Modular flowcharts

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Modular flow-charts
Applied Computing AC1101
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Selection

• Choose to perform an action or not perform it
• Choose to perform an action or otherwise do
  something else
• Choose to perform one of a set of possibilities

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Repetition

• Do something a fixed number of times
• Do something until something becomes true
• While something is true, do something

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Getting into detail

• Advantages of structure diagrams
• Show overall structure of solution
• Clearly identify individual modules
  (functions?)and relationships between them
• Limitations
• Clumsy for showing selection repetition
• Sometimes easier to understand solution as a flow
  of events and actions than as a structure

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Modular flowcharts

• Symbols to show events and actions
• All symbols connected by lines
• Lines show allowable actions at any point
• Modular flowcharts have only one way in and one
  way out
• Modules have only one entranceand one exit point

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Flowchart symbols
Note rounded edges
Terminator
Action boxor module
Selection
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Sequence
Time
No need tosay anything here -Its obviously the
end
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Selection boxes
Selection box can have two lines coming out, one
for if the condition is true, the other for false
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Selection (1)
if the condition is true, do Things to do,
otherwise miss it out
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Selection (2)
if the condition is true, do Things to do, or
else do Other things to do
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Selection (3)
if condition 1 is true, do Something, or else if
condition 2 is true do Other thing, or else do
Default
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Repetition (1)
Do these things again and again ...
until this condition has been met
Always does Things to do at least once
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Repetition (2)
Only does Things to do while the condition is
true ... so may not do Things to do at all
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Top-down design using flowcharts

• Modules must have only one entry and one exit
  point
• So nesting becomes possible
• Helps to identify functions
• And so on

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Nesting of top-down design
Nesting of modules is easybecause of the
ruleone line in, one line out
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Example 1
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Example 2
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Example 3
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Exam marks example

• We have the marks from sixty students who have
  sat an exam.
• We want to know how many students have passed and
  how many have failed
• The pass mark is 50

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Example to work out

• A survey has been carried out to count the number
  of vehicles crossing the Tay Bridge.The number
  of cars crossing during each hour is recorded,
  giving 24 counts per day.
• Draw a modular flowchart for a program which
  reads the counts for one day and produces an
  output giving the total number of vehicles
  crossing during the day and the maximum number
  crossing in one hour.
• If time, calculate total income for the day (each
  vehicle pays 80p) and average vehicles per hour
• Can you identify candidates for separate
  functions?

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Summary - modular flowcharts

• Good way to show flow of program,especially
  selection and repetition
• Because only one entrance and exit allowed, very
  good for representing stepwise refinement
• Helps to identify functions
• Good for checking correctness of solutions