Computational Thinking

• Analysis - Understanding the problem
• Design - Work out steps to solve said problem
• Implementation - Create a working program based on the design
• Testing - Making sure your solution fits all use cases
• Documentation - Describe how your solution works and how to use it
• Evaluation - Checking to see if your solution covers all points made in the original request

Waterfall Model

• Its simple to understand and use
• You move from one stage to the next stage
• This methodology is ideal for smaller projects

Analysis

User & Functional Requirements

• "I want a program that takes in a person's name and age, works out the year they were born and tells them"

  - Input(s): user name & age

  - Process(es): work out user birth year

  - Output(s): users birth year

• "A program is to be written to simulate the basic arithmetic functions of a calculator. The user should be asked to input two numbers and the sum (+), difference (-), product (*) and quotient (/) should be displayed"

  - Input(s): 2 numbers

  - Process(es): Calculate the sum, difference, product & quotient of the 2 numbers

  - Output(s): sum, difference, product & quotient of the 2 numbers

  Code

  numOne = int(input('Enter a Number: ''))
  numTwo = int(input('Enter Another Number: '))
  
  sumNum = numOne + numTwo
  diffNum = numOne - numTwo
  prodNum = numOne * numTwo
  quotNum = numOne / numTwo
  
  print('Sum: ' + str(sumNum))
  print('Difference: ' + str(diffNum))
  print('Product: ' + str(prodNum))
  print('Quotient: ' + str(quotNum))



• "A school needs a program to grade students' marks after an exam. The program should take in an integer between 0 and 100 and output a grade"

  - Input(s): an integer between 0 and 100

  - Process(es): Find the students grade

  - Output(s): The students grade

  Code

  gradeNum = int(input('Enter Number: '))
  while gradeNum < 0 or gradeNum > 100:
  	print('Error, number is <0 or >100')
  	gradeNum = int(input('Enter Number: '))
  
  if gradeNum >= 70: print('Student Achieved Grade A')
  elif gradeNum < 70 and gradeNum >= 60: 
  	print('Student Achieved Grade B')
  
  elif gradeNum < 60 and gradeNum >= 50: 
  	print('Student Achieved Grade C')
  
  elif gradeNum < 50 and gradeNum >= 40: 
  	print('Student Achieved Grade D')
  
  else: print('Student Failed')



• "A program is needed to calculate the speed at which an arrow is traveling at. It measures the time it takes the arrow to travel a marked distance between 2 sensors and calculates the speed of the arrow. The program should show the speed at which the arrow is traveling."

  - Input(s): the time it takes the arrow to travel between 2 sensors, distance between sensors

  - Process(es): How fast the arrow traveled

  - Output(s): Speed of the arrow

Design

Design Notation are ways of representing a program or algorithm. There are 2 types at this level

• Graphical Design Notation - Uses shapes to describe a design (Structure Diagrams & Flowcharts)
• Pseudocode - Uses Ordinary English to Define steps in a problem

Structure Diagrams

"I want a program that takes in 3 football scores, works out the total goals scored & the average, then outputs a message with the total & average"

Flowcharts

Pseudocode

INPUT "which is the best subject?"
WHILE answer != "computing science" THEN:
	SEND "Try Again" TO DISPLAY
SEND "Of Course It Is" TO DISPLAY

Wireframes

Practical Questions

• Using a graphical design notation of your choice, write algorithms for the following problems
• "Calculate the circumference of a circle giving the radius as input (2πr)"

  Pseudocode

  DECLARE pi INITIALLY 3.14
  SEND "Enter Radius: " TO SCREEN
  DECLARE radius INITIALLY KEYBOARD INPUT 
  DECLARE circumference INITIALLY 2*pi*radius
  SEND circumference TO SCREEN

  Code

  pi = 3.14
  radius = float(input('Enter Radius of Circle: '))
  circumference = 2*pi*radius
  print(circumference)

