Problem Solving: Structure Charts

UNIT 1 - ⇑ Problem Solving ⇑
← Top-down design and Step-wise refinement	Structure charts	Decision tables →

A Structure Chart in software engineering is a chart which shows the breakdown of a system to its lowest manageable parts. They are used in structured programming to arrange program modules into a tree. Each module is represented by a box, which contains the module's name. The tree structure visualizes the relationships between modules, showing data transfer between modules using arrows. Structured Charts are an example of a top-down design where a problem (the program) is broken into its components. The tree shows the relationship between modules, showing data transfer between the models.

Symbol

Name

Meaning

Module Name

Process

Each Box represents a programming module, this might be something that calculates the average of some figures, or prints out some pay slips

Data Couple

Data being passed from module to module that needs to be processed.

Flag

[Extension - you don't need to know this for the exam] Check data sent to process to stop or start processes. For example when the End of a File that is being read is reached, or a flag to say whether data sent was in the correct format

Let's take a look at a simple example of how this might be executed when representing the following code:

dim num1, num2 as integer

sub calculateAverage()
  dim avg as integer
  inputNums()
  avg = average(num1, num2)
  outputAvg(avg)
end sub

function average(a,b)
  return (a + b) / 2
end function

sub inputNums()
  num1 = console.readline()
  num2 = console.readline()
end sub

sub outputAvg(x)
  console.writeline("average = " & x)
end sub

Exercise: Structure Charts

Create structure charts for the following code:

sub main()
  dim num1 as integer
  dim num2 as integer
  dim avg as integer
  sayHello()
  num1 = 34
  num2 = 89
  avg = average(num1, num2)
end sub

function average(a,b)
  return (a + b) / 2
end function

sub sayHello()
  console.writeline("hello")
end sub

Answer:

Selection edit

Structure Chart representation of the selection code

A selection in a Structure Chart is determined by the diamond symbol. This means a condition will be checked and depending on the result, different modules will be executed.

sub main()
  dim num1 as integer
  num1 = console.readline()
  if num1 = 7 then
     luckyNumber()
  else
     otherNumber()
  endif
end sub

Iteration edit

Structure Chart of the code to the left

Using the semi circular arrow we can represent iteration in Structure Charts. The arrow encompasses a link to a module, implying that module is executed multiple times. Let's take a look at a coded example:

sub main()
  dim num1 as integer
  num1 = console.readline()
  while num1 > 0 do
     num1 = countdown(num1)
  end while
end sub

Function countdown(a)
  return a - 1
End Function

Exercise: Structure Charts, Iteration and Selection

Create structure charts for the following code:

sub howManyThrees()
  dim num1, count, total as integer
  num1 = startMsg()
  count = 0
  total = 0
  while num1 > 0 do
     checkNumber(count, total, num1)
     num1 = num1 - 1
  end while
  endMsg(count)
end sub

sub checkNumber(byRef c, byRef t, byVal n)
  If n MOD 3 = 0 Then
     c = divBy3(c)
  Else
     t = add(n, t)
  EndIf
end sub

function divBy3(x)
  return x + 1
end function

function add(n, t)
  return n + t
end function

function startMsg()
  console.writeline("program started, enter your number")
  return console.readline()
end function

sub endMsg(n)
  console.writeline("number of threes : " & n)
end sub

Answer: