Computational Thinking Activities The Magic of Computer Science Aram, Job, Grant The Magic of Computer Science Materials from CS4FN. The Magic of Computer Science. Card Tricks Special . Peter McOwan and Paul Curzon. Queen Mary University of London. www.cs4fn.org.

The 21 Card Trick Card trick activity demonstrates Algorithmic thinking. “The point about an algorithm is that if you follow its instructions exactly, you are guaranteed to achieve what you are trying to do...if the algorithm is correct” - CS4FN CS4FN also link this activity to testing : “How could we make sure our algorithm is correct and our trick does work? Well we could do the trick lots of times and check it works every time” – CS4FN

Activity 1. 21 Card Trick – With Cards KS3 Steps: Show the class the trick. With the algorithm teach a group of pupils the trick. This initial group of pupils then show their own groups the trick. They then supervise the groups learning the algorithm. Learning Objective : Understand that by following an algorithm, exactly, the outcome is guaranteed and that not following an algorithm correctly will lead to an error.

The high level algorithm Deal 21 cards in 3 columns of 7 Ask the audience member to pick a card but do not tell the magician Ask the audience member to identify the columns containing the card Place the chosen column of cards between the other two Repeat the process for 4 deals The chosen card is now in the middle of the middle column

Problems and Misconceptions. It is expected that the pupils will make mistakes when following the algorithm. This will emphasise the importance of precision. Scaffolding and a range of learners. Use fewer cards i.e. columns of 5. Mixed ability groups. Support and help during exercise. Pre Requisite Skill and Knowledge. ? Resources. Cards and Algorithm. Links to curriculum and computational thinking progression (CAS) Understands that computers need precise instructions.(AL) Detects and corrects errors i.e. debugging, in algorithms.(AL)

Activity 2. 21 Card Trick – With Python More able KS3 / KS4 Steps: Remind class/ introduce the class to the trick. Provide High level algorithm from task 1 Decompose this into more detailed algorithm Use more detailed algorithm to program algorithm (Python) Learning Objectives : Further understand that by following an algorithm, exactly, the outcome is guaranteed and that not following an algorithm correctly will lead to an error. Understand that splitting an algorithm into smaller parts make it easier to understand (and convert into code) – Decomposition.

Problems and Misconceptions. Again it is expected that the pupils will make mistakes when programming the algorithm emphasising the importance of precision and introducing / emphasising debugging. Scaffolding and a range of learners. Partially completed code. Support and help during exercise. Pre Requisite Skill and Knowledge. Python (Lists, Loops, Input/Output, Variables) Resources. PCs, Python Environment, Links to curriculum and computational thinking progression (CAS) Understands that computers need precise instructions.(AL) Detects and corrects errors i.e. debugging, in algorithms.(AL) Understands that algorithms are implemented on digital devices as programs. (AL) Designs simple algorithms using loops, and selection i.e. if statements.(AL)