• "A quiz with 4 questions and a 2nd chance to get the correct answer after a hint is given"

  Pseudocode

  DECLARE questions INITIALLY ARRAY OF STRING ['5+5', '10-5', '5-3', '10-7']
  DECLARE hints INITIALLY ARRAY OF STRING ['15-5', '10-5', '1+1', '2+1']
  DECLARE answers INITIALLY ARRAY OF INTEGER [10, 5, 2, 3]
  
  FOR i IN RANGE(LENGTH questions) DO
  	SEND f"Question {i}: What is {questions[i]}" TO SCREEN
  	SET ans AS INTEGER KEYBOARD INPUT
  
  	IF ans != answers[i] THEN
  		SEND f"Wrong, hint: {hints[i]}" TO SCREEN
  		SET ans AS INTEGER KEYBOARD INPUT
  
  		IF ans != answers[i] THEN
  			SEND f"Wrong, try another question" TO SCREEN

  Code

  questions = ['5+5', '10-5', '5-3', '10-7']
  answers = [10, 5, 2, 3]
  hints = ['15-5', '10-5', '1+1', '2+1']
  
  for i in range(len(questions)):
  	ans = int(input(f'Question {i}: What\'s {questions[i]}: '))
  
  	if ans != answers[i]:
  		ans = int(input(f'Wrong, hint: {answers[i]} is the same as {hints[i]}'))
  		if ans != answers[i]: print('Wrong, try another question')

• Investigate online tools for creating design notations. For Example
• Create programs to solve each of the problems above, using a programming language of your choice

Implementation

• Character - A symbol, letter or number, e.g 'J'
• String - A list of characters, e.g 'Hello'
• Integer - A whole number, e.g 3
• Float/Real Number - A decimal number, e.g 3.14
• Boolean - Either True or False

Data Structures

Computational Constructs

• Arithmetic Operations - A process that is carried out on an item of data, e.g +,-,/,*. age += 1, ageDiff = ageOne - ageTwo etc
• String Concatenation - The joining of 2 strings into 1, e.g firstName = 'Ewan', secondName = 'Travers', name = firstName + ' ' + lastName

• Equals - =
• Compared To - ==
• Greater Than - >
• Less Than - <
• Greater Than or Equal To - =>
• Less Than or Equal To - <=
• Not Equal To - !=

• AND - Both conditions must be true for the output to be true
• OR - Only one condition must be true for the output to be true
• NOT - Condition must be false for the output to be true

• Simple Conditional Statement - if age > 18: # do something
• Complex Conditional Statement - if age < 18 and age < 35: # do something

Questions

• What does assignment do
• Write assignment statements for your name and age using a programming language of your choice
• Name 2 operations used in programming languages
• Which type of operations produce an answer of true or false
• What is concatenation
• State 2 relational operators
• Which type of operation uses NOT

Control Structures

• Fixed Loop - Loop code a predetermined number of times, e.g for i in range(4): # Do something
• Conditional Loop - Only loops as long as the condition is true, e.g while pWord != 'password': # do something

Predefined Functions

• Function - Code that has already been written & performs an action, returning a value
• Procedure - Code that has already been written and performs an action, not returning a value

• len (length) - Returns the number of characters in a string or items in an array
• round - Rounds a number to a specific number of decimal places
• random - Chooses a random element from a list
• range - chooses a random element within a specified range

Standard Algorithms

• Input Validation - Making sure the Input given is acceptable

  grade = int(input('Enter Percentage: '))
  while grade < 0 or grade > 100: 
  	grade = int(input('Error - Enter Percentage: '))

• Running Total within a loop - How far the loop has gone through

  total = 0
  points = [1,2,3,4,5,6]
  
  for i in range(len(points)):
  	total += points[i]
  
  print(total)

• Traversing a 1D Array - Running through all values in an array

  array = ["one", "two", "three", "four"]
  for i in range(len(array)):
  	print(giant[i])

