2. Teaching design techniques to design efficient solutions to problems
National 5
Computing Science
Teaching design techniques to design efficient solutions to problems

3. Aims to link computational thinking with design
to look at approaches to teaching design

4. Computational Thinking
The thinking that is undertaken before starting work on a computer.
It describes the process and approaches we draw on when thinking about problems in such a way that a computer can help us.

5. Decomposition Breaking down of a problem into smaller parts.
solving smaller problems is easier
solving of the problem can then be shared
Decomposition can be applied to all types of day to day problems.
Leads naturally to modularity.

6. Brainstorming Choose destination Book flights
Annual leave permission from boss
Preparing for a holiday
Book hotel
Choose dates
Get currency
Although we have split the problem into smaller chunks we now need to organise it into a logical order.

7. Why is the order important ? Some things may be dependant on others
Choose destination
Choose Dates
Annual Leave permission from boss
Book Flights
Book Hotel
Get currency
P e r f e c t S c e n a r i o
Bremen
10th – 16th October
Booked with Bookingmyholiday.com
Change pounds to Euros
Yes
Booked with Ryanair
Unfortunately life isn’t always smooth!

8. What we have here is a loop
Annual Leave permission from boss
Choose destination
Choose Dates
Repeat until boss gives permission
Choose Dates
Bremen
10th – 16th October
No !
15th to 21st October
No !
5th to 10th November
Yes

9. Suggested decomposition lessons
Candidates brainstorm a problem then work together in pairs to produce a logical sequence of steps.
Candidates are given a sequence of steps (preferably cut out blocks) that are not in the correct order and working together in pairs put them into a correct sequence.

10. Algorithms What we have been creating is called an algorithm.
An algorithm is a sequence of instructions or rules to get something done.
This is how we can design solutions that we can code computers to solve.
We use algorithms in other areas of life eg
recipes for cooking
directions for getting to places
diagnosing patients
There are different ways of representing algorithms.

11. Structure diagrams
Show the solutions to problems using only 3 types of construct
Process such as a calculation
Loop where part of the problem repeats a fixed number of times or repeats until conditions are met
Selection where the problem may branch depending on the conditions met

12. The structure diagrams are read from the top down and from left to right.
If your numbers are 2, 4 ,7, 1 and 6 what is displayed?
Can you use this algorithm to find the average of 10 numbers?

13. This algorithm calculates interest for a loan
Total = £ 2140
What would the output be if you wanted to borrow £ 2,000
Loan = £ 30000
Interest =£ 1500
Total = £ 31500
What would the output be if you wanted to borrow £ 30,000
What would the output be if you wanted to borrow £ 10,000
Loan = £ 10000
Interest =£ 700
Total = £ 10700

14. This algorithm calculates the cost of carpeting a house
Fill in the blanks

15. Flow charts
Show the solutions to problems using a number of different symbols
Flow line shows the flow between symbols
Terminal represents the start and end of the process
Initialisation of a variable
Input/ Output of data
Decision where the problem may branch
Process such as a calculation
Used to split a flowchart up it it’s too big for the page

16. A flow chart starts from the top and works it’s way down following the flow of the arrows.

17. What problem is this flowchart solving?
What output would you have if the ages that were typed in from the keyboard were 32, 17, 25, 24, 39, 65
What test data should you use to test this flowchart works?
Why do we set the age and counter to 0 initially?

18. Pseudocode
Is a kind of structured English for describing algorithms and is intended for human reading.
Pseudocode can look like code in an implemented problem but it doesn’t have the same strict syntax.
Most pseudocode uses
IF… THEN…ELSE.. Type statements for selection
Repeat… UNTIL Type statements for repetition
The design should begin by defining the main steps of an algorithm. Where a step of the algorithm requires refinement, a numbering system may be used to denote which line of the algorithm is being refined.
Identified selection and repetition in the problem, may be highlighted with indentation.

19. Calculating the volume of water in a swimming pool
Algorithm
1 Ask user to enter dimensions of a swimming pool in metres
2 Calculate volume of pool
3 Display message stating the volume of the pool
Refinement
1.1 Ask user to enter length of pool
1.2 Ask user to enter width of pool
1.3 Ask user to enter depth of pool
2.1 Volume is calculated as length times width times depth
3.1 Display “The volume of the pool is”, volume

20. What does this algorithm do?
Set answer to 77
Set guess to 0
Repeat
get guess
IF guess equals answer THEN
display Well guessed
ELSE
IF guess is greater than answer THEN
display Too High
display Too Low
END IF
UNTIL answer equals guess
What tests would you use to check that your algorithm worked?
The guess is only meant to be between 0 and 100.
How can we change the algorithm to limit the guess?
Alter the algorithm.

