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Tracing algorithms

I can use trace tables to test the logic of an algorithm.

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New

Tracing algorithms

I can use trace tables to test the logic of an algorithm.

Lesson details

Key learning points

  1. Trace tables can be used to walkthrough and understand the logic of an algorithm.
  2. Trace tables can be used to help find logical errors in algorithms.

Keywords

  • Trace table - a tool used to track the values of variables and the flow of execution in an algorithm or program, step by step

  • Error - a mistake or unexpected behaviour in a program that prevents it from working correctly

  • Modulo - an operation that gives you the remainder when one number is divided by another

Common misconception

Using trace tables guarantees correct logic and code.

Trace tables can be subject to human error and can be impractical to use for complex algorithms.

Initially, pupils can struggle to keep track of variable changes in trace tables. Model the completion of trace tables slowly by narrating the changes as they happen.
Teacher tip

Equipment

Licence

This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Prior knowledge starter quiz

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6 Questions

Q1.
What is a set of step-by-step instructions to solve a problem called?

Correct Answer: algorithm, an algorithm, algorithms

Q2.
Why is it helpful to develop an algorithm’s logic before coding?

Correct answer: It makes problem solving easier.
It wastes time.
It creates unnecessary steps.
It’s only useful for flowcharts.

Q3.
What is a diagram that represents logic or data (or similar alternatives)?

Correct Answer: flowchart, flow chart

Q4.
What does decomposition involve?

ignoring the problem entirely
Correct answer: breaking down problems into smaller subproblems
writing a program directly
creating a flowchart

Q5.
What is abstraction in computational thinking?

focusing on irrelevant details
writing a program in plain language
ignoring the important parts of a problem
Correct answer: focusing on the important parts and ignoring irrelevant details

Q6.
What is a way to express an algorithm in plain language (or similar alternatives)?

Correct Answer: pseudocode, pseudo code

Assessment exit quiz

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6 Questions

Q1.
Match the terms with their definitions.

Correct Answer:trace table,a tool to track variable values and execution flow

a tool to track variable values and execution flow

Correct Answer:error,a mistake in a program that prevents it from working correctly

a mistake in a program that prevents it from working correctly

Correct Answer:modulo,an operation that gives the remainder when dividing two numbers

an operation that gives the remainder when dividing two numbers

Correct Answer:human error,mistakes made by people when creating trace tables

mistakes made by people when creating trace tables

Correct Answer:execution,the process of running an algorithm or program

the process of running an algorithm or program

Q2.
What is a trace table used for?

to draw flowcharts
to write pseudocode
Correct answer: to track variable values in a program
to translate algorithms into code

Q3.
What is a common limitation of trace tables?

they are always correct
Correct answer: they can be subject to human error
they only work for pseudocode
they cannot track variable values

Q4.
What is the result of 10%3?

Correct Answer: 1, one

Q5.
Arrange these steps into the correct order for creating a trace table.

1 - Write the algorithm.
2 - Identify the variables in the algorithm.
3 - Track the values of variables step by step.
4 - Analyse the results to find errors.

Q6.
Why might trace tables be impractical for complex algorithms?

they are too simple to use
they cannot track variables
they only work for pseudocode
Correct answer: they can become too large and difficult to manage

Lesson appears in

UnitComputing / Algorithms

AQAComputing

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OCRComputing

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