Computational Thinking, Problem-Solving and Programming
Topic 4
Assessment Objectives
Assessment objective 1: classify, define, draw, label, list, state
Assessment objective 2: annotate, apply, calculate, describe, design, distinguish, estimate, identify, outline, present, trace
Assessment objective 3: analyse, comment, compare, compare and contrast, construct, contrast, deduce, demonstrate, derive, determine, discuss, evaluate, examine, explain, formulate, interpret, investigate, justify, predict, sketch, suggest, to what extent
Computational Thinking
Five different types of computational thinking
Find out what they are Examples of each
Example
You have decided to invite your friends over to watch the big basketball game. You are going to make food for everyone.
How will you use computational thinking to make sure your day goes well?
Give examples of where you can apply each of the five types of computational thinking to this situation.
Thinking Ahead
Think back to the basketball game task
In what ways did you need to think ahead?
What examples of thinking ahead do you know of from the world of computing?
Pre-conditions and post-conditions A method of specifying what a
procedure accomplishes without going into the details of how it works
Go and write me a function. I don't care how you do it, just make sure these
requirements are met.
Example
void print_sqrt(double d) {// pre-condition: d>=0// post-condtion: sqrt(d) written // to standard output
}You should add these comments to every non-trivial method that you write in your Java IA
Working in teamsYour job is to write
the function. When I call it, I will ensure
that the pre-conditions are met.
Well as long as you meet the pre-conditions, I
guarantee it will work.
But just to be on the safe
side my function will check if a
pre-condition has been
violated, and report an
error if it has.
Conditions to Decisions
IB documentation wants you to realise that pre- and post-conditions affect the decisions that will be made in the implementation of the function
Think back to the sqrt() function Give an example of an if… then…
block that will follow from the preconditions
Your turn
Consider a function that tells you how many times a particular letter occurs within a word
What pre- and post-conditions will there be?
Write the function in Java, and link the decisions in the function to the conditions outside it
Gantt chartsDecomposition in subtasks. Thinking procedurally, thinking ahead, thinking concurrently.
Review
What are the five types of computational thinking?
Concurrent thinking in everyday life
Things to do: Put the clothes into the washing
machine and turn it on Take the clothes out of the washing
machine and hang them up Put the food into the oven Take the food out of the oven
What order is best?
Thinking concurrently
What examples of concurrent thinking can you think of from the world of computer science?
Multi-tasking OS time-slicing scheduling interrupts
RDBMS (database) transactions
Dining Philosophers
Philosophers like to think a bit, eat a bit, think a bit, etc.
Need two chopsticks to eat
Have to pick them up one at a time
Can't steal them from someone else! DEA
DLOCK
Thinking Abstractly
a publication a newspaper
The San Francisco Chronicle the May 18 edition of the The San Francisco
Chronicle my copy of the May 18 edition of the The San
Francisco Chronicle my copy of the May 18 edition of the The San
Francisco Chronicle as it was when I first picked it up (as contrasted with my copy as it was a few days later: in my fireplace, burning)
Abstraction
Considering the same object from different viewpoints
Different aspects of the object are important to different audiences
Describe a car from the viewpoint of: A driver A mechanic A physicist
What are the benefits of abstraction? How does it help us?
The best example of abstraction in the world ever
Some abstractions
TCP Segment
IP Datagram
Ethernet Frame
HTTP Packet
Different names for different types of packet
Task: The OSI Model and abstraction Write a brief outline of how the OSI Model
uses abstraction. How does it make complex tasks simple?
What does each layer know about the one below? What does each packet know about its payload?
Imagine you are Mr Brown and you want to send a letter to the head of ISKL. What layers of abstraction exist to facilitate this process? Describe them and explain why they are useful.
Flowcharts
yes
noyes
no
I = 0
I = N?
START
ARRAY[I]=TARGET?
I = I + 1
STOP
STOP
This algorithm finds the index of TARGET within an ARRAY of N elements.
Check that you understand how the algorithm works by explaining how you could tell whether or not TARGET was found.
Tasks
Flowchart for finding a given value in an array
Flowchart for BubbleSort Trace tables
Read chapter from the blog Do exercises
Task: Produce a trace table
int a = 2, b = 4, c;int x = 20, y = 20;for (int i = 0; i < 3; i ++) { System.out.print(" i = " + i); for ( int j = 0; j < 3; j ++) { c = a * b; System.out.print(" c = " + c); a ++; b ++; x += 20; } // end inner loopx = 20;y += 20;} // end outer loop
yes
no
B – N < 1?
START
B = B - N STOP
OUTPUT A, BA = A + 1
A = 0
Trace this flowchart for B = 26, N = 7
State what the algorithm does and note preconditions and postconditions
Write the algorithm in pseudocode
Write the algorithm as a method in Java. (B and N should be passed into the method as parameters. A and B should be returned by the method.)
INPUT B, N
Do this exercise quietly, on your own. Don'tshout out the answers. Let other people work.
Practice on these
An algorithm that takes an integer input N and prints the Fibonacci
sequence up to N
An algorithm that takes an integer input N and prints the sum of all numbers from one up to
N
An algorithm that takes an integer input N and prints out all the integer factors of N
An algorithm that takes an integer input N and
prints out the Nth triangular number
An algorithm that takes an integer array input A[] and prints out the largest number in A[]
An algorithm that takes an integer array input A[] and prints out true if it is palindromic and false otherwise
An algorithm that takes a 2d integer array argument A[][] and
outputs the sum of each column
An algorithm takes takes an integer N and a sorted array A[] and inserts N in the right
place in A
An algorithm that takes an integer array input A[] and output true if it is sorted (ascending or descending)
and false otherwise
An algorithm that takes an integer argument N and outputs its position in
linked list LIST, or -1 if it is not found
An algorithm that takes integer arguments N and B and prints N out in base B (assuming that N is denary
to start with)
An algorithm that takes string input A and B and outputs true if A is a substring of B and
false if not
Do this exercise quietly, on your own. Don'tshout out the answers. Let other people work.