Iteration: Loops

What is Iteration: Loops?

Within Computer Science, which covers algorithms, programming, data, networks, hardware and safe, responsible use of technology, this topic explains Iteration: Loops. Computing topics explain how software, hardware and data work, with diagrams and models that show each step in order.

Check that you can explain Iteration: Loops in your own words and give one example from everyday life. If you can do that, you have understood the core idea.

Understanding Iteration: Loops helps you design, test and explain programs, websites and systems, from small projects to exam questions.

Iteration: Loops in detail

Iteration repeats a block of code. A FOR loop (count-controlled) repeats a set number of times, such as for i in range(5). A WHILE loop (condition-controlled) repeats as long as a condition is true, checking before each pass, and a REPEAT...UNTIL loop checks at the end, so it runs at least once.

Loops avoid repeating code, process lists, validate input and run games. An infinite loop never ends, caused by a condition that never becomes false, which is a common bug. Loops can be nested for tasks such as grids. Counters and accumulators are used to keep track of totals.

How the interactive helps you understand Iteration: Loops

Watch the cycle in the interactive. Use any sliders or buttons it offers to change the values and see how the cycle responds.

Before you change anything, predict the result. Then change one value at a time and check whether your prediction was right. This is a quick way to build a correct mental model of Iteration: Loops.

Real-life uses and examples

• Recognise Iteration: Loops in an app or device you use every day.
• Apply Iteration: Loops when you design a small program, website or spreadsheet.
• Explain Iteration: Loops to someone new to computing by comparing it to a familiar process.

Common mistakes to avoid

• Using the term without being able to say what the computer actually does.
• Testing only the normal case and forgetting the edge cases.
• Learning the definition without testing it. Use the quiz and the interactive to check that you can apply the idea.