Developing Flowcharts

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Developing Flowcharts

• Putting algorithms to work

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What is a flowchart?

• Flowcharts are one method for creating an
  Algorithm.
• They allow a process to be described in a
  step-by-step manner.
• Other Algorithm types are Pseudocode and Prose.

3
Terminators

• Oval Shape
• One line in or out
• Used to indicate the beginning and end of a
  process

4
Data Boxes

• Parallelogram shaped
• One line in, One line out
• Used to indicate the input or output of data from
  the system.

5
Process Boxes

• Rectangle shaped
• One line in, One line out
• Used to indicate a process step

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Decision Boxes

• Diamond shaped
• One line in, two lines out
• Must contain a binary question (Yes/No,
  True/False, 0/1, etc)
• Used to branch a program dependent upon a
  condition being met

7
Subprocess Box

• Rectangle shaped, with bars on the sides
• One line in, One line out
• Used to include a predefined process

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Simple Flowchart

• This chart indicates a typical example of Input,
  Process, Output

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Three basic structures

• All flowcharts are composed of three basic
  control structures
• Sequence
• Decision
• Repetition

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Sequence

• Events happen one after the other, with no
  branching
• Flow is directly from top to bottom

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Decision

• Uses a decision box to branch to one of two
  options
• Flow is downwards
• Lines rejoin the flow at lines, NOT boxes.

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Repetition

• Used to repeat a process, or wait until a
  condition is met before proceeding.
• Flow is upwards.
• Lines join at lines, NOT boxes.

13
Getting started

• Start by identifying and drawing the simplest
  flow from beginning to end.
• Chart this process from top to bottom.
• Account for the uncovered decisions.
• Check all boxes have the right number of in/out
  lines.
• Check for any edge cases.

14
Bad design

• What is wrong with this chart?
• The box has two lines in, one line out
• Lines must join other lines, never boxes!

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Bad design

• What is wrong with this flowchart?
• Never use curved lines.
• Always straight
• Always vertical or horizontal.

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Remember

• Drawing flowcharts is actually easy.
• Breaking tasks into small steps is often much
  harder than it might seem.
• If you can flowchart it, you can program it.