Lect 3P. 1

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Structured Engineering Problem Solving and Logic
Diagrams

• Lecture 3

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TOOLS FOR PROGRAM DEVELOPMENT

• A variety of tools and techniques can be used in
  the process of program development
• Useful for organizing the tasks in problem
  solving
• Many of the tools are focused on the
• development or formulation of algorithms
• representation of algorithms
• refinement or structuring of algorithms

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TOOLS FOR PROGRAM DEVELOPMENT

• Top-down design technique
• Start with overall function and perform several
  step-wise refinements
• Pseudo code
• Artificial and informal language that helps
  programmers develop algorithms
• Logic diagrams
• Alternate representations of algorithms including
  graphic and state representations

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TOP-DOWN STEPWISE REFINEMENT

• Begin with a single statement that conveys the
  overall function of the program. This is a
  complete (but simple) representation of the
  program.
• Divide this "top" statement into a series of
  smaller tasks and list them in the order in which
  they must be performed to produce a first
  refinement.

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TOP-DOWN STEPWISE REFINEMENT

• Next, refine each of the smaller tasks into yet
  smaller steps, defining specific "variables" as
  may be needed in this second refinement.
• Continue refinement until algorithm is fully
  developed.
• When combined with pseudo code, writing the
  program is normally straightforward.

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Top-Down Example

• The Problem
• The students in a class have taken their first
  quiz. The grades (in the range of 0 to 100) are
  available. Determine the class average on the
  quiz.
• Givens
• Grades, Possible range of legitimate grades.

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Top-Down Example (continued)

• Unknowns
• How many grades to be averaged?
• Assumptions
• A "grade" not in the range of expected grades
  could be used to indicate the that all of the
  legitimate grades have been entered. (Called
  "sentinel" or "flag".)

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Top-Down Example (continued)

• Using pseudo code, we begin by representing the
  top
• Determine the class average for the quiz

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Top-Down Example (continued)

• Next, perform the first refinement
• Determine the class average for the quiz
• Initialize variables
• Input, sum, and count quiz grades
• Calculate and print the class average

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Top-Down Example (continued)

• Next, refine each one of these smaller tasks
• Initialize variables
• Initialize a running total to zero
• Initialize a grade counter to zero

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Top-Down Example (continued)

• Input, sum, and count quiz grades
• Input the first grade
• While the user has not entered the "flag"
• Add this grade into the running total
• Add one to the grade counter
• Input next grade (possibly the "flag")

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Top-Down Example (continued)

• Calculate and print the class average
• If the grade counter is not zero
• Set the class average to the running
• total divided by the grade counter
• Print the average
• Else
• Print "No grades were entered"

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Handling Special Cases

• Notice that the top-down refinement example
  included the handling of a "special case".
• Many of you are aware of the special treatment
  that Windows gives to the extreme "special cases"
  (sometimes called the BSOD or Blue Screen of
  Death)

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Handling Special Cases
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Some Types of Logic Diagrams

• Flow Charts -- graphic representation of an
  algorithm
• an aid to writing the program
• no formal standards, but common guidelines
• Action Diagrams -- technique for diagramming of
  control structures of a program
• an outline of the computer application
• what things happen, when, where, how many times

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Characteristics of Flow Charts

• Useful tool in program development
• Not a complete description of program
• Not only tool to use
• Made before writing the program
• Program might differ from flowchart
• Only executable statements are shown
• Specific equations and tests not included
• Every main and sub-program is charted

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Flow Charting Symbols

• The commonly used flowcharting symbols follow
• Refer to Section 9 of the H192 "Class Notes" for
  a more complete description of the various
  flowcharting symbols normally used

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Flow Charting Symbols

• Begin or End a Procedure
• "Main Program"
  "Subprogram"
• Begin
• End

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Flow Charting Symbols

• Write to Screen
• Read from Keyboard

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Flow Charting Symbols

• Read from a File
• Read from a File with a Check for End-of-File

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Flow Charting Symbols

• Decision or Selection Structure
• General Processing

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Flow Charting Symbols

• Definite Loop
• Indefinite Loop

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Flow Charting Symbols

• On-Page Connectors
• Off-Page Connectors

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Flow Charting Symbols

• Call (or Invoke) a Subprogram

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Daily Assignment F2

• Problem
• There are a number of apples in a large box
  which must be sorted into baskets. An apple is
  either a "large red" one, a "small red" one, or a
  "green" one.
• Develop a flow chart or algorithm to solve the
  problem

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Daily Assignment F2

• Assumptions
• 1. There are 3 empty baskets present and they are
  labeled
• 1 large red, 2 small red, 3 green
• 2. There are counters of some sort present.
• 3. The person sorting is not color blind and can
  tell the difference between large and small
  apples.
• 4. Only these three kinds of apples are in the
  large box.

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Daily Assignment F2

• Are there any unknowns?
• Start with the overall problem
• Develop the steps to solve the problem