an item from stack
• Tell how many items are
  currently on stack
• Tell if stack is empty /
  Tell if stack is full
• Tell you which item is
  currently sitting on top

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Implementation of the Linked Stack

• typedef int Item
• struct Node
• Item data
• Node link
• class LinkedStack
• public
• LinkedStack()
• Item Top()
• Item Pop()
• void Push(const Item anItem)
• int Size() const
• bool IsEmpty() const
• bool IsFull() const
• private
• Node top //pointer to top of stack

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Linked Stack Member Functions

• The Default Constructor - creates a stack
  dynamically, setting top to point to nothing
• LinkedStack LinkedStack()
• top 0
• The IsEmpty Function - will return true if the
  stack is empty (top points to nothing)
• bool LinkedStack IsEmpty() const
• if (top 0)
• return true
• else
• return false

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Linked Stack Member Functions (cont.)

• The IsFull Function - will return false always
  (dynamic memory being used)
• bool LinkedStack IsFull() const
• return(false)
• The Size Function - moves through the items by
  traversing links , counting as we go
• int LinkedStack Size() const
• Node temp int total 0
• temp top
• while (temp ! 0)
• total
• temp temp-gtlink
• return total

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Linked Stack Member Functions (cont.)

• The Push Function - moves to find the current top
  of stack, and adds the item there
• void LinkedStack Push(const Item anItem)
• Node temp temp new Node
• if (temp 0)
• cout ltlt "out of memory"
• else
• temp-gtdata anItem
• temp-gtlink top
• top temp

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LINKED STACK MEMBER FUNCTIONS (cont.)

• The Pop Function - returns the top item off the
  stack and resets top to point to next item
• Item LinkedStack Pop()
• Item info Node temp
• if (IsEmpty())
• cout ltlt "Cannot pop - stack empty"
  ltlt endl
• return -999
• else
• temp top
• info temp-gtdata
• top temp-gtlink
• delete temp
• return info

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LINKED STACK MEMBER FUNCTIONS (cont.)

• The Top Function - gives back the top item on
  stack but does not remove it
• Item LinkedStack Top() const
• Item info Node temp
• if (IsEmpty())
• cout ltlt "No items on stack "
  ltlt endl
• return -999
• else
• temp top
• info temp-gtdata
• return info

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EXAMPLE REVERSING DIGITS (again)

• void main()
• LinkedStack MyStack
• char InputChar '0'
• cout ltlt "Enter digits to display in
  reverse "
• while (isdigit(InputChar))
• cin gtgt InputChar
• if (isDigit(InputChar))
• MyStack.Push(InputChar)
• char OutputChar
• while (!MyStack.IsEmpty())
• OutputChar MyStack.Pop()
• cout ltlt OutputChar ltlt " "
• cout ltlt endl

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QUESTIONS?

• Read P. 389 - 444 on QUEUES