Lecture 3
Structure charts revision
Four components

module

sequences
iterations
selections


A sequence of operations is represented by boxes connected with lines. In the example
below, module A consists of the sequence of modules B, C and D.
A sequence
An iteration is again represented with joined boxes. In addition the iterated operation has
a dot on top of the box. In the example below, module A consists of an iteration of zero
or more invocations of module B.
An iteration
Selection is similar to a sequence, but with a diamond. In the example, module A consists
of one and only one of operations B, C or D.
A
B
C
D
The IPO Chart (p46)
This extends and organises the information in the problem analysis chart. It shows in
more detail what data items are input, what processing takes place on the data and what
information will be the end result, the output.
In the IPO chart the output is the first to be completed and then the input and then the
processing.
Input
All input data (from
section 1 of the
Problem Analysis
chart)
Processing
All processing in
steps (from Sections
3 and 4 of the
problem analysis
chart)
Module Reference
Module reference
from the structure
chart
Output
All output
requirements (from
sections 1 and 2 of
the problem analysis
chart)
Read first number
Read second
number
Read third number
Calculate the
average of the three
numbers
Print the average
Average
TASK :- 1)
Construct an IPO
Chart for the
Average Problem
2) And for the
Gross Pay problem
Enter 3 numbers
1. Enter three
numbers
2. calculate the
average of
the three
numbers
3. print the
average
4. end
Writing Algorithms
After using the structure chart and the IPO chart the next step in organising the solution is
to for the programmer to develop a set of instructions for the computer – called
algorithms or Psuedocode.
An algorithm is set of instructions needed to solve the problem
- need to write a separate set of instructions for each module in the structure chart.
- the control module uses end because its the end of processing
- the other modules use exit because the processing continues
Some Programming concepts
Relational Operators :- >
<
=
!=
>=
<=
greater than x > y
less than
x<y
equals
x==y
not equals
x != y
is greater than or equal to x >= y
is less than or equal to x <= y
Conditional logic – if then else
Task 1) – write a pseudocode / algorithm to work out what grade a student got
based on the following information :- if student (above or equal) to 90 – A , 80 – B,
70 – C, 60 – D, less then or equal 60 – F
If students grade is greater than or equal to 90
Display ‘A’
Else
If students grade is greater than or equal to 80
Display ‘B’
Else
If students grade is greater than or equal to 70
Display ‘C’
Else
If students grade is greater than or equal to 60
Display ‘D’
else
Display ‘f’
TASK 2)
1) Write Java code to ask user to enter their name and display it
2) Write Java code to ask user to enter two numbers and workout the average
Algorithms to Flowcharts
•
•
•
•
•
•
From algorithms the programmer develops
flowcharts
Graphical representations of algorithms
A flowchart shows the flow of processing form
beginning to end
Each block in flowchart represents one
instruction from an algorithm
Flowlines indicate direction of data flow
Why use flowcharts?
–
–
Flowcharts show errors in logic
A set if data can be tested easily using flowcharts
Flowchart Symbols (p78)
Start / End/ Exit
Enter data (e.g form from keyboard ) or
Write to printer or screen
Variable = expression Assign value of the
following expression to a variable location
Execute the instructions in named module
and then return to execute the next
instruction
Tasks
•
Conditional logic – if then else and loops
•
Task – Write a Flowchart and Algorithm
for Average Problem
•
•
Write a Flowchart and Algorithm for
Gross- pay problem
For each module in the Gross-pay
problem – write a flowchart and algorithm
control
Algorithm
Read
Calculate
Average
Print
End
1. Process Read
2. Process Calculate the
average of the three
numbers
3. Process Print the
average
control
Algorithm
Read
Control Module
•
•
•
•
•
•
•
Calculate
Print
false
Until
noMoreEmployees
true
End
Repeat
Process Read
Process Calc
Process Print
Until
NoMoreEmployees
End
Read
Read Hours,
PayRate
exit
Read
Module
1. Read
Hours,
Payrate
2. Exit
Calc
GrossPay
= Hours *
Payrate
Print
Print PayRate
exit
Calc Module
1.GrossPay =
HoursWorked *
PayRate
2.Exit
exit
Print Module
•
•
Print Pay
Exit
Systems Flow Charts
Used to document current flows showing where operations take place. The
analyst uses flowcharts to describe the processes in the system in pictorial form,
making the system easier to understand.
Used to document current flows showing where operations take place. The
analyst uses flowcharts to describe the processes in the system in pictorial form,
making the system easier to understand.
 The flowchart generally describes processes, files, input and output devises.
 Split the chart into columns representing different departments/locations and
staff associated with the system
 Flow is normally from top left to bottom right
 Use arrows to indicate direction of flow
No one correct solution
Scenario
There are three musical concerts taking place in the U.S.A raising money for
charity. In order to keep track of ticket applications, customers wishing to
purchase a ticket are requested to fill a form. Once a application for a ticket is
received by the office, the booking details are checked as is the availability of
spaces. If a place is available, details are recorded and customer informed.
Draw a flow chart demonstrating the above
Customer
Booking Office
Fill
applicati
on form
Customer
Check
application
form and
booking dates
Concert
Schedule
Check
availability of
concert seats
Y
Concert
Full?
Inform
cust
N
Send
cust
Ticket
s
Record
Concert
booking
place
Update
booking
file
MAKE NOTES Pages 130, 131, 133, 135, 136, 139, 140, 142
A Patient rings a doctor’s surgery to book an appointment. The receptionist takes patient
details and checks to see if the patient exists on their system. If the patient does not exist
on the system then the receptionist adds the patient to the system. If patient exists on the
system then receptionist checks next available appointment and informs patient of
appointment dates
1) Draw a Systems Flowchart
2) Write a Programming flowchart to work out the number of patients in the doctor
surgery. Consider which variable you need to use and which loop condition you
will use