Beginners Computer Science – CS4HS (con’t)

1.44 Achievement Standard – continued on from Day 1

  • do not compare selection and insertion sort, better to do one of them and compare with quick sort
  • Quick sort – easy to do with hands and explain but hard to program. So good to do for 1.44 (scales that say heavy or lighter – just need binary, this or that)
  • worse case of quick sort is selection sort, at best will do lots better then selection sort
  • algorithms Cant TG


  • Hashing – algorithm that students do not need to know about. (Battleships).
  • Searching or sorting – one or the other, most common was sorting then searching, students who did either did quick well.
  • Easier to stick with one

1.44 Programming languages

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  • MS World is a complied program. Scratch is an interpreted program, have to have scratch.
  • Source code, object code – top of complied is source code

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  • real life is a mixture, Java is a mixture
  • programmes – if statements, iteration – real power of programme language – HTML not really a programme language
  • posters – put up in class, same program in different languages

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Level 2 – 2.44

Human Computer Interaction

  • students will use Heuristics – principles or guidelines
  • consistency is really good, e.g. ctrl+c = copy
  • provide useful feedback if someone makes an error – a heuristic is not a rule
  • come up in Level 3 for algorithms
  • heuristics are a ‘rule of thumb’
  • books – 2nd one better

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  • The Design of Everyday Things – Donald A Norman

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  • whole system needs to work not just the device or not just the interface
  • it is not the users fault if they can’t use the interface, it is badly designed

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  • interfaces to use with students
  • Heuristics (Nielsen)

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  • find something that takes more then a second to respond
  • feedback – reasonable time

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  • Lights on doors, green is safe, secure but for users of the door green would mean unlocked.

Data Representation

  • Activity – cards with dates, doubling up of dots – bits, binary counting

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  • Binary counter / binary piano – on/off
  • Code for letters (5 bits)
    • sound message – beeps high 1, low 0
    • insignificant number is to the right, number with less value – 1
    • CS Unplugged –
      • Steganography – a message hidden in a message
        “is the art and science of encoding hidden messages in such a way that no one, apart from the sender and intended recipient, suspects the existence of the message.” Wikipedia
    • message is that by adding one bit, twice as much power


  • making files smaller
  • most common is zipping files – zip file

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Jpeg CompressionEmbedded image permalink


  • RAID 5
  • first white, second black – even parity – error correctionEmbedded image permalink
  • bar code – number 9 is number that others add up toEmbedded image permalink
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  • Encryption: Caesar Cipher
  • why does this matter – how does this work in the really world, how many photos would fit in a camera, password, banking – want to be encrypted
  • encryption keys – how do the two people get the two keys
  • talk about application of coding
  • with encryption more processing is going on, some with if students do encryption by hand – they need to do more processing to decipher the code (or cipher the code)

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