Paper 2 revision

• Computational Thinking


  The steps you take to find the best solution to a complex problem
• Three Key Techniques for Computational Thinking

  • DECOMPOSITION - breaking a complex problem down into smaller problems and solving each one individually
  • ABSTRACTION - picking out the important bits of information from the problem, ignoring the specific details that don't matter
  • ALGORITHMIC THINKING - a logical way of getting from the problem to the solution
• If the steps you take to solve a problem follow an algorithm then they can be reused and adapted to solve similar problems in the future
• Computational thinking in real-life

  • Deciding which film to watch at the cinema with your family
• Decomposition


  Breaking down a complex problem into smaller problems and solving each one individually
• Abstraction


  Picking out the important bits of information from the problem, ignoring the specific details that don't matter
• Algorithmic thinking

  A logical way of getting from the problem to the solution
• Computer scientists rely on decomposition, abstraction and algorithmic thinking to help them turn a complex problem into small problems that a computer can help them to solve
• Decomposition and abstraction are important skills that you'll need to develop if you want to succeed in your exams
• Pseudocode


  Not an actual programming language but it should follow a similar structure and read like one (roughly)
• Pseudocode is quick to write and can be easily converted into any programming language
• There are different ways to write pseudocode - they are all equally correct as long as the person reading the code can follow it and understand what you mean
• Pseudocode should be more 'wordy' than a formal programming language, but easier to understand
• Even though pseudocode isn't a formal programming language you still need to make sure it's readable, easy to interpret and not too vague
• Pseudocode is a great way to write an algorithm in the exam if you're not told how to give your answer
• Flowchart

  A way to show an algorithm using different shapes to represent different commands
• Different shapes used in flowcharts

  • Decision (diamond)
  • Start/Stop (rounded corners)
  • Inputs/Outputs (parallelogram)
  • Sub Programs (reference other flowcharts)
  • Processes (rectangle)
• Flowcharts for different algorithms

  • Calculating salary after 10% increase
  • Checking password validity
  • Linear search
• Flowcharts should show the general flow of an algorithm without going into too much detail at each step
• Everything covered in the programming section will work slightly differently in different programming languages, but the principles are the same
• Five main data types in programming languages

  • Integer
  • Real (or float)
  • Boolean
  • Character
  • String
• Integer

  Whole numbers only
• Real (or float)


  Numbers that have a decimal part
• Boolean


  Can only take one of two values, usually TRUE or FALSE
• Character


  A single letter, number, symbol
• String


  Used to represent text, it is a collection of characters
• Each data type is allocated a different amount of memory
• Using the correct data types makes code more memory efficient, robust (hard to break) and predictable
• Weakly typed language

  Will try to convert data types to avoid errors, however this can lead to unpredictable results
• Strongly typed language

  Won't try to convert data types and so will produce more errors but more predictable results
• Casting


  Using functions to manually convert between data types
• The integer 1, the real 1.0 and the strings "1" and "1.0" are all different
• Basic arithmetic operators

  • Addition (+)
  • Subtraction (-)
  • Multiplication (*)
  • Division (/)
  • Exponentiation (^, **)
  • Quotient (DIV)
  • Remainder (MOD, %)
• Dividing integers might behave oddly in some programming languages, e.g. 5/2 may give the answer 2 instead of 2.5</b>
• Operators


  Special characters that perform certain functions
• Basic Arithmetic Operators

  • Addition +
  • Subtraction -
  • Multiplication *
  • Division /
  • Exponentiation ^ or **
  • Quotient DIV
  • Remainder (modulus) MOD or %
• Arithmetic operators

  • Take two values and perform a maths function on them
  • Addition, subtraction, multiplication and division operators do what you'd expect
  • The exponentiation operator is used to raise a number to a power
  • The DIV operator returns the whole number part of a division and the MOD operator gives the remainder
• Dividing integers might behave oddly in some programming languages, e.g. 5/2 may give the answer 2 instead of 2.5
• Computers follow the rule of BODMAS (Brackets, Other, Division, Multiplication, Addition & Subtraction)
• Assignment operator


  Used to assign values to constants or variables