Computational thinking skills

Computer Science AS · Algorithm design and problem-solving. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

Computational thinking is a way of approaching a problem so that a computer can help to solve it. Two of its skills are abstraction and decomposition.

Abstraction means keeping only the details that are needed to solve the problem and leaving out the rest. The result is an abstract model: a simpler version of the real system. A map is a good example. It shows roads and towns but not every tree.

Decomposition means breaking a problem into smaller sub-problems, and breaking those down again, until each one is easy to solve. Each small part can then be written as a program module, which is a procedure or a function.

Rules to remember

Abstraction: filter out unnecessary detail and keep the essential features.
Benefits of abstraction: the problem is simpler to understand, the program is shorter and quicker to write, and it needs less memory and processing.
To build an abstract model, ask of each detail: does the solution need it? If not, leave it out.
Decomposition: split a problem into sub-problems until each can be coded directly.
Benefits of decomposition: modules can be written and tested separately, shared between programmers and reused.
A function returns a value; a procedure carries out a task and does not return a value.

Common mistake

Students swap the two terms. Abstraction removes detail; decomposition splits the problem into parts. Neither one is the same as writing the code.

Worked example

A program will calculate the cost of delivering a parcel. The cost depends on the weight of the parcel and the distance travelled. Which of these belong in the abstract model: weight, colour of the box, distance, name of the driver?

The purpose of the model is to calculate a delivery cost.
Weight and distance are used in the calculation, so they are essential details.
The colour of the box and the name of the driver do not change the cost, so abstraction removes them.

Answer: Keep weight and distance; leave out the colour of the box and the name of the driver.

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