1. 1. Computational Thinking
A Level Computer Science

2. Chapter 1: Computational thinking
Computer science has produced many useful methodologies to make developing systems more reliable and less effort, e.g:
software engineering
modelling the real world
systems analysis
programming techniques and paradigms
Layering (e.g. TCP/IP)
pipelining.
These can be applied to more than just making computer systems.
A programming paradigm is a fundamental style of computer programming, serving as a way of building the structure and elements of computer programs. Imperative, Logical, Functional, Object-Oriented
Layering is the organization of programming into separate functional components that interact in some sequential and hierarchical way, with each layer usually having an interface only to the layer above it and the layer below it.
With Pipelining, the computer architecture allows the next instructions to be fetched while the processor is performing arithmetic operations, holding them in a buffer close to the processor until each instruction operation can be performed. The staging of instruction fetching is continuous. The result is an increase in the number of instructions that can be performed during a given time period.y, with each layer usually having an interface only to the layer above it and the layer below it.

3. Computational Thinking
A problem-solving approach makes use of such things as:
abstraction
decomposition
algorithms.
Pattern recognition

4. Abstraction
Abstraction is the process of filtering out – ignoring - the characteristics of patterns that we don't need in order to concentrate on those that we do. It is also the filtering out of specific details. From this we create a representation (idea) of what we are trying to solve.
Video

5. abstraction

6. Abstraction
Layers of abstraction allow efficient problem solving – focusing on one part of problem at a time. 
Examples of abstraction:
a variable
a data structure
a network address
layers in a network
a symbol on a map

7. Decomposition - Breaking Down problems
The breaking down of a problem into smaller parts that are easier to solve.
The smaller parts can sometimes be solved recursively; that is, they can be run again and again until that part of the problem is solved.

8. Task
Think of one example that can be solved using a tree hierarchy, and one example of a problem that can be solved using alternative pathways
Tree Hierarchy
Alternative Pathways
Pythagoras Theorem
Holiday bookings

9. Data Flow diagram

10. DFD (data flow diagrams) extension
Jump>>

11. Creating Data Flow Diagrams
Steps:
Create a list of activities
Construct Context Level DFD (identifies external entities and processes)
Construct Level 0 DFD (identifies manageable sub process )
Construct Level 1- n DFD (identifies actual data flows and data stores )
Check against rules of DFD

12. DFD Naming Guidelines External Entity  Noun Data Flow  Names of data
Process  verb phrase
a system name
a subsystem name
Data Store  Noun

13. Creating Data Flow Diagrams Lemonade Stand Example

14. Creating Data Flow Diagrams
Example
Steps:
The operations of a simple lemonade stand will be used to demonstrate the creation of dataflow diagrams.
Create a list of activities
Old way: no Use-Case Diagram
New way: use Use-Case Diagram
Construct Context Level DFD (identifies sources and sink)
Construct Level 0 DFD (identifies manageable sub processes )
Construct Level 1- n DFD (identifies actual data flows and data stores )

15. Creating Data Flow Diagrams
Example
Create a list of activities
Think through the activities that take place at a lemonade stand.
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product

16. Creating Data Flow Diagrams
Example
Create a list of activities
Also think of the additional activities needed to support the basic activities.
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor

17. Creating Data Flow Diagrams
Example
Create a list of activities
Group these activities in some logical fashion, possibly functional areas.
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labour

18. Creating Data Flow Diagrams
Example
Construct Context Level DFD (identifies sources and sink)
Create a context level diagram identifying the sources and sinks (users).
Context Level DFD
Sales Forecast
CUSTOMER
0.0
Lemonade System
EMPLOYEE
Order
Production Schedule
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
Product Served
Pay
Payment
Time Worked
Received Goods
Payment
Purchase Order
VENDOR

19. Creating Data Flow Diagrams
Example
Construct Level 0 DFD (identifies manageable sub processes )
Create a level 0 diagram identifying the logical subsystems that may exist.
Level 0 DFD
1.0
Sale
Sales Forecast
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
Customer Order
Product Ordered
CUSTOMER
Payment
2.0
Production
EMPLOYEE
Production Schedule
Product Served
Inventory
Received Goods
VENDOR
3.0
Procure-ment
Purchase Order
Order Decisions
Payment
Pay
Time Worked
4.0
Payroll

20. Creating Data Flow Diagrams
Example
Construct Level 1- n DFD (identifies actual data flows and data stores )
Create a level 1 decomposing the processes in level 0 and identifying data stores.
Level 1 DFD
CUSTOMER
Customer Order
Request for Forecast
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
ORDER
1.1
Record Order
1.3
Produce Sales Forecast
Severed Order
Payment
Sales Forecast
1.2
Receive Payment
PAYMENT

21. Creating Data Flow Diagrams
Example
Construct Level 1 (continued)
Create a level 1 decomposing the processes in level 0 and identifying data stores.
Level 1 DFD
Product Order
ORDER
2.1
Serve Product
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
Quantity Severed
RAW MATERIALS
Production Schedule
2.2
Produce Product
Quantity Used
INVENTORTY
Production Data
2.3
Store
Product
Quantity Produced & Location Stored

