SDD Past Paper Practice

Award 1 mark for: Iterative development process / software development process (accept "iterative" or "six-stage development process"). Must state 6 stages. Award 0 if only the name of one stage is given.

Example answer: The iterative development process — it has 6 stages: analysis, design, implementation, testing, documentation, and evaluation.

Award 1 mark each for two of:

• The process can repeat / go back to previous stages
• If a problem is found (e.g. during testing), the developer returns to an earlier stage (e.g. design or implementation)
• The process loops until the software meets all requirements
• Evaluation may identify new requirements, restarting the cycle

Award 1 mark for each of:

Input (1 mark): Pupil name / club name / number of places / pupil registration number (any reasonable input)

Process (1 mark): Check if places are available / add pupil to waiting list / count total members / search for a pupil's clubs (any reasonable process)

Output (1 mark): Confirmation that the pupil has been added / list of available clubs / number of remaining places (any reasonable output)

Award 1 mark each for two of:

• A specific thing the software must do / be able to do
• Describes the inputs, processes, and outputs required
• Comes from the client's specification / what the client asked for
• Something the developer can test — either the software does it or it doesn't

Example: "The program must accept a pupil's name and display a list of clubs they are registered for" is a functional requirement.

Award 1 mark each for:

• Repeats the score-collection process exactly 5 times
• Rejects scores outside 0–100 inclusive, displays an error, and asks again until valid
• Initialises the total to zero and adds each accepted score once
• Divides the final total by 5 and displays the average

Set total to zero
Start fixed loop 5 times
    Start conditional loop
        Get score from user
        If score is outside 0 to 100 display error message
    Repeat until score is between 0 and 100 inclusive
    Add score to total
End fixed loop
Calculate average as total divided by 5
Display average

Accept any clear, logically correct alternative design, including one that reads a score before a conditional loop. Assess the four behaviours above; particular keywords, indentation, loop-end spelling, or refinement numbering are not required.

Award 1 mark each for two of:

• Uses symbols for process, loop, selection, and predefined-process steps
• Represents the steps of an algorithm and how those steps are structured
• Is read from top to bottom and, where steps branch at the same level, from left to right
• Can show where repetition or selection occurs in the algorithm

A structure diagram is a design notation for algorithm steps; it is not a module-call hierarchy.

(a) 1 mark:

clubs = ["Art", "Chess", "Coding", "Drama", "Music", "Sport"]

(b) 1 mark:

print(clubs[2])

(index 2 = third element, because arrays/lists are zero-indexed in Python)

(c) 1 mark: Index 5. A 6-element array has indices 0–5. Last element = length − 1 = 6 − 1 = 5.

Award 1 mark for each of:

• A variable stores a single value; an array stores multiple values of the same type
• Array elements are accessed using an index (position number, starting at 0); a variable is accessed by its name alone

score = int(input("Enter score: "))
if score =< 0:
    print("too low)
elif score > 100
    print("too high")
else:
    print("Valid score")

Award 1 mark each for identifying and fixing:

• Error 1: =< is not valid Python. Fix: change to <= (less-than-or-equal-to).
• Error 2: Missing closing quote in "too low) — the string is not closed. Fix: "too low")
• Error 3: Missing colon at the end of elif score > 100. Fix: elif score > 100:

Award 1 mark for definition: A predefined function is a function that is already written and built into the programming language — the programmer can use it without having to write the code themselves.

Award 1 mark for benefit (any one):

• Saves time — the programmer does not have to write the code themselves
• Reduces errors — the function has already been tested and is reliable
• Improves readability — a single function call is easier to read than many lines of code
• Can be used multiple times in the same program without repeating code

scores = [45, 72, 88, 61, 53]
for _____ in range(_____):
    print(_____)

scores = [45, 72, 88, 61, 53]
for index in range(5):
    print(scores[index])

Award 1 mark for the loop variable and range (accept range(len(scores))); 1 mark for scores[index] (any valid index variable).

