Using Trace Tables

A trace table is a technique used to track the values of variables as an algorithm executes, step by step. Trace tables are an essential tool for testing, debugging, and understanding how an algorithm works.

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Why Use Trace Tables?

Trace tables help you:

• Understand how an algorithm works by following it through step by step
• Find errors (bugs) in an algorithm by checking whether the output is correct
• Predict the output of an algorithm for a given input
• Verify correctness — check that an algorithm produces the expected results

They are frequently tested in GCSE exams. You will often be given pseudocode or a flowchart and asked to complete a trace table.

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How to Create a Trace Table

1. Create columns — one for each variable in the algorithm, plus one for any output.
2. Work through the algorithm line by line.
3. Update the table whenever a variable changes value.
4. Record output in the output column whenever a PRINT or OUTPUT statement is reached.

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Example 1: Simple Loop