Questions

• Name 2 types of subprogram

  Function & Procedure
• What is the difference between a procedure & a function

  A procedure does not return a value & a function does return a value
• What is a predefined function

  A piece of code that can be ran and given information, returning a value as output
• What is a parameter

  Information required by a subprogram to operate

Testing

Test Cases

• Normal - Data that you would expect to work or be acceptable an that lies within the range, e.g 2, 45
• Extreme - Data at the lower and upper limits of the range, e.g 0, 50
• Exceptional - Data that should not be accepted by the program, e.g -7, 'String'

Error Types

• Syntax Error - Occurs when the rules of the programming language are broken, e.g prints(len(name)) # instead of print(len(name))
• Execution Error - Occurs whilst the program is running, e.g res = 5/0
• Logic Error - Occurs when mistakes are made in the design of the program, the program will run but won't give the expected output

Test Tables

Test Table - Accepting input of a score between 1 and 99 inclusive

Documentation

Guides

• User Guide - How the user can use the software effectively
• Technical Guide - Requirements for the system, either hardware or software

Evaluation

How to Evaluate Work

• Fitness for Purpose - Does the program perform as specified in the software specification
• Code Efficiency - Has made use of the correct control structures and computational constructs
• Robustness - How well the program deals with unexpected inputs, usually determined at the testing stage
• Readability - How easily the code is to read and understand, readability should include:
• Internal Commentary (Comments)
• Meaningful Variable Names
• Indentation/White Space (Spaces or Tabs between code lines)

What is HTML

Page Structure

<!DOCTYPE html>
<html>
	<head>
		<title>Webpage Title goes Here</title>
	</head>

	<body>
		<!-- Displayed Content Goes Here -->
	</body>
</html>

• <!DOCTYPE html> and <html> - This tag tells the web browser what language you're using to structure the page. This must always be at the top of the page
• <head> - This tag encompasses tags like the title, css, scripts & meta tags
• <title> - This tag will be the webpages title that shows up in the window tab of the browser
• <body> - This tag encompasses all viewable content on the webpage

• All tags have to be surrounded like this: <tagname>
• All tags have to be opened and closed, the end tag is always shown with a />
• All tags can be referred to as elements

CSS Rules

• Selector - This declares which HTML elements are to be styled, this can be an element, class or ID
• Property - This is the CSS property that is going to be edited, e.g text color
• Value - This is the value you assign to the corresponding CSS property
• A declaration requires a valid property value pair, a rule may contain multiple of these declarations

• h1 - This is the selector
• color - This is the property
• blue - This is the value
• color: blue; - This is a declaration

• Text: font (font-family, font-size)
• Color & Background Color
• Alignment (left, right, centre or justified)

Binary

Counting in Base 10

Counting in Base 2

Floating Point Representation

• 314 is referred to as the mantissa
• 25 is referred to as the exponent
• and the x10 is referred to as the base

ASCII

Bitmapped Graphics

• 1: 2 colors
• 2: 4 colors
• 8: 256 colors
• 16: 65535 colors
• 24 (true color): 16777216 colors

Vector Graphics

• No pixelation, independent of zoom
• Shapes can be layered on top of each other

• Fill Color
• Line Color
• Coordinates (position)

Basic Computer Architecture

RAM

• Programs loaded from the Hard drive into RAM
• RAM is faster to access than the Hard drive
• Data is lost when the PC is turned off or loses power

Processor

• The data being processed
• The instructions being run
• Memory addresses that need to be accessed

Fetch-Execute Cycle

1. Processor sets up address bus with required address
2. Processor activates the read line
3. Instruction transferred from memory to processor by using the data bus (fetch)
4. Instructions decoded then executed

Translation

• Compiler - Compiles & runs all the code at once
• The code runs very fast
• Machine code isn't easily edited once compiled
• Interpreter - Compiles & runs code one line at a time
• Can be used to easily find bugs
• The program runs slowly

Firewalls & Encryption