22. Creating Data Flow Diagrams
Example
Construct Level 1 (continued)
Create a level 1 decomposing the processes in level 0 and identifying data stores.
Level 1 DFD
Order Decision
PURCHASE ORDER
3.1
Produce Purchase Order
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
Quantity On-Hand
RAW MATERIALS
Quantity Received
Received Goods
3.2
Receive Items
RECEIVED ITEMS
Payment Approval
3.3
Pay Vendor
VENDOR
Payment

23. Creating Data Flow Diagrams
Example
Construct Level 1 (continued)
Create a level 1 decomposing the processes in level 0 and identifying data stores.
Level 1 DFD
Time Worked
TIME CARDS
4.1
Record Time Worked
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
Employee ID
EMPLOYEE
Payroll Request
4.2
Calculate Payroll
Unpaid time cards
PAYROLL
Payment Approval
4.3
Pay Employee
PAYMENTS
Payment

24. Process Decomposition
1.0
Sale
1.1
Record Order
1.2
Receive Payment
2.0
Production
2.1
Serve Product
2.2
Produce Product
2.3
Store
Product
0.0
Lemonade System
3.0
Procure-ment
3.1
Produce Purchase Order
3.2
Receive Items
3.3
Pay Vendor
4.0
Payroll
4.1
Record Time Worked
4.2
Calculate Payroll
4.3
Pay Employee
Context Level
Level 0
Level 1

25. DFD Example: Bus Garage Repairs
Buses come to a garage for repairs.
A mechanic and helper perform the repair, record the reason for the repair and record the total cost of all parts used on a Shop Repair Order.
Information on labour, parts and repair outcome is used for billing by the Accounting Department, parts monitoring by the inventory management computer system and a performance review by the supervisor.

26. DFD Example: Bus Garage Repairs (cont’d)
External Entities: Bus, Mechanic, Helper, Supervisor, Inventory Management System, Accounting Department, etc.
Key process (“the system”): performing repairs and storing information related to repairs
Processes:
Record Bus ID and reason for repair
Determine parts needed
Perform repair
Calculate parts extended and total cost
Record labor hours, cost

27. DFD Example: Bus Garage Repairs (cont’d)
Data stores:
Personnel file
Repairs file
Bus master list
Parts list
Data flows:
Repair order
Bus record
Parts record
Employee timecard
Invoices

28. Bus Garage Context Diagram
Mechanical problem
to be repaired
Fixed mechanical
problems
Supervisor
Helper
Bus Repair Process
System
Repair summary
Labor
List of parts used
Inventory Management System
Labor
Labor, parts cost details
Mechanic
Accounting

29. CSUB Burger’s Order Processing System
Draw the CSUB Burger’s context diagram
System
Order processing system
External entities
Kitchen
Restaurant
Customer
Processes
Customer order
Receipt
Food order
Management report

30. Decomposition and oo
A common way of breaking down a problem and functionality.

31. task
Questions 1-3 page 17

32. ALGORITHMS AND FLOWCHARTS
Sub topic

33. ALGORITHMS AND FLOWCHARTS
A typical programming task can be divided into two phases:
Problem solving phase
produce an ordered sequence of steps that describe solution of problem
this sequence of steps is called an algorithm
Implementation phase
implement the program in some programming language

34. Steps in Problem Solving
First produce a general algorithm (one can use pseudocode)
Refine the algorithm successively to get step by step detailed algorithm that is very close to a computer language.
Pseudocode is an artificial and informal language that helps programmers develop algorithms. Pseudocode is very similar to everyday English.

35. Algorithm
Example 1: Write an algorithm to determine a student’s final grade and indicate whether it is passing or failing. The final grade is calculated as the average of four marks.

36. Algorithm Input a set of 4 marks
Calculate their average by summing and dividing by 4
if average is below 50
Print “FAIL”
else
Print “PASS”

37. Algorithm Detailed Algorithm Step 1: Input M1,M2,M3,M4
Step 2: GRADE  (M1+M2+M3+M4)/4
Step 3: if (GRADE < 50) then
Print “FAIL”
else
Print “PASS”
endif

38. The Flowchart
(Dictionary) A schematic representation of a sequence of operations, as in a manufacturing process or computer program.
(Technical) A graphical representation of the sequence of operations in an information system or program. Information system flowcharts show how data flows from source documents through the computer to final distribution to users. Program flowcharts show the sequence of instructions in a single program or subroutine. Different symbols are used to draw each type of flowchart.

