C Plus Data Structures

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C Plus Data Structures

• Nell Dale
• David Teague
• Chapter 5
• Stack Structures
• Slides by Sylvia Sorkin, Community College of
  Baltimore County - Essex Campus

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Definition of Stack

• Logical (or ADT) level A stack is an ordered
  group of homogeneous items (elements), in which
  the removal and addition of stack items can take
  place only at the top of the stack.
• A stack is a LIFO last in, first out structure.

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Stack ADT Operations

• MakeEmpty -- Sets stack to an empty state.
  
• IsEmpty -- Determines whether the stack is
  currently empty.
• IsFull -- Determines whether the stack is
  currently full.
• Push (ItemType newItem) -- Adds newItem to the
  top of the stack.
• Pop (ItemType item) -- Removes the item at the
  top of the stack and returns it in item.

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ADT Stack Operations

• Transformers
• MakeEmpty
• Push
• Pop
• Observers
• IsEmpty
• IsFull

change state observe state
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Another Stack Implementation

• One advantage of an ADT is that the kind of
  implementation used can be changed.
• The dynamic array implementation of the stack has
  a weakness -- the maximum size of the stack is
  passed to the constructor as parameter.
• Instead we can dynamically allocate the space for
  each stack element as it is pushed onto the
  stack.

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class StackTypeltchargt
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class StackTypeltfloatgt
23.4 -7.9
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class StackTypeltStrTypegt
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Tracing Client Code
V
letter
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Tracing Client Code
letter
V
Private data topPtr NULL
char letter V StackTypelt char gt
myStack myStack.Push(letter) myStack.Push(C)
myStack.Push(S) if ( !myStack.IsEmpty( )
) myStack.Pop( letter ) myStack.Push(K)

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Tracing Client Code
letter
V
Private data topPtr
V
char letter V StackTypelt char gt
myStack myStack.Push(letter) myStack.Push(C)
myStack.Push(S) if ( !myStack.IsEmpty( )
) myStack.Pop( letter ) myStack.Push(K)

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Tracing Client Code
letter
V
Private data topPtr
C V
char letter V StackTypelt char gt
myStack myStack.Push(letter) myStack.Push(C)
myStack.Push(S) if ( !myStack.IsEmpty( )
) myStack.Pop( letter ) myStack.Push(K)

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Tracing Client Code
letter
V
Private data topPtr
S C V
char letter V StackTypelt char gt
myStack myStack.Push(letter) myStack.Push(C)
myStack.Push(S) if ( !myStack.IsEmpty( )
) myStack.Pop( letter ) myStack.Push(K)

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Tracing Client Code
letter
V
Private data topPtr
S C V
char letter V StackTypelt char gt
myStack myStack.Push(letter) myStack.Push(C)
myStack.Push(S) if ( !myStack.IsEmpty( )
) myStack.Pop( letter ) myStack.Push(K)

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Tracing Client Code
letter
S
Private data topPtr
C V
char letter V StackTypelt char gt
myStack myStack.Push(letter) myStack.Push(C)
myStack.Push(S) if ( !myStack.IsEmpty( )
) myStack.Pop( letter ) myStack.Push(K)

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Tracing Client Code
letter
S
Private data topPtr
K C V
char letter V StackTypelt char gt
myStack myStack.Push(letter) myStack.Push(C)
myStack.Push(S) if ( !myStack.IsEmpty( )
) myStack.Pop( letter ) myStack.Push(K)

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Dynamically Linked Implementation of Stack

• // DYNAMICALLY LINKED IMPLEMENTATION OF STACK
• include "ItemType.h" // for ItemType
• templateltclass ItemTypegt
• struct NodeType
• ItemType info
• NodeTypeltItemTypegt next

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• // DYNAMICALLY LINKED IMPLEMENTATION OF STACK
  continued
• templateltclass ItemTypegt
• class StackType
• public
• StackType( ) // constructor
• // Default constructor.
• // POST Stack is created and empty.
• void MakeEmpty( )
• // PRE None.
• // POST Stack is empty.
• bool IsEmpty( ) const
• // PRE Stack has been initialized.
• // POST Function value (stack is empty)
• bool IsFull( ) const
• // PRE Stack has been initialized.
• // POST Function value (stack is full)

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• // DYNAMICALLY LINKED IMPLEMENTATION OF STACK
  continued
• void Push( ItemType item )
• // PRE Stack has been initialized.
• // Stack is not full.
• // POST newItem is at the top of the stack.
• void Pop( ItemType item )
• // PRE Stack has been initialized.
• // Stack is not empty.
• // POST Top element has been removed from
  stack.
• // item is a copy of removed element.
• StackType( ) // destructor
• // PRE Stack has been initialized.
• // POST Memory allocated for nodes has been
• // deallocated.
• private
• NodeTypeltItemTypegt topPtr

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• // DYNAMICALLY LINKED IMPLEMENTATION OF STACK
  continued
• // member function definitions for class
  StackType
• templateltclass ItemTypegt
• StackTypeltItemTypegtStackType( ) //
  constructor
• topPtr NULL
• templateltclass ItemTypegt
• void StackTypeltItemTypegtIsEmpty( ) const
• // Returns true if there are no elements
• // on the stack false otherwise
• return ( topPtr NULL )

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Using operator new

• If memory is available in an area called the free
  store (or heap), operator new allocates the
  requested object, and returns a pointer to the
  memory allocated.
• The dynamically allocated object exists until the
  delete operator destroys it.