21. Set answer to 77
Set guess to 0
Repeat
get guess
IF guess<1 OR guess>100 THEN
display you must enter a number between 1 and 100
END IF
Until guess>0 AND guess <101
IF guess equals answer THEN
display Well guessed
ELSE
IF guess is greater than answer THEN
display Too High
display Too Low
UNTIL answer equals guess
We call this input validation
It is used in many programs where the user is restricted in what they should enter

22. Problem
Design a solution for deciding the category of a parcel using the following criteria:
small parcel has a maximum weight of 2kg
medium parcel has a maximum weight of 20kg
large parcel is anything heavier than 20kg
Get a partner to check that it works!

23. Flowchart Ask for the weight of the parcel Is the weight
<=2Kg
Yes
It’s a small parcel No
Is the weight >20Kg
It’s a Large parcel
Yes No
It’s a medium parcel

24. Structure diagram Ask for the weight Is the weight of the parcel
<=2Kg No
Yes
Is weight>20Kg
It’s a small parcel
Yes No
It’s a large parcel
It’s a medium parcel

25. Pseudocode Get weight of parcel If weight of parcel < =2 THEN
parcel size = small
ELSE
IF weight of parcel >20 THEN
parcel size = large
parcel size = medium
END IF

26. Suggested algorithm lessons
Give candidates an algorithm and ask them to check that it works. This can lead into testing and shows that test data tables can be created at the design stage and then used again at the testing stage.
Give candidates a problem solved using different design techniques and get them to check that they all solve the same problem (one could be slightly wrong)
Give candidates an algorithm and a variety of inputs and ask them to say what the output would be.
Get candidates to match different problem descriptions to completed designs.

27. Patterns and Generalisation
By identifying patterns we can:
make predictions
create rules
solve more general problems
create code that makes efficient use of coding constructs

28. Let’s design a solution that creates the following pattern

29. Here is my pseudocode
Move forward 100
Turn right 90 degrees
Turn right 45
Move forward 100
Turn right 90 degrees
Turn right 45
Move forward 100
Turn right 90 degrees
Turn right 45
Move forward 100
Turn right 90 degrees
Turn right 45

30. We quickly see that the following is repeated 8 times
So we can then re-write the
solution using a loop
Repeat 8 times
Move forward 100
Turn right 90 degrees
Turn right 45
End loop
Move forward 100
Turn right 90 degrees
Turn right 45
It helps if we can recognise patterns at the start of the design process

31. We can see that there is a further repetition
So we can then re-write the
solution using another loop
Repeat 8 times
Move forward 100
Turn right 90 degrees
Turn right 45
End loop
Repeat 8 times
Repeat 4 times
Move forward 100
Turn right 90 degrees
End loop
Turn right 45
I would have started to talk about a procedure for the drawing of the square at this point.

32. Write an algorithm that simulates access to a cash machine where you get 3 attempts to enter the correct PIN.
Does it work?
Is there a pattern?
Can you make it more efficient ?
Try Re-writing
the structure diagram

33. We have to initialise the counter to 0 at the start
We have to have an action if the PIN isn’t correct after 3 attempts
We have to use a counter to keep track of how many opportunities we give the user to get the PIN

34. Write an algorithm that simulates a code activated door system in a hotel where guests are given three opportunities to put in the correct code to open their room.
Does it work?
Is there a pattern?
Can you make it more efficient ?
Try Re-writing
the flowchart

35. We have to initialise the counter to 0 at the start
We have to have an action if the PIN isn’t correct after 3 attempts
We have to use a counter to keep track of how many opportunities we give the user to get the PIN

36. Is there some redundancy in this algorithm?
This algorithm simulates security access where only the users Staff and Admin have access.
Is there some redundancy in this algorithm?
Do we need to ask this?

37. The algorithm is a little simpler
This version does the same task but without the early opt out if the User ID is wrong
The algorithm is a little simpler

38. Summary Before using a computer use your brain – it’s more powerful!
take a problem
decompose it into smaller parts
write an algorithm
is it efficient?
does it work? Test it
Now you can start to code
For more information on computational thinking see the Computing at School guide