Stretch tasks Robust and Secure Programming

Round 1: Quiz Blitz

1. That data is reasonable Validation checks plausibility. It cannot detect a lie.
2. Look up check A look up check accepts only values in a known set.
3. False 01/01/1990 passes every check, and is wrong for someone born in 1991.
4. Who are you? Validation answers whether a value is sensible.
5. Locking the account after several failed attempts; Two factor authentication Minimum lengths and asking for characters from a memorable word help too.
6. Runtime error It starts, then stops while executing.
7. A logic error It runs, but gives the wrong answer at the boundary, and nothing reports it.
8. -1; 121 0 and 120 are on the boundary. -1 and 121 are just outside it.
9. erroneous Erroneous data checks that the validation works.
10. # skip the header row of the file A useful comment explains why, not what.
11. True Module by module, while the code is still fresh and small.
12. Show a message saying what went wrong and what to do A clear message lets the user recover. A crash does not.

Round 2: Quick Fire

1. • Validation only checks that data is reasonable
   • A wrong value, such as a mistyped date of birth, can still pass every check
   Model answer

   Validation only checks that data is reasonable. A wrong value, such as a date of birth that is a year out, can still pass every check.

2. • Authentication checks a user is who they claim to be
   • Validation checks that input data is reasonable
   Model answer

   Authentication checks that a user is who they claim to be, for example with a password. Validation checks that the data entered is reasonable.

3. • Normal: a typical age
   • Boundary: an age on or just outside a limit
   • Erroneous: data that should be rejected
   Model answer

   Normal: 35. Boundary: 120. Erroneous: "cat".

4. • Meaningful identifiers, such as totalPrice instead of tp
   • Comments that explain why
   • Indentation that shows the structure
   • Subroutines, so each task is in one place
   Model answer

   Use meaningful identifiers, such as totalPrice instead of tp, and add comments that explain why the code does something, not what it does.

Round 3: Big Think

1. • A syntax error breaks the rules of the language, so it will not run
   • Syntax example: a missing bracket or misspelled keyword
   • A logic error runs but gives the wrong result
   • Logic example: + where - was meant, or < instead of ≤
   • A runtime error stops the program while it runs
   • Runtime example: dividing by zero, or reading past the end of an array
   Model answer

   A syntax error breaks the rules of the language, such as a missing bracket or a misspelled keyword, so the program will not run at all. A logic error means the program runs but gives the wrong result, such as using + where - was meant. A runtime error happens while the program is running and stops it, such as dividing by zero or reading past the end of an array.

2. • Normal data the program should accept
   • Boundary data on both sides of each limit
   • Erroneous data the program should reject
   • Boundaries are where off by one bugs show up
   • Iterative testing finds faults early, during development
   • Final testing checks the whole program against the requirements
   Model answer

   Test data should include normal data, such as a valid username, which should be accepted; boundary data on both sides of each limit, such as a password of exactly the minimum length and one character shorter; and erroneous data, such as a blank entry, which should be rejected. Boundaries matter most, because off by one bugs show up there and nowhere else. Iterative testing during development finds faults early, when they are cheap to fix, and final testing checks the whole program against the original requirements.

This or That

1. Verification Verification checks data was entered accurately.
2. Format check It checks the data matches a pattern.
3. Length check It counts characters, not the size of a number.
4. A syntax error Nothing reports a logic error: the program just gives the wrong answer.
5. On both sides of the limit Test 120 and 121, and 0 and -1.
6. totalPrice Meaningful names make code maintainable.
7. Something you have Such as a code sent to your phone.
8. Before doing anything sensitive Authenticate before acting, not after.

Memory Match

• A 6 Range check: Between two limits
• B 3 Presence check: Something was entered
• C 2 Look up check: One of a known set of values
• D 5 Syntax error: Breaks the language's rules
• E 1 Runtime error: Stops while the program runs
• F 4 Erroneous data: Data that should be rejected

Sort It

1. Erroneous An empty entry Nothing was entered, so it must be rejected.
2. Boundary -1 Just outside the lower limit: test both sides of a boundary.
3. Boundary 120 On the upper limit.
4. Boundary 0 On the lower limit.
5. Normal 12 A normal, valid age.
6. Boundary 121 Just outside the upper limit.
7. Erroneous 3.5 An age must be a whole number.
8. Normal 35 A typical age that should be accepted.
9. Normal 64 Comfortably inside the range.
10. Erroneous "twenty" A word, not a number.
11. Erroneous "cat" Not a number at all, so it must be rejected.