GCSE (9-1) Computer Science
Mark Scheme
J277/02: Unit 2.3 Robust Programs
Question Answer Marks Guidance
1 (a) Normal (1)
(b) Invalid (or Boundary Invalid) (1)
(c) Erroneous (1) 		3
"Invalid" is the standard term for wrong range but correct type.
2 (a) 11 (1)
(b) Invalid (or Boundary Invalid) (1)
(c) Erroneous (1) 		3
Strict: (a) Must be exactly 11. 10 or 12 are incorrect.
Do not accept "Erroneous" for 19 (it is the right type, just wrong range).
3 (a) It is too vague / It does not explain what is being tested. (1)
(b) To check that a password shorter than 6 characters (5 chars) is rejected. (2) 		3
Must mention "Length", "Short", or the specific character count. "To see if it works" is never credited.
4 (a) "ABCDE" (Any string exactly 5 chars long) (1)
(b) "ABCDEFGHIJ" (Any string exactly 10 chars long) (1)
(c) Error message displayed / User asked to input again. (2) 		4
The content of the string doesn't matter, only the length.
0 Marks for "Program crashes" or "Nothing happens". Robust programs do not crash.
5 (a) Runtime Error (or Execution Error) (1)
(b) num = input("Enter number")
if num.isnumeric(): (or try/except) (1)
  x = int(num) (1)
else: print("Invalid Input") (1) 		4
The key is using logic (try/except or isnumeric check) to prevent the conversion crash.
6 (a) It does not handle the number 16 (gap in logic). (1)
(b) Nothing / Blank / No Output (1)
(c) Entering 16 is the exact boundary (1). It would show the programmer that 16 produces no result, highlighting the missing = sign. (1) 		4
age < 16 and age > 16 leaves 16 undefined. Neither if nor elif is triggered.
7 (a) Should be: Invalid (1). Reason: It is the correct data type (Integer) but outside the range. (1)
(b) Should be: Erroneous (1). Reason: It is the wrong data type (String input for Integer field). (1) 		4
J277 Definition: Invalid = Right type, wrong range. Erroneous = Wrong type.
OCR 2026