Topic 1 - Computational Thinking

Decomposition

• Analysing a complex problem

• Breaking it down

• Makes it more manageable

  • Without it is very hard to solve

Examples of decomposition

• A crime

  • What crime

  • When it was committed

  • Where it was

  • What evidence

  • If any witnesses

Abstraction

• Process of filtering out unnecessary characteristics of the problem

• Can get a general idea of what the problem is

Example of abstraction

• Finding volume of a rectangle

  • Only need height, width and length

  • Do not need hypothenuse or area

Benefits of subprograms

• Small in size so easier to write

• Easier for others to understand

• Less program as repeated parts don’t have to get written out 10 times

Logical operators

• AND

• OR

• NOT

Relational operators

• <=

• ==

• >=

Syntax Error

• Breaks the rules of grammar of the language

• Spelling errors, indentation

Logic Error

• Caused by incorrect or unwanted behaviours

• Mixing up variable names, wrong arithmetic operator

Run time error

• Cannot execute the instructions of the code

• Causes crash

• Index out of range, divide by zero

Standard algorithms

• Linear search

• Binary search

• Bubble sort

• Merge sort

Linear search

• Find length of data set

• Set counter to 0

• Examine value held in list at counter value

• Match?

  • Yes

    • Return message and end search

  • No

    • Increment counter

    • Repeat

Binary search

• Set counter to middle position of list

• If value a match, search ended

• If less, divided in half and upper ignored

  • Vice versa

• Search moves to midpoint of remaining items

• Continue this until found

Bubble sort

• Start at beginning of list

• Compare first with second

• If 1 bigger than 2

  • Swap

• Compare THIS value with next

• Repeat

• Takes longer because more comparisons than merge sort

Merge sort

• More complex

• Uses divide and conquer

• Takes unsorted list

• Splits in half

  • Repeats until all elements are separated

• Compares in pairs

• When first member of pair has been sorted, its time for the second one

Pseudocode

• Not a programming language

  • Simple way of writing code

Benefits of Pseudocode

• Quickly convertible

• Easy to understand

• Does not matter if there are errors in syntax

Drawbacks of Pseudocode

• Time consuming to produce

• Hard to see how it flows

Benefits of Flowcharts

• Easy to see how program works

• International standard

Drawbacks of Flowcharts

• Changes mean whole thing has to be re-done

• Can become huge

Selection

• Making a decision

• Decides what will come next

• If, elif

Iteration

Repeating a certain step until told otherwise

Count controlled vs condition controlled iteration

• Count controlled

  • If count > 0:

  • For x in range:

  • Repeats until no longer validated

• Condition controlled

  • While

Modulus

Finds remainder

Variables rules

• Contains ONLY numbers and letters

• At least one letter

• Can be changed throughout running of code

• Must be meaningful

Global Variables

• Can be accessed throughout program

• Has to have different name to local variable

Local Variables

Confined to subprogram

Constant

• Cannot be changed while running

• In uppercase

Types of data storage

• Arrays

• Records

• Strings

Arrays

Stores data of same data type

Record

Stores data of different data types

String

Represents a sequence of letters

Test data types

• Normal data

• Boundary data

• Erroneous data

Normal data

• Sensible valid data

• Can be processed

Boundary Data

Falls at boundary of any ranges

Erroneous data

Invalid input that won’t be accepted

Test plan

• In a table containing

  • Test number

  • What should happen

  • What does happen

  • Type of test

Types of Debugging

• Single step

• Set break points

• Watchers

Single step

Can step through lines of code one at a time

Set break points

When code stops at certain point

Watchers

Looks out for certain variables

Truth tables: AND

if any 0s = 0

Truth tables: OR

if any 1s: 1s

Order of procedures

Brackets

Not

And

Or

Brad Never Ate Oregano