Cambridge Syllabus Notes

12.3 Program Testing and Maintenance

Locate and identify the different types of errors that can occur in a program. 🧩

Error Type	What It Looks Like	Analogy	Example
Syntax Error	Compiler or interpreter stops with a message like “unexpected token”.	Like a sentence that breaks the rules of grammar.	`if (x > 5 {` ← missing parenthesis.
Runtime Error	Program crashes or throws an exception while running.	Like a car that stalls when you hit the accelerator.	`int a = 5 / 0;` ← division by zero.
Logical Error	Program runs but gives wrong results.	Like following a recipe but swapping salt for sugar.	`if (score >= 60) { pass = true; }` ← should be `>= 50`.

Syntax Errors: Read the compiler’s error message carefully. It usually points to the line and the exact token that caused the problem. 🛠️
Runtime Errors: Use a debugger or add print statements to see where the program stops. Look for operations that can fail (division, file I/O, null references). ⚠️
Logical Errors: Verify the program’s output against expected results. Write test cases for edge conditions (e.g., 0, negative numbers, maximum input). 🔍

Read the question carefully: it often hints at the error type (e.g., “the program crashes” → runtime).
Show the error message or the line number if you can. It demonstrates you understand the compiler’s feedback.
Explain why the error occurs and how you would fix it. Use the analogy to make your answer memorable.
When writing code snippets, keep them short and to the point. Use comments to explain the bug.

Error	Typical Message	Fix
Syntax	“Unexpected identifier”	Check brackets, commas, and spelling.
Runtime	“Division by zero”	Add a guard: `if (denominator != 0)`.
Logical	Program runs but output is wrong.	Re‑evaluate the algorithm or conditions.