Computational thinking: decomposition, abstraction and algorithms

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Computational thinking

Computational thinking is a way of solving problems so that a computer can help. Its main parts are decomposition, abstraction, pattern recognition and algorithmic thinking.
Decomposition: breaking a big problem into smaller, more manageable parts. Planning a school timetable can be split into rooms, teachers, classes and times.
Abstraction: removing unnecessary detail to focus on what matters. A map of the Tube shows stations and lines, not every street.
Pattern recognition: spotting similarities, so a solution can be reused.

Decomposition

Algorithms

An algorithm is a finite, ordered set of unambiguous steps for a task. It terminates for each valid input in the model used here, but different inputs may take different numbers of steps. Algorithms may process stored input and need not request new user input.
Algorithms can be shown in plain English, flowcharts or pseudocode.
Structure: sequence (steps in order), selection (decisions: IF), iteration (repeating: loops).

What is an algorithm?

Example

Algorithm to find the larger of two numbers: input A, input B; if A is greater than B then output A, otherwise output B.

Why it matters

Computational thinking helps design programs that are efficient and easy to test and change.

Control structures

Sequence follows instructions in order; selection chooses a branch; iteration repeats a body.
Example: input a mark, use IF to choose pass/fail, and repeat for each student.
Choose relevant details: omit button styling when designing scoring logic, but retain it when designing the interface.

Sequence in algorithms

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Practice questions

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1.What is an algorithm?
Easy
- Aa set of step-by-step instructions to solve a problem
- Ba type of computer
- Ca programming language
- Da hardware part
2.What is decomposition?
Easy
- Abreaking a problem into smaller parts
- Bhiding details
- Crepeating steps
- Dfixing errors
3.What is abstraction?
Easy
- Afocusing on important details and ignoring the rest
- Bbreaking into parts
- Crepeating
- Dtesting
4.What is pattern recognition?
Easy
- Aspotting similarities or trends
- Bremoving detail
- Clooping
- Ddeleting
5.Which structure repeats instructions?
Easy
- Aiteration
- Bselection
- Csequence
- Dinput
6.Which structure makes a decision?
Easy
- Aselection
- Biteration
- Csequence
- Doutput
7.Which is an example of abstraction?
Easy
- Aa Tube map showing stations but not streets
- Ba list of all streets
- Ca photograph
- Da full city plan
8.Which is an example of decomposition?
Easy
- Asplitting a game into graphics, sound, scoring and controls
- Bwriting one long program
- Cignoring parts
- Ddeleting code

More questions

9.What should a good algorithm be?
Easy
- Aclear, finite and unambiguous
- Bvague and endless
- Crandom
- Dsecret
10.Which three terms form the input-process-output model commonly used to describe a program?
Easy
- Ainput, process, output
- Bread, write, delete
- Cstart, stop, pause
- Dfirst, second, third
11.What does 'sequence' mean?
Easy
- Asteps carried out in order
- Brepeating steps
- Cdeciding
- Dending
12.Which is a result rather than a representation of algorithm steps?
Easy
- Aa reported forecast temperature of 18°C
- Ba flowchart
- Cpseudocode
- Dclear step-by-step natural-language instructions
13.An algorithm uses IF to compare two numbers and output the larger. Which control structure is being used?
Medium
- Aselection
- Biteration only
- Cno structure
- Drecursion only
14.Calculating the average of 100 test scores best uses:
Medium
- Aiteration
- Bno loop
- Cselection only
- Dno input
15.Why is decomposition useful in a team project?
Medium
- Adifferent people can work on different parts
- Bit makes all parts identical
- Cit removes testing
- Dit hides the problem
16.Which is an unambiguous instruction?
Medium
- AAdd 5 to the total
- BMake it better
- CDo something good
- DFix it somehow
17.Which is a limitation of abstraction?
Medium
- Aimportant details may be omitted
- Bit removes all detail
- Cit makes models complicated
- Dit creates bugs
18.What does 'finite' mean for an algorithm?
Medium
- Ait ends after a limited number of steps
- Bit never ends
- Cit is long
- Dit is hidden
19.Which task best shows pattern recognition?
Medium
- Anoticing that many programs need the same login check
- Btyping faster
- Cdrawing a map
- Dcounting characters
20.A taxi app only shows the pickup point and destination on a simple map. This is:
Medium
- Aabstraction
- Bdecomposition
- Citeration
- Da bug
21.Why might poor decomposition cause problems?
Medium
- Aparts may overlap or be missed, causing errors
- Bno problems occur
- Cprograms run faster
- Dtesting is easier
22.How does computational thinking help programmers?
Medium
- Ait makes problems easier to solve and programs easier to test
- Bit makes bugs
- Cit deletes code
- Dit removes data
23.What is a 'subproblem'?
Easy
- Aa smaller part of a larger problem
- Ban error
- Ca variable
- Da loop
24.What is an input?
Easy
- Adata given to a program
- Bdata produced
- Ca loop
- Dan error
25.What is an output?
Medium
- Adata produced by a program
- Bdata entered
- Ca variable
- Da loop
26.Which describes iteration in everyday life?
Medium
- Arepeating a recipe step until the dough is smooth
- Bmaking one decision
- Cdoing steps once
- Dstopping
27.An algorithm is a set of step-by-step instructions.
Easy
True or false?
28.Decomposition breaks a problem into smaller parts.
Easy
True or false?
29.Abstraction adds extra detail.
Easy
True or false?
30.Selection means making decisions.
Easy
True or false?
31.Algorithms can only be written in code.
Medium
True or false?
32.Which are parts of computational thinking?
Medium
- Adecomposition
- Babstraction
- Cpattern recognition
- Dalgorithmic thinking
- Ehardware repair
33.Which are program structures?
Medium
- Asequence
- Bselection
- Citeration
- Dinput
- Ecompression
34.Explain how decomposition and abstraction could be used to plan a quiz game.
Medium

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