2.1 - Elements of computational thinking

Question 1

What is abstraction

Answer 1

Where a programmer hides all but the relevant data about an object in order to reduce complexity and increase efficiency. It gets rid of unnecessary detail.

Question 2

What will a computer scientist do when planning a system to “plan ahead”?

Answer 2

1) Determine outputs required
2) Determine the inputs necessary to achieve the outputs
3) Consider the resources needed
4) Consider user expectations

Anyone else can:
1) Decide what is to be achieved
2) Determine prerequisites
3) Determine what is possible

Question 3

What is an example of thinking ahead in computers?

Answer 3

Caching
1) Data that is used is stored in the cache/RAM in case it is needed again.
2) Allows faster access for future use

Question 4

What is decomposition?

Answer 4

Any large problem is divided into smaller sub-problems.

Eventually, they will equate to program modules or groups of modules.

Order of execution needs to be taken into account – may need data to be processed by one module before another can use it.

Some modules need to be accessible in an unpredictable way.

Large human projects benefit from the same approach.

Question 5

What is concurrent thinking?

Answer 5

Concurrent thinking is the process of completing more than one task at any given time.

This doesn’t always mean that you have to be working on multiple tasks at once, however.

Concurrent processing is when tasks are given slices of processor time, to give the illusion that tasks are being performed simultaneously, and concurrent thinking is similar to this. It allows you to spot patterns and parts of problems where concurrency can be applied, thus speeding up processes.

Question 6

What is the difference between concurrent processing and parallel processing?

Answer 6

Parallel processing is when multiple processors are used to complete more than one task simultaneously.

Meanwhile, concurrent processing is when each task is given a slice of processor time to make it look like the tasks are being completed simultaneously when in reality they are executed sequentially.

Question 7

What are the benefits and drawbacks of concurrent processing?

Answer 7

Benefits of concurrent processing
● The number of tasks completed in a given time is increased.
● Less time is wasted waiting for an input or user interaction, as other tasks can be completed.

Drawbacks of concurrent processing
● Concurrent processing can take longer to complete when large numbers of users or tasks are involved as processes cannot be completed at once.
● There is an overhead in coordinating and switching between processes, which reduces program throughput.
● Just as with parallel processing, not all tasks are suited to being broken up and performed concurrently

Question 8

What is representational abstraction?

Answer 8

A technique in which excessive details are removed to arrive at a representation of a problem that consists of only the key features.

Question 9

Which form of abstraction involves grouping together similarities within a problem to identify what kind of problem it is?

Answer 9

Abstraction by generalisation

Question 10

What is meant by data abstraction?

Answer 10

A form of abstraction in which details about how data is being stored are hidden.

Question 11

What kind of problems make use of multiple levels of abstraction?

Answer 11

Large, complex problems

Question 12

State two advantages of using abstraction in software development

Answer 12

• Easier for programmers to focus on core elements
• Reduces the time needed to be spent on the project.
• Prevents program from getting unnecessarily large.

Question 13

Give two applications of layers of abstraction

Answer 13

-Networking (TCP/IP layer)
- Programming languages

Question 14

State two advantages of using abstraction in programming languages

Answer 14

1. hiding information that is too complex or irrelevant
2. more efficient software design
3. reduces the time spent on the project and prevents
   the program from getting unnecessarily large

Question 15

What three considerations do programmers need to make regarding inputs and outputs when thinking ahead?

Answer 15

• Method of input/output (device used)
• Data structures used
• Data types used
• Order of data

Question 16

What are preconditions?

Answer 16

Requirements which must be met before a program can be executed.

Question 17

Where can preconditions be defined?

Answer 17

Within the code or within documentation.

Question 18

Give an example where preconditions are required.

Answer 18

Stack functions
- Check that a stack is not empty when popping an element from a stack
- Check that a stack is not full when pushing an element onto a stack

Question 19

State two advantages of including preconditions within the documentation accompanying a subroutine.

Answer 19

Reduces the length of the program
- Reduces the complexity of the program
- Saves time needed to debug and maintain a longer program
- Makes subroutine more reusable

Question 20

What is the name given to the technique in which algorithms are used to predict which instructions are likely to soon be used?

Answer 20

Prefetching

Question 21

Give two examples of reusable program components.

Answer 21

• Abstract data structures eg. queues and stacks
• Classes
• Subroutines

Question 22

What is the first stage of thinking procedurally

Answer 22

Taking the problem defined by the user and breaking it down into its constituent parts.

Question 23

What is the purpose of problem decomposition?

Answer 23

To make complex problems easier to solve and more manageable by allowing tasks to be divided between a group of people according to individual skill sets.

Question 24

State another name given to top-down design.

Answer 24

Stepwise refinement

Question 25

What is the purpose of top-down design?

Answer 25

Continually break problems down into subproblems until each subproblem can be represented as a single task and ideally a self-contained subroutine.

Question 26

What are the benefits of using top-down design?

Answer 26

● Problems can be solved and modules - developed by different people.
● Tasks can be tested separately - modules are self-contained

Question 27

What sort of problems is top-down design suited to?

Answer 27

Large, complex problems

Question 28

What is the second stage of thinking procedurally in software development?

Answer 28

Identifying components of a solution

Question 29

What must a software developer do before designing a subroutine to solve a particular problem?

Answer 29

1. If its possible to make
2. if it has already been made

Question 30

What do software developers need to consider when recombining components of a solution?

Answer 30

The order in which subroutines are executed, and how they interact with each other, based on their role in solving the problem.

Question 31

What is a decision?

Answer 31

A decision is a result reached after consideration

Question 32

When are decisions made?

Answer 32

A decision is made whenever you have to choice to make.

Question 33

What is the shape used to indicate a decision in a flow chart?

Answer 33

A diamond

Question 34

How do you make effective decisions?

Answer 34

By evaluating the importance of different factors and selecting options which satisfy the needs of the task the most appropriately.

Question 35

What is the procedural interface ?

Answer 35

You don’t need to know the ins and outs of a procedure, just the name etc