Paper 2 exam skills

Paper 2: Computational thinking, algorithms and programming covers sections 2.1 to 2.5. It's 80 marks in 1 hour 30 minutes, half your GCSE, without a calculator, in two sections:

• Section A (50 marks, about 50 minutes): concepts, and applying them to problems, perhaps with an algorithm.
• Section B (30 marks, about 40 minutes): designing, writing, testing and refining programs.

Allow about a minute a mark.

In Section A, the logic matters, not the syntax. You can answer an algorithm question in pseudocode, a flowchart, bullet points, plain English, ERL or Python.

Question: Write an algorithm that asks for a whole number and outputs whether it is even or odd. [3]

As bullet points:

• Ask the user for a whole number.
• If the remainder when it's divided by 2 is 0, output "Even".
• Otherwise, output "Odd".

As a flowchart:

In ERL and Python:

number = int(input("Whole number?"))
if number MOD 2 == 0 then
    print("Even")
else
    print("Odd")
endif

number = int(input("Whole number? "))
if number % 2 == 0:
    print("Even")
else:
    print("Odd")

Each earns the same 3 marks: an input, a correct check for even, and both outputs.

Section B's questions are often built around one scenario. Here's an original one, used for each question style below.

Scenario: a cinema charges £6 for children under 12, £7 for people aged 65 or over, and £10 for everyone else. It wants a program that works out ticket prices.

Question: Identify the inputs, processes and outputs of the ticket program, and a suitable data type for the input. [4]

Model answer:

What gets the marks: a mark for each correct, relevant point. A data type needs a reason linked to the data. Design answers can be in plain English, pseudocode or a flowchart: the code comes later.

Question: Write a function, ticket_price, that takes a person's age as a parameter and returns the price of their ticket. You must use either OCR Exam Reference Language or a high-level programming language. [4]

Model answer:

function ticket_price(age)
    if age < 12 then
        return 6
    elseif age >= 65 then
        return 7
    else
        return 10
    endif
endfunction

def ticket_price(age):
    if age < 12:
        return 6
    elif age >= 65:
        return 7
    else:
        return 10

What gets the marks:

• a function with an age parameter;
• the under-12 check, with the right boundary (< 12);
• the 65-or-over check (>= 65);
• returning the right price in every case, rather than printing it.

Minor syntax slips, such as a missing colon, aren't penalised, but each construct must be recognisable: strings in quotation marks, = for assignment, and names with no spaces.

Question: Complete the test plan for the ticket program, which should accept ages from 0 to 120. [4]

Model answer:

What gets the marks: test data of the type asked for, each with the right expected result. Boundary data tests each side of every boundary, as that's where mistakes such as < instead of <= show up.

Question: This program works out the cost for exactly three people. Refine it so it works for any number of people. You must use either OCR Exam Reference Language or a high-level programming language. [4]

total = 0
age = int(input("Age of person 1?"))
total = total + ticket_price(age)
age = int(input("Age of person 2?"))
total = total + ticket_price(age)
age = int(input("Age of person 3?"))
total = total + ticket_price(age)
print("Total: £" + str(total))

Model answer:

people = int(input("How many people?"))
total = 0
for i = 1 to people
    age = int(input("Age?"))
    total = total + ticket_price(age)
next i
print("Total: £" + str(total))

people = int(input("How many people? "))
total = 0
for i in range(people):
    age = int(input("Age? "))
    total = total + ticket_price(age)
print("Total: £" + str(total))

What gets the marks: asking how many people; a loop that runs that many times; adding each price to the total inside the loop; and printing the total after it.