AQA · GCSE · Computer Science
Course version: 8525 · Version from Sept 2020
Determine the purpose of simple algorithms. Students should be able to use…
Full specification wording
Representing algorithms: Determine the purpose of simple algorithms. Students should be able to use trace tables and visual inspection to determine how simple algorithms work and what their purpose is.
A simple algorithm is a finite sequence of unambiguous steps that transforms inputs into outputs.
Checked against the AQA 8525 specification (opens in a new tab) on .
- Point 8 of 8
Study notes
From the checked teaching notes for this specification point.
The idea
A simple algorithm is a finite sequence of unambiguous steps that transforms inputs into outputs. To determine its purpose, read the steps and ask what changes between the start and the end: which values are read, which are calculated, which are compared and which are output. Visual inspection means following the flow of sequence, selection and iteration by eye to see the overall effect. A trace table makes this rigorous: create a column for each variable and one row per step, record each value as it changes, and note any output produced. The completed table shows the pattern of values, so you can state the purpose in one sentence, for example 'it finds the largest of three input numbers' or 'it counts how many inputs are positive'.
What earns the marks
- Identifies the inputs the algorithm reads and the outputs it produces.
- Follows sequence, selection and iteration correctly to describe the overall effect.
- Uses a trace table with a column per variable and a row per step to record changing values.
- States the purpose as a short general description rather than restating individual lines of code.
- Recognises the pattern in traced values, such as finding a maximum, counting items or totalling values.
Common mistakes and how to put them right
Describing each line in turn instead of summarising the overall purpose.
Put it right: State one general aim the whole algorithm achieves.
Tracing values without updating a variable when it is reassigned.
Put it right: Overwrite the cell with the new value at the step where assignment occurs.
Ignoring the effect of a condition and assuming every branch runs.
Put it right: Follow only the branch whose condition is true for the given input.
Exam tips
- Set up the trace table before starting: one column per variable plus an output column.
- Work one step at a time and write the value after each assignment, not the expression.
- Finish by writing the purpose in a single sentence beginning 'This algorithm...'.
Try the lesson
The start of the Representing algorithms: Determine the purpose of simple algorithms. Students should be able to use trace tables and visual inspection to determine how simple algorithms work and what their purpose is. lesson, made from checked teaching notes for this specification point.
Have a go first
An algorithm repeatedly adds 1 to a counter until the counter reaches 10, then stops. What is the purpose of this algorithm?
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