39. The Flowchart shows logic of an algorithm
A Flowchart
shows logic of an algorithm
emphasizes individual steps and their interconnections
e.g. control flow from one action to the next

40. Flowchart Symbols

41. Example Step 1: Input Q1,Q2,Q3,Q4 Step 2: GRADE  (Q1+Q2+Q3+Q4)/4
START
Input
Q1,Q2,Q3,Q4
GRADE(Q1+Q2+Q3+Q4)/4 IS
GRADE<50
PRINT
“FAIL”
STOP Y N
Step 1: Input Q1,Q2,Q3,Q4
Step 2: GRADE  (Q1+Q2+Q3+Q4)/4
Step 3: if (GRADE <50) then
Print “FAIL”
else
Print “PASS”
end if
PRINT
“PASS”

42. Example 2
Write an algorithm and draw a flowchart to convert the length in feet to centimeter.
Input the length in feet (Lft)
Calculate the length in cm (Lcm) by multiplying LFT with 30
Print length in cm (LCM)

43. Example 2 Flowchart Algorithm Step 1: Input Lft Step 2: Lcm  Lft x 30
Step 3: Print Lcm
START
Input
Lft
Lcm  Lft x 30
Print
Lcm
STOP

44. Example 3
Write an algorithm and draw a flowchart that will read the two sides of a rectangle and calculate its area.
Input the width (W) and Length (L) of a rectangle
Calculate the area (A) by multiplying L with W
Print A

45. Example 3 Algorithm Step 1: Input W,L Step 2: A  L x W
Step 3: Print A
START
Input
W, L
A  L x W
Print A
STOP

46. DECISION STRUCTURES The expression A>B is a logical expression
it describes a condition we want to test
if A>B is true (if A is greater than B) we take the action on left
print the value of A
if A>B is false (if A is not greater than B) we take the action on right
print the value of B

47. DECISION STRUCTURES is
A>B
Print B
Print A Y N

48. IF–THEN–ELSE STRUCTURE
The structure is as follows
If condition then
true alternative
else
false alternative
endif

49. IF–THEN–ELSE STRUCTURE
The algorithm for the flowchart is as follows:
If A>B then
print A
else
print B
endif is
A>B
Print B
Print A Y N

50. Relational Operators Operator Description Relational Operators >
Greater than
<
Less than ==
Equal to 
Greater than or equal to 
Less than or equal to !=
Not equal to

51. Example 4
Write an algorithm that reads two values, determines the largest value and prints the largest value with an identifying message.
Step 1: Input VALUE1, VALUE2
Step 2: if (VALUE1 > VALUE2) then
MAX  VALUE1
else
MAX  VALUE2
endif
Step 3: Print “The largest value is”, MAX

52. “The largest value is”, MAX
Example 4
MAX  VALUE1
Print
“The largest value is”, MAX
STOP Y N
START
Input
VALUE1,VALUE2
MAX  VALUE2 is
VALUE1>VALUE2

53. NESTED IFS One of the alternatives within an IF–THEN–ELSE statement
may involve further IF–THEN–ELSE statement

54. Example 6
Write an algorithm that reads three numbers and prints the value of the largest number.

55. Example 6
Step 1: Input N1, N2, N3 Step 2: if (N1>N2) then if (N1>N3) then MAX  N1 [N1>N2, N1>N3] else MAX  N3 [N3>N1>N2] endif if (N2>N3) then MAX  N2 [N2>N1, N2>N3] MAX  N3 [N3>N2>N1] Step 3: Print “The largest number is”, MAX

56. Example 6
Flowchart: Draw the flowchart of the above Algorithm.

57. Example 7 Write and algorithm and draw a flowchart to
read an employee name (NAME), overtime hours worked (OVERTIME), hours absent (ABSENT) and
determine the bonus payment (PAYMENT).

58. Example 7 Bonus Schedule OVERTIME – (2/3)*ABSENT Bonus Paid
>40 hours
>30 but  40 hours
>20 but  30 hours
>10 but  20 hours
 10 hours
£50
£40
£30
£20
£10

59. Step 1: Input NAME,OVERTIME,ABSENT
Step 2: if (OVERTIME–(2/3)*ABSENT > 40) then
PAYMENT  50
else if (OVERTIME–(2/3)*ABSENT > 30) then
PAYMENT  40
else if (OVERTIME–(2/3)*ABSENT > 20) then
PAYMENT  30
else if (OVERTIME–(2/3)*ABSENT > 10) then
PAYMENT 20
else
PAYMENT  10
endif
Step 3: Print “Bonus for”, NAME “is £”, PAYMENT

60. Your Flow Charts
Calculates greatest common factor (GCF) of two numbers.
A man has to get a fox, a chicken, and a sack of corn across a river. He has a rowboat, and it can only carry him and one other thing. If the fox and the chicken are left together, the fox will eat the chicken. If the chicken and the corn is left together, the chicken will eat the corn. How does the man do it? Solve the problem and make a flow chart with solution.
Change an engine oil algorithm.

61. Your Flow Charts
You want badly to take a friend out for a movie and dinner. And guess what? Your friend gladly accepted but you are broke. Now you have 36 hours (3 days) to get $100 and avoid embarrassment. Your sources are a last minute neighbor’s mow yard, parents, relatives, or else.
Watch The Big Bang Theory – The Friendship Algorithm online.
Have fun and enjoy summer.

62. tasks
Practice questions P20 q1-3