Describe algorithms with inputs, processes, outputs and storage
Explain what an algorithm does by identifying the data it receives, steps it performs, results it produces and information it retains.
Section 7 · Algorithm design and problem-solving
This sequence follows Cambridge IGCSE Computer Science 0478, 2026–2028 syllabus Version 6. It covers subject content Topic 7 only. The separately published 2029–2031 syllabus is not mapped here. Practice is original, self-checked and does not award an official Cambridge grade. Full timed papers and human subject-teacher review remain outstanding.
Before you begin
- No programming language is required. Be comfortable with place value and multiplication; each lesson introduces the computer-science notation it uses.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does an algorithm describe?
What you will learn
- State an algorithm's purpose
- Identify input, process, output and storage
- Describe the sequence of operations
An algorithm is a planned sequence of steps
An algorithm gives a finite, ordered set of instructions for solving a problem. When describing its purpose, state the problem it solves and what result it produces.
Apply and check the rule
Analyse the algorithm using inputs, processes, outputs and storage. Inputs are supplied data; processes transform or compare it; outputs are results or messages; storage retains values for later steps or future use.
Pause and explain
A program stores a student's ID so a later step can retrieve it. Which category is this?
Worked example
An algorithm reads three scores, finds their average, displays it and saves the result. Classify each part.
Show the worked solution
- Inputs: three scores.
- Process: add and divide by three.
- Output: displayed average; storage: saved average.
Answer It inputs three scores, calculates their mean, displays the mean and stores it for later use.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
For an algorithm that converts minutes to hours and remaining minutes, identify one input, one process and two outputs.
Give me a hint
Use division and remainder to split the value.
Compare my reasoning
- Input: total minutes.
- Process: divide by 60 and find the remainder.
- Outputs: whole hours and remaining minutes.
Input total minutes; calculate total DIV 60 and total MOD 60; output hours and remaining minutes.
Look for these in your work
- Input
- Process
- Two outputs
An algorithm stores a running total between loop iterations. Explain why the total is storage rather than a final output.
Give me a hint
Consider whether a user receives it or the algorithm uses it later.
Compare my reasoning
- The variable retains a value between steps.
- The next iteration reads and updates it.
- It becomes an output only if the algorithm displays or returns it.
The running total is stored state used by later iterations. It is an output only if the algorithm presents it as a result.
Look for these in your work
- Retained state
- Later use
- Output distinction
A description says an algorithm “processes orders.” Rewrite it to state its purpose and name its inputs, process, outputs and storage.
Give me a hint
Make the high-level purpose observable.
Compare my reasoning
- Inputs can include order items and customer details.
- The process checks availability and calculates the total.
- Outputs can be confirmation or an error; storage retains the order record.
Purpose: accept valid orders and tell the customer whether they were accepted. Inputs are items and details; processing checks availability and calculates a total; outputs are confirmation or a reason for rejection; storage retains accepted orders.
Look for these in your work
- Purpose
- Input and process
- Output and storage
Common mistakes
- Calling a calculation an output before it is displayed or returned
- Ignoring data saved for later use
What can you explain now?
What is an output?
Compare with the explanation
A result or message produced by the algorithm
The output is information made available after processing.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
How do input, process, output and storage help explain an algorithm's purpose?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.