Alternative accepted: for score in scores: print(score) — award 2 marks.

(a) 3 marks — award 1 each for: initialising total to 0 before the loop; traversing every array element; updating total inside the loop.

temps = [12, 8, 15, 6, 19, 11, 14]
total = 0

for index in range(len(temps)):
    total = total + temps[index]

print("Total:", total)

(b) 1 mark: total values after each iteration: 12, 20, 35, 41, 60, 71, 85. Final output: Total: 85.

Award 1 mark each for:

• Gets the age from the user
• Correctly accepts ages 4–18 inclusive and identifies ages outside that range as invalid
• Repeats after invalid input, showing an error message and asking for another age

Start conditional loop
    Get age from user
    If age is outside 4 to 18 display error message
Repeat until age is between 4 and 18 inclusive

Accept any clear, logically correct alternative design, including a read-before-loop design. Check the logic rather than requiring particular keywords or layout. An age is invalid if it is below 4 or above 18; the two endpoints are valid.

Award 1 teacher-created practice mark for each of: the first update to 3, the next update to 2, and the final minimum of 2:

Final minimum = 2.

Award 1 teacher-created practice mark each for: a suitable normal test, a suitable boundary test, a suitable exceptional test, and correct expected outputs for all three.

Any reasonable test table accepted, as long as: at least one normal, at least one boundary, at least one exceptional, and expected outputs are correct.

Award 1 mark each for:

• Syntax error: A mistake in the grammar / spelling / punctuation of the code that prevents the program from running. Detected by the interpreter/compiler before execution. Example: missing colon, misspelled keyword, unmatched bracket.
• Logic error: The code runs without crashing but produces the wrong result. The programmer has made an error in the logic / algorithm. Example: using AND instead of OR in input validation, using < instead of <=.

x=int(input("?"))
if x>0:
    print("pos")
if x<0:
    print("neg")
if x==0:
    print("zero")

Award up to 2 marks for readability:

• No internal comments — a comment explaining the purpose of the program would improve readability
• Variable name x is not meaningful — should be renamed number or userValue
• Input prompt "?" is not descriptive — the user does not know what to enter
• No white space between the IF statements
• Output strings ("pos", "neg", "zero") are abbreviated and not meaningful to the user

Award up to 2 marks for efficient use:

• Three separate IF statements are used. This is inefficient because all three conditions are always evaluated.
• If x is 5 (positive), condition 1 is True — but conditions 2 and 3 are still checked unnecessarily.
• Using ELSE IF (elif) would be more efficient — once a match is found, the remaining conditions are skipped.

Unmarked PyCharm verification: the supplied code outputs neg, zero, and pos for separate inputs −3, 0, and 5 respectively. One improved implementation is:

# Classify an entered whole number.
number = int(input("Enter a whole number: "))

if number > 0:
    print("Positive")
elif number < 0:
    print("Negative")
else:
    print("Zero")

With −3, 0, and 5, the improved program displays Negative, Zero, and Positive respectively. Any equivalent improvement is acceptable.

Award 1 mark for identifying the problem: The program is not robust for negative numeric values. Calling math.sqrt() with a negative number raises ValueError, because the square root is not defined as a real number, and the program crashes.

Award 1 mark for suggesting an improvement: Validate the value so the program only calls math.sqrt() when number >= 0. One suitable Python rejection condition is while number < 0, with an error message and another numeric input inside the loop. Accept equivalent conditional-loop solutions.

Unmarked PyCharm implementation:

import math

number = float(input("Enter a non-negative number: "))
while number < 0:
    print("Invalid — number must be at least 0.")
    number = float(input("Enter a non-negative number: "))

print("Square root:", math.sqrt(number))

For −9 followed by 16, display Invalid — number must be at least 0. then Square root: 4.0. For 0 immediately, display Square root: 0.0. Without validation, math.sqrt(-9) raises ValueError.