Paper 2 (9618/21) Oct/Nov 2024

Which keyword replaces a final CASE condition to catch anything unmatched?

OTHERWISE

What are the general steps to output the last 3 lines of a file, in order?

• Open file for reading

• Loop until end of file

• Read line into a temporary variable

• Shift previous values: LineX ← LineY, LineY ← LineZ

• Assign new line: LineZ ← ThisLine

• Close file

• Output LineX, LineY, LineZ

Why are the variables shifted (LineX ← LineY, etc.) when reading a file?

To ensure that only the last three lines are stored, in the correct order for final output.

How can you modify a file-reading algorithm to output 3 lines starting from a specific line number?

• Loop until you reach the starting line (check for EOF and return FALSE if reached early)

• Then read 3 lines (again, return FALSE if EOF is reached too soon)

• Output each line

• Return TRUE if successful

What type of error occurs when a program runs but crashes due to bad input? Give a cause.

• Type: Run-time error

• Cause: Invalid input or action, e.g., division by zero or converting a non-numeric string to a number.

Give one reason to use a module for repeated logic and state what this avoids.

• Reason: Makes the program easier to test, debug, and maintain — change logic in one place only.

• Avoided: Code duplication and inconsistent logic across the program.

Match these activities to their life cycle stages:

Activity	Life Cycle Stage
Interview client about system
Write code
Define records/files
Use walkthrough method
Modify for new hardware

Activity	Life Cycle Stage
Interview client about system	Analysis
Write code	Coding
Define records/files	Design
Use walkthrough method	Testing
Modify for new hardware	Maintenance

What type of testing is done on individual modules before combining them?

• Integration testing (when combining modules)

• Unit testing (if testing a single function on its own before integration)

(Note: Mark scheme said “integration,” but if the function is tested before combining, it’s “unit.”)

Give two advantages of using arrays instead of multiple selection statements.

1. Fewer lines of code — cleaner, shorter logic.

2. Easier to modify or maintain — values are stored in a single location and can be accessed using indexes.

What are the key components to include when drawing a structure chart for a program with subroutines?

• Show all modules in the correct hierarchy (e.g., top-down: main procedure → subroutines)

• Include parameters for each call (use arrows or labels)

• Show return values from functions

• Use curved arrow to represent repetition or recursion

• Connect modules using single lines (not multiple arrows)

If a file needs to be updated by adding data (not overwritten), what must change?

Open the file in APPEND mode instead of WRITE mode

What is a local variable?

• A variable declared inside a subroutine

• Can only be accessed and used within that subroutine

Give one reason to use local variables in subroutines.

• Prevents conflicts with variables in other parts of the program

• Makes subroutines more modular, self-contained, and easier to debug