Stacks

1
Stacks

• CS-240
• Dick Steflik

2
Stacks

• Last In, First Out operation - LIFO
• As items are added they are chronologically
  ordered, items are removed in reverse
  chronological order (newest first)

3
Applications

• reversing the items in a list
• returning from a function/subroutine
• evaluation of postfix expressions
• converting infix expressions to postfix
• localization of parameters and variables in a
  function

4
Overflow and Underflow

• Stack overflow is the condition that arises when
  you attempt adding (pushing) an item onto an
  already full stack.
• To avoid always check isFull( ) before adding
• Stack Underflow is the condition that arises when
  you attempt to remove (pop) an item from an
  already empty stack
• To avoid always check isEmpty before popping

5
Normal methods

• constructor - create and initialize a stack
  object
• copy constructor - create a stack object that is
  a duplicate of another existing stack object
  (this method needed to insure correct value
  semantics)
• overloaded assignment operator - assign the value
  of an existing stack object (a) to another
  existing stack object (b) so that the result is
  that b is a duplicate of a (this method needed to
  insure correct value semantics)
• destructor - destroy a stack object by returning
  any of its dynamic storage back to the heap and
  setting its static elements to NULL or zero

6
Methods

• push - add an item (as the most recent)
• pop - delete the most recently added item
• pull - return the value of the most recently
  added item then delete the item
• peek - return the value of the most recently
  added item
• ifFull - return false/true depending if the stack
  is full true if it is, false otherwise
• isEmpty - return false/true depending if the
  stack is empty true if it is, false otherwise

7
Private data strategies

• use an array to hold items and use an int as an
  index for the array to indicate where the next
  item is to go
• same as above, but use a dynamic array
• use a struct to define a node and add nodes
  dynamically as they are needed use one static
  pointer to a node at point at most recently added
  item(top of stack)

8
Static Static Implementation
Class Stack public Stack( )
top 0 ) void push(int v)
datatop v void pop( )
--top int pull( ) return
datatop-- int peek( ) return
datatop ) boolean isFull( )
return top 20 boolean isEmpty(
) return top 0 private
int data20 int top
9
Dynamic Array Implementation
Class Stack public Stack( )
size 20 top 0 data new int20
Stack( int s ) size s top 0
data new ints ) void push(int
v) if (this.isFull( )) temp new
intsize2 size size 2

for (int j 0 j lt top j)

tempj dataj

delete data data temp
datatop v
int pop( ) return data--top
boolean isFull( ) return top size
boolean isEmpty( ) return top 0
private int data
int top int size
10
Dynamic (nodal) implementation
Class Stack public Stack( )
top NULL ) Stack( ) while
(!this.isEmpty()) this.pop( )
void push(int v) node temp new node()
temp -gt data v
temp -gtnext top top temp
int pull( ) int value top-gtdata
node temp top-gtnext delete top top
temp void pop( ) node temp
top-gtnext delete top top temp
boolean isEmpty( ) return top NULL
private struct node int data
node next
node top