Inputs; processing and outputs
Inputs, Processing and Outputs
Every algorithm can be understood by breaking it into three stages: input, processing, and output - often called the IPO model. Understanding these three stages is a fundamental skill for reading, writing, and explaining algorithms.
- Input - the data the algorithm receives before it begins working. This could come from a user typing, a file being read, or a sensor.
- Processing - what the algorithm does with that data: calculations, comparisons, decisions, or transformations.
- Output - the result that the algorithm produces after processing is complete. This could be displayed on screen, saved to a file, or passed to another part of a program.
Identifying these three stages in any algorithm helps you understand its purpose before worrying about its code.
IPO in Practice
The three tabs below each show a simple algorithm. For each one, the input, processing, and output have been clearly identified. Study each example and notice how the three stages map onto the steps of the algorithm.
Algorithm: Ask the user for two numbers. Add them together. Display the result.
| Stage | What happens |
|---|---|
| Input | Two numbers entered by the user |
| Processing | The two numbers are added together to calculate a total |
| Output | The total is displayed on screen |
Algorithm: Ask the user for a temperature in Celsius. Multiply it by 1.8 and add 32. Display the result in Fahrenheit.
| Stage | What happens |
|---|---|
| Input | A temperature value in Celsius entered by the user |
| Processing | The formula (Celsius × 1.8) + 32 is applied to convert the temperature |
| Output | The equivalent temperature in Fahrenheit is displayed |
Algorithm: Ask the user for a test score. If the score is 50 or above, display "Pass". Otherwise, display "Fail".
| Stage | What happens |
|---|---|
| Input | A test score entered by the user |
| Processing | The score is compared against the threshold of 50 to decide the outcome |
| Output | "Pass" or "Fail" is displayed depending on the result of the comparison |
Notice that the processing stage here involves a decision, not a calculation. Processing can take many forms - what matters is that it transforms or evaluates the input in some way.
Key Takeaways
- Every algorithm has three stages: input (data received), processing (what is done with it), and output (the result produced).
- Processing can be a calculation, a comparison, a decision, or a transformation - any operation that acts on the input data.
- Identifying IPO stages is a way of explaining an algorithm's purpose without needing to trace every line of code.
- An algorithm may have more than one input and more than one output - always identify all of them.
- The output of one algorithm can become the input of another - this is how larger programs are built from smaller parts.