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Adding newItem to the stack
newItem
B

• newItem B
• NodeTypeltchargt location
• location new NodeTypeltchargt
• location-gtinfo newItem
• location-gtnext topPtr
• topPtr location

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Adding newItem to the stack
newItem
B

• newItem B
• NodeTypeltchargt location
• location new NodeTypeltchargt
• location-gtinfo newItem
• location-gtnext topPtr
• topPtr location

location
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Adding newItem to the stack
newItem
B

• newItem B
• NodeTypeltchargt location
• location new NodeTypeltchargt
• location-gtinfo newItem
• location-gtnext topPtr
• topPtr location

location
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Adding newItem to the stack
newItem
B

• newItem B
• NodeTypeltchargt location
• location new NodeTypeltchargt
• location-gtinfo newItem
• location-gtnext topPtr
• topPtr location

B
location
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Adding newItem to the stack
newItem
B

• newItem B
• NodeTypeltchargt location
• location new NodeTypeltchargt
• location-gtinfo newItem
• location-gtnext topPtr
• topPtr location

B
location
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Adding newItem to the stack
newItem
B

• newItem B
• NodeTypeltchargt location
• location new NodeTypeltchargt
• location-gtinfo newItem
• location-gtnext topPtr
• topPtr location

X C L
B
location
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Implementing Push

• templateltclass ItemTypegt
• void StackTypeltItemTypegtPush ( ItemType newItem
  )
• // Adds newItem to the top of the stack.
• if (IsFull())
• throw PushOnFullStack()
• NodeTypeltItemTypegt location
• location new NodeTypeltItemTypegt
• location-gtinfo newItem
• location-gtnext topPtr
• topPtr location

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Using operator delete

• The object currently pointed to by the pointer is
  deallocated, and the pointer is considered
  unassigned. The memory is returned to the free
  store.

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Deleting item from the stack

• NodeTypeltItemTypegt tempPtr
• item topPtr-gtinfo
• tempPtr topPtr
• topPtr topPtr-gtnext
• delete tempPtr

B X C L
tempPtr
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Deleting item from the stack
item
B

• NodeTypeltItemTypegt tempPtr
• item topPtr-gtinfo
• tempPtr topPtr
• topPtr topPtr-gtnext
• delete tempPtr

B X C L
tempPtr
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Deleting item from the stack
item
B

• NodeTypeltItemTypegt tempPtr
• item topPtr-gtinfo
• tempPtr topPtr
• topPtr topPtr-gtnext
• delete tempPtr

B X C L
tempPtr
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Deleting item from the stack
item
B

• NodeTypeltItemTypegt tempPtr
• item topPtr-gtinfo
• tempPtr topPtr
• topPtr topPtr-gtnext
• delete tempPtr

B X C L
tempPtr
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Deleting item from the stack
B
item

• NodeTypeltItemTypegt tempPtr
• item topPtr-gtinfo
• tempPtr topPtr
• topPtr topPtr-gtnext
• delete tempPtr

X C L
tempPtr
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Implementing Pop

• templateltclass ItemTypegt
• void StackTypeltItemTypegtPop ( ItemType item )
• // Removes element at the top of the stack and
• // returns it in item.
• if (IsEmpty())
• throw PopOnEmptyStack()
• NodeTypeltItemTypegt tempPtr
• item topPtr-gtinfo
• tempPtr topPtr
• topPtr topPtr-gtnext
• delete tempPtr

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• templateltclass ItemTypegt
• bool StackTypeltItemTypegtIsFull( ) const
• // Returns true if there is no room for another
  NodeType // node on the free store false
  otherwise.
• NodeTypeltItemTypegt location
• try
• location new NodeTypeltItemTypegt
• delete location
• return false
• catch(bad_alloc exception)
• return true

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• // Alternate form that works with older compilers
• templateltclass ItemTypegt
• bool StackTypeltItemTypegtIsFull( ) const
• // Returns true if there is no room for another
  NodeType // node on the free store false
  otherwise.
• NodeTypeltItemTypegt location
• location new NodeTypeltItemTypegt
• if ( location NULL )
• return true
• else
• delete location
• return false

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Why is a destructor needed?

• When a local stack variable goes out of scope,
  the memory space for data member topPtr is
  deallocated. But the nodes that topPtr points to
  are not automatically deallocated.
• A class destructor is used to deallocate the
  dynamic memory pointed to by the data member.

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• templateltclass ItemTypegt
• void StackTypeltItemTypegtMakeEmpty( )
• // Post Stack is empty all elements
  deallocated.
• NodeTypeltItemTypegt tempPtr
• while ( topPtr ! NULL )
• tempPtr topPtr
• topPtr topPtr-gtnext
• delete tempPtr
• templateltclass ItemTypegt
• StackTypeltItemTypegtStackType( ) // destructor
• MakeEmpty( )

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• templateltclass ItemTypegt
• void QueTypeltItemTypegtDequeue( ItemType item )
• // Removes element from from front of queue
• // and returns it in item.
• // Pre Queue has been initialized.
• // Queue is not empty.
• // Post Front element has been removed from
  queue.
• // item is a copy of removed element.
• NodeTypeltItemTypegt tempPtr
• tempPtr qFront
• item qFront-gtinfo
• qFront qFornt-gtnext
• if ( qFront NULL )
• qRear NULL
• delete tempPtr

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