Producing Robust Programs

What Producing Robust Programs covers

Producing Robust Programs is examined in J277/02, Computational thinking, algorithms and programming. It covers defensive design, input validation and authentication, writing maintainable code and testing, errors and test data.

The 3 subtopics

Each one has its own page.

• Defensive design, input validation and authenticationDefensive design and anticipating misuse, presence, length, range, type and format checks, validation loops, verification, and authentication in a login routine.Open →
• Writing maintainable codeWhy maintainability matters, sub programs, naming conventions and camel case, constants, indentation and comments, and what makes code easy for others to update.Open →
• Testing, errors and test dataIterative and final testing, syntax and logic errors, normal, boundary, invalid and erroneous test data with worked examples, and writing a test plan.Open →

What you need to know

Answer each one before you reveal it.

Take Producing Robust Programs further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Validation vs Verification

  Validation: an automatic check that input obeys set rules before it is accepted. Verification: a check that data was entered or copied exactly as intended.

• Syntax error vs Logic error

  Syntax error: a mistake in the grammar of the code that stops it being translated. Logic error: a mistake that lets code run but gives an unexpected result.

• Iterative testing vs Final testing

  Iterative testing: checking each module repeatedly while the program is still being developed. Final testing: checking the complete program once development has finished.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What is defensive design?

   Model answer

   Defensive design means planning a program so it copes with every likely input and with misuse. The program should keep working and stay secure.

2. 2

   What does anticipating misuse involve?

   Model answer

   A programmer predicts how users might misuse the program, by mistake or on purpose. The code is then written to handle each case safely.

3. 3

   Give three ways a user might misuse a program that asks for their age.

   Model answer

   A user might leave the input blank. A user might type letters such as "ten". A user might enter an impossible value such as −5 or 250.

4. 4

   What is input validation?

   Model answer

   Input validation is an automatic check that data follows set rules before the program accepts it. Data that fails the check is rejected and the user is asked again.

5. 5

   What does a range check test?

   Model answer

   A range check tests that a value lies between a lowest and a highest limit. An example is a percentage that must be from 0 to 100.

6. 6

   What do a presence check and a length check test?

   Model answer

   A presence check makes sure a field has not been left empty. A length check makes sure the input has an allowed number of characters, such as at least 8.

What is inside Levo

Six ways to work the same material.

Producing Robust Programs revision questions

What does Producing Robust Programs cover in OCR GCSE Computer Science?

3 subtopics: defensive design, input validation and authentication, writing maintainable code and testing, errors and test data. Each one has its own page with questions and model answers.

How is Producing Robust Programs organised?

By the OCR J277 specification, subtopic by subtopic, so it matches the order you are taught it in.