Stack ADT

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Stack ADT

• IC312
• A Linear Data Type

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Stack ADT

• Stack might bring to mind something like this

What can we do to a stack like this?
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Stack ADT Operations

• Things we can do with a stack
• Add entries to the top
• Remove from the top
• Display top entry
• Display ALL entries
• Get size of Stack
• Find out if Stack is empty

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Stack ADT Assumptions

• Given the operations (behaviors) what are the
  assumptions/restrictions on the data?
• All data is of same type
• Data is in some specific order
• First added at bottom, last at top
• What assumptions have we made about data storage?
• Relative order of data is maintained

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Stack ADT

• We can think of our list like this

Top
OR this
where the last thing we put on the top is the
first thing we pull out
Bottom
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Specifications (modifiers)

• Push (add)
• Adds element to top of stack unless stack is full
• Returns nothing
• Pop (remove)
• Removes element from top of stack unless stack is
  empty
• Returns element from top

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Specifications (accessers)

• Top
• Returns element from top of stack
• getSize
• Returns number of elements in stack
• isEmpty
• Returns true if stack is empty

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Adding Entries

• We always add to (push onto) top

Top
Bottom
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Removing Entries

• We always remove from (pop from) top

Top
Bottom
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Different Situations

• We must consider different possible situations
• For Example
• Is pushing onto an empty stack different than a
  populated stack?
• What about popping?

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Problem Situations

• We must address potential problem situations
• Popping from an empty stack is meaningless
• Displaying the top of an empty stack is
  meaningless
• What if stack has a fixed size and is full?

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Interface

• Defines methods a class must implement

interface StackltEgt bool push(E entry) E
pop() E top() int getSize() bool
isEmpty()
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Implementation

• Must implement all methods in interface
• Need underlying data structure Something to
  hold the data
• Can use array or list

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Uses

• Keeping track of jobs
• In order to do x you first have to do y, but
  before that you have to do z
• Keeping track of past events
• undo and back
• Post-fix expression evaluation
• Checking for parentheses balance