The Origins of

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The Origins of Algorithm
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The Origins of the Term Algorithm
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Developing Algorithm Using Stepwise Refinement

• Read the problem statement carefully
• Rewrite it in your own words if it is not clear
• Highlight the nouns and look for data items
• Highlight the verbs to determine the work that
  needs to be done
• Write the initial algorithm that just describes
  the inputs, outputs and work to be done

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Stepwise Refinement

• Now go back to each step in the initial algorithm
  and refine it to describe how it will be
  implemented
• The Key steps are
• Rewrite the statement if not clear
• NounsgtData, VerbsgtAction
• Initial Algorithm(WHAT)
• Final Algorithm(HOW)

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Algorithm Development Exercise

• Problem 1
• A Sunoco gas station offers 5 cents per gallon
  discount each Sunday. If a person fills up 20
  gallons every week, how much money will that
  person save in X weeks?

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Algorithm Development Exercise

• Problem 2
• Given the radius of a circle, develop an
  algorithm that computes the area and circumference

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Algorithm Development Exercise

• Problem 3
• Write a cash register algorithm that will compute
  7 percent sales tax at the price of an item and
  then add the tax to the price to obtain the final
  price

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Properties of Algorithms

• Simplicity
• Precision
• Various Levels of Abstraction

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Algorithms

• Algorithms specify the behavior
• Programs in specific languages just express the
  algorithm in one particular form

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Information

• Information means knowledge about something
• Data is a specific representation of information

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Components of An Algorithm

• Data Structures
• Data Manipulation Instructions
• Conditional Expressions
• (if price greater than my_limit then dont buy)
• Control Structures
• (while (condition) do statement
• Modules

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Levels of Abstraction

• Details are HIDDEN if we use TOP DOWN approach to
  describe algorithms
• Example Counting names that begin with A in a
  list of names

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Recap

• What is the advantage of hiding details at the
  initial level of algorithm development?
• What properties of an object must be known to us
  before we can use it?
• How can we make software reusable?
• How many types of statements can be part of an
  algorithm?