Edexcel 1CP2 6.1.5: Finding and correcting errors
The free BugBot lessons that teach this point, a robot to try it on, and the past-paper questions that test it.
What it covers
Syntax errors and runtime errors announce themselves. A logic error does not: the program runs, finishes, and does the wrong thing. Finding one is detective work, and like detective work it goes faster with a method. This lesson is that method, and the tools that help.
- Step 1: know what should happen
- Step 2: find where it first goes wrong
- Step 3: form a theory and test it
- Common logic errors
- Explaining it out loud
Or do it in the simulator, with tasks that mark themselves
Lessons that teach it
- F6.4 Debugging logic errors Robust programs
Finding the mistake that gives no message: watching, printing, stepping and common bugs. - F6.6 The IDE Robust programs
Editors, error diagnostics, the run-time environment and the translator, in the cell you use.
Try it on a robot
The task from F6.4 Debugging logic errors, running here. Change the program and press Run.
Past paper questions on this
Real exam questions that test this, each worked through with a program you can run.
- AQA 8525 June 2025 Paper 1, Question 9: Which of five algorithms correctly total an array 2 marks
- AQA 8525 June 2023 Paper 1, Question 10: Trace nested FOR loops over a list of scores and find the error 6 marks
- AQA 8525 June 2023 Paper 1, Question 11: Normal, erroneous and boundary test data, and a logic error 5 marks
- AQA 8525 June 2022 Paper 1, Question 5: A syntax error and a logic error in a random number program 5 marks
- AQA 8525 Sample Paper 1, Question 15: Fix a loop that prints odd numbers so that it works for negative input 4 marks
- AQA 8525 Sample Paper 1, Question 17: The highest common factor program that fails for 4 and 4 3 marks
- OCR J277 June 2024 Paper 2, Question 3(a), (b): Define a syntax error, then correct two logic errors in a range check 6 marks
- OCR J277 June 2023 Paper 2, Question 2: Syntax and logic errors: correct a loop that should total an array 6 marks
- OCR J277 June 2022 Paper 2, Question 5(d): Two logic errors in a loop that totals an array 2 marks
- Edexcel 1CP2 June 2025 Paper 2, Question 1: Fix nine errors in a program that discounts a restaurant bill 9 marks
- Edexcel 1CP2 June 2023 Paper 2, Question 2: Fix syntax, name, index and logic errors in a program that picks random exercises 8 marks
- Edexcel 1CP2 June 2022 Paper 2, Question 2: Fix ten errors in a turtle graphics program 10 marks
The specification is Edexcel's own document; this page says which of our lessons teach point 6.1.5 and is not endorsed by the board.