AQA GCSE Computer Science Paper 1 (1A), June 2025: Question 2

✅ Correct Answers (1 mark each)

• L1: i % 5 == 0
• L2: Console.WriteLine("Free pastry"); or Console.Write("Free pastry");
  Wait! Ensure you read the question labels carefully:
  • In the code, pastry is already printed for L1. Label L2 is inside else if (i % 4 == 0) , so:
  L2: Console.WriteLine("Free biscuit");
• L3: Console.WriteLine("Nothing free");

💡 Key Knowledge: The Modulo Operator (%)

The modulo operator gives the remainder after integer division:

• i % 5 == 0 evaluates to true whenever i is a multiple of 5 (e.g. 5, 10, 15, 20).
• Order matters in selection: Notice that the code checks i % 20 == 0 first. Because 20 is divisible by both 4 and 5, checking it first prevents customers getting a biscuit or pastry instead of their free cake!

🧠 Exam Technique & Mark Scheme Notes

• Console is optional: Examiners allow omitting Console. (e.g. just writing WriteLine("Free biscuit"); ), but writing full syntax guarantees you avoid ambiguity.
• Case insensitivity: The mark scheme ignores letter casing errors for methods, but getting into the habit of typing exact PascalCase ( WriteLine ) is best practice.
• No missing parentheses: Don't drop parentheses around condition expressions or method parameters.

❌ Common Errors to Avoid

• Assignment vs Comparison: Writing i % 5 = 0 instead of == 0 . A single equals sign assigns; double equals tests equality.
• Division instead of Modulo: Writing i / 5 == 0 . 5 / 5 gives 1, not 0!
• Swapping L2 and L3: Always check which condition matches which branch: condition i % 4 == 0 corresponds to the free biscuit!

📐 Step-by-Step Logic Breakdown

1. Step 1: Get Inputs
   Prompt or directly read three user inputs from the console. Convert each string to an integer using Convert.ToInt32() or int.Parse() .
2. Step 2: Apply Unit Values
   • Biscuits: £1 each ( biscuits * 1 )
   • Pastries: £2.50 each ( pastries * 2.5 )
   • Cakes: £3 each ( cakes * 3 )
3. Step 3: Sum the Subtotals
   Add all three together to compute the overall total value.
4. Step 4: Output the Result
   Print the total using Console.WriteLine(totalValue); .

💡 Data Types Matter

• String to Number: Console.ReadLine() returns text ( string ). You cannot do arithmetic directly with strings.
• Floating-point calculations: Pastries cost £2.50 (a decimal), so the total must be stored in a type capable of holding decimals (e.g. double or float ).
• Note: In AQA GCSE mark schemes, explicit type declarations at the start of variables are leniently assessed, but proper syntax avoids losing marks.

🧠 Mark Scheme Breakdown

• Mark A: Taking user input and storing it in a variable for at least one item.
• Mark B: Taking input and storing into three distinct variables for biscuits, pastries, and cakes.
• Mark C: Correct mathematical expression to calculate the total value.
• Mark D: Outputting the calculated total.
• Crucial Examiner Rule: Maximum 3 marks if there are any syntax errors anywhere in the code. To get 4/4, your code must be completely error-free!

❌ Common Traps

• Forgetting Conversion: Writing biscuits = Console.ReadLine(); without parsing causes a type mismatch error.
• Wrong Math Multipliers: Mixing up the prices (e.g. multiplying cakes by 2.5 and pastries by 3).
• Missing Semicolons: In C#, every instruction statement must end with a semicolon ( ; ). Missing even one can cap you at 3 marks!