CS 3358 Data Structures

1
Introduction

• CS 3358 Data Structures

2
What is Computer Science?

• Computer Science is the study of algorithms,
  including their
• Formal and mathematical properties
• The logic used to prove that we have the correct
  solutions
• Hardware realizations
• Creating microchips, processors, and other
  hardware
• Linguistic realizations
• Creating the languages to express the algorithms
  precisely
• Applications
• The actual real-life problems that are solved

3
Software Engineering

• Goal
• Production of software that is effective and
  reliable, understandable, cost effective,
  adaptable, and reusable
• Because of the long lifetime many people will be
  involved
• Creation
• Debugging
• Maintenance
• Enhancement
• Two-thirds of the cost is typically beyond
  creation

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Design Principles

• Abstraction
• Encapsulation
• Modularity
• Hierarchy

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Principles

• Determine the relevant properties and features
  while ignoring nonessential details

• Abstraction
• Encapsulation
• Modularity
• Hierarchy

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Principles

• Separate components into external and internal
  aspects

• Abstraction
• Encapsulation
• Modularity
• Hierarchy

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Principles

• Construct a system from
• components and packages

• Abstraction
• Encapsulation
• Modularity
• Hierarchy

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Principles

• Ranking or ordering of objects

• Abstraction
• Encapsulation
• Modularity
• Hierarchy

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Abstract Data Types (ADT)

• A specification of a set of data and the set of
  operations that can be performed on the data.
• Independent of concrete implementation
• Uses defined interface
• Hides details from the user (information hiding)
• Not the same as a data structure

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ADT Example -- Stack

•  bool empty()
• Tests if this stack is empty.  
• E peek()
• Looks at the object at the top of this stack
  without removing it from the stack.
• E pop()
• Removes the object at the top of this stack and
  returns that object as the value of this
  function.  
• push(E item)
• Pushes an item onto the top of this stack.

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Why?

• Allows implementation to be changed without
  violating ADT definitions
• Gives a standard list of structures to use and
  study
• Building blocks and tools
• Foundation for OOP
• Abstraction, Encapsulation, Modularity, Hierarchy

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Object-Oriented Design

• Purpose
• Promote thinking about software in a way that
  models the way we think and interact with the
  physical word
• Including specialization
• Object
• Properties or attributes
• Behaviors

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Programming

• Class
• Term for a type of software object
• Object
• An instance of a class with
• specific properties andattributes

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Programming

• Problem solving through the use of a computer
  system
• Maxim
• You cannot make a computer do something if you do
  not know how to do it yourself

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Problem Solving Process
Determine
Analysis
problem features
Rethink as
appropriate
Describe objects
Design
and methods
Produce the
Implementation
classes and code
Examine for
Testing
correctness
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Tips

• Find out as much as you can
• Reuse what has been done before
• Expect future reuse
• Break complex problems into subproblems

Find out what is known about the problem Talk to
the presenter Determine what attempts have
succeeded and what attempts have failed
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Preconditions and Postconditions

• Frequently a programmer must communicate
  precisely what a function accomplishes, without
  any indication of how the function does its work.

Can you think of a situation where this would
occur ?
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What are Preconditions and Postconditions?

• One way to specify such requirements is with a
  pair of statements about the function.
• The precondition statement indicates what must be
  true before the function is called.
• The postcondition statement indicates what will
  be true when the function finishes its work.

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Example
void write_sqrt( double x) // Precondition x
gt 0. // Postcondition The square root of x
has // been written to the standard output.
...
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Example
Which of these function calls meet the
precondition ?
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Always make sure the precondition is valid . . .

• The programmer who calls the function is
  responsible for ensuring that the precondition is
  valid when the function is called.

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. . . so the postcondition becomes true at the
functions end.

• The programmer who writes the function counts on
  the precondition being valid, and ensures that
  the postcondition becomes true at the functions
  end.

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On the other hand, careful programmers also
follow these rules

• When you write a function, you should make every
  effort to detect when a precondition has been
  violated.
• If you detect that a precondition has been
  violated, then print an error message and halt
  the program...
• ...rather than causing
• a disaster.

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Example
void write_sqrt( double x) // Precondition x
gt 0. // Postcondition The square root of x
has // been written to the standard output.
assert(x gt 0) ...
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Advantages of Using Preconditions and
Postconditions

• Succinctly describes the behavior of a
  function...
• ... without cluttering up your thinking with
  details of how the function works.
• At a later point, you may reimplement the
  function in a new way ...
• ... but programs (which only depend on the
  precondition/postcondition) will still work with
  no changes.