Flowcharts

1
Flowcharts

• adapted from
• A Visual Tool for Logic Design and Program
  Planning,
• by Dr. Donald Bell,
• Cal Poly, 1999
• updated April, 2010

2
What Is a Flowchart?

• Diagram with lines (arrows) and symbols to show
  how something works
• can show how code works in a program
• definition and symbols (programming)
• can also be used to help understand other
  processes
• criminal justice system flowchart (symbols
  somewhat different than for programming)

3
Flowcharts

• Reasons for using flowcharts
• similar to reasons for using pseudocode
• Special symbols used in flowcharts
• Rules for Successive Refinement

4
Purpose of Flowcharts

• To plan your logic prior to writing your program
• Can be very helpful when you have complex
  conditional logic (the graphics help visualize
  the logic flow)
• Assists in applying "successive refinement" ("top
  down" analysis)
• Can also be used to document your logic
• not used as much with object oriented code

5
Successive Refinement

• Equally applicable whether you use flowcharting
  or pseudocode
• Start at the very "top level"
• a one line statement of your program's purpose
• break it down by stages into greater and greater
  levels of detail
• Successive refinement stops when there is enough
  detail to write the program
• Each flowchart symbol is a basic building block
  (like Tinker Toys or Lego blocks)
• these are assembled into complex structures
• assembled in specific ways

6
Flowcharting Symbols

• Like pseudocode there are no fixed "standards",
  but there are conventions
• Flowcharts use ovals, rectangles and diamonds
• ovals start and end the logic flow
• rectangles are for imperative statements
• diamonds are for decisions
• Some people use other symbols such as
  parallelograms for input and output, etc.

7
Rules for Applying Successive Refinement Using
Flowcharts

• Can replace one rectangular block with several
  more detailed ones
• Can replace a rectangular block with one
  including logic or iteration (looping)
• Each block has one entry point, and one exit
  point (very important!)
• but different statements can enter it there
• Flow does not terminate until you get to a stop
  or end symbol

8
Rules for Applying Successive Refinement Using
Flowcharts - 2

• Start with a simple chart that summarizes the
  whole system (high level view)
• use separate symbols for each major aspect, e.g.,
  input, processing, output
• Decompose each major aspect into a more detailed
  flow chart
• e.g., input could decompose into prompt user,
  read input, check input, if wrong give error
  message and prompt for good data

9
Flowcharts OO Programs

• Flowcharts use a sequential logic
• top to bottom
• OO programming is often "event driven"
• objects fire methods in response to messages
• However flowcharting is suitable for developing
  code within methods

10
UML Diagrams

• Identify tasks (use cases)
• Identify which object should handle a task
• Identify messages sent between objects
• Draw objects and messages into a diagram
• example of a "use case diagram (which shows a
  class, properties, methods)

11
Review

• Draw flowcharts for sequence, selection and
  iteration control structures
• Draw a flowchart for code that counts the number
  of students with GPAs of 3.0 or higher and then
  prints the total
• Will need to use sequence, selection and
  iteration