Exception Handling (Cambridge International A-Level Computer Science)

Exam board Cambridge International · A-LevelUpdated 2025-05-21

An exception is an unexpected event that disrupts normal program execution
Exception handling is how a program detects and responds to these errors, allowing it to recover or shut down cleanly

Prevents programs from crashing unexpectedly
Allows for user-friendly error messages
Makes programs more robust and reliable
Handles problems caused by:
- Division by zero
- File not found or end-of-file errors
- Hardware or device failures (e.g. printers, lost connections)
- Invalid input from users

Cause	Example
Programming errors	Uninitialised variables, logic errors
User errors	Entering text instead of a number
Hardware failure	Lost connection to printer, disk error

Keyword	Purpose
`TRY`	Starts a block of code that may raise an error
`EXCEPT`	Executes if an error occurs in the `TRY` block
`ENDTRY`	Marks the end of the exception handling structure

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Cause

Example

Programming errors

Uninitialised variables, logic errors

User errors

Entering text instead of a number

Hardware failure

Lost connection to printer, disk error

Keyword

Purpose

TRY

Starts a block of code that may raise an error

EXCEPT

Executes if an error occurs in the TRY block

ENDTRY

Marks the end of the exception handling structure