H446 Revision

2.1.2

Thinking ahead

Exam questions: 10 questions, 83 marks

Question 1

4 marks

1

A group of students are designing a racing car game. The game will allow players to enter their name and then a choice of vehicle. They will then race against other vehicles that will be controlled by the program. Players will use the arrow keys to control their vehicle.

The students are identifying the inputs and outputs for the game.

Complete the table by identifying two inputs and two outputs for the game.

Input 1…… ……
Input 2…… ……
Output 1…… ……
Output 2…… ……
Mark scheme 1

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark for each input to max 2 e.g.

  • Entering a name

  • Selecting a vehicle

  • Pressing arrow key to move forward

  • Pressing arrow key to move backward

  • Pressing arrow key to move left

  • Pressing arrow key to move right

1 mark for each output to max 2 e.g.

  • Images of vehicles to choose from

  • Background of area

  • Image of other vehicles

  • Image of controls and description of what they do

Guidance

Allow any feasible input/output for scenario

Examiner’s Comments

While many candidates scored full marks for this question for identifying suitable inputs and outputs within the context of the problem a number of candidates scored no marks for erroneously giving input or output devices. Sometimes responses were unqualified such as ‘left arrow key’ rather than ‘left arrow to turn left’ where candidates did not identify an input within the context of the scenario as an input to the game.

out of 4

Question 2

3 marks

2

A program is being designed that will allow a user to log into an account on a website using a username and password.

Identify two possible inputs and one output this program will need.

Input 1

Input 2

Output

Mark scheme 2

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark for each input to max 2

  • Username

  • Password

1 mark for output
e.g.

  • Message to request input

  • Message to state login successful

  • Message to say login unsuccessful

Guidance

Examiner’s Comments

This question was generally well answered by most candidates, but answers had to be given in the context of the scenario. Some less successful responses mistakenly identified input/output devices rather than specific examples of inputs and outputs.

out of 3

Question 3

5 marks

3(a)

A programmer has designed a program that includes a reusable program component.

The reusable program component is a function called isInteger(). This will take a string as an argument and then check that each digit is between 0 and 9. For example if 103 is input, it will check that the digits 1, 0 and 3 are each between 0 and 9.

The asc() function returns the ASCII value of each digit. For example asc("1") returns 49.

The ASCII value for 0 is 48. The ASCII value for 9 is 57.

01   function isInteger(number)
02     result = true
03     for count = 0 to number.length-1
04       asciiValue = asc(number.substring(count, 1))
05         if not(asciiValue >= 48 and asciiValue <= 57) then
06         result = false
07       endif
08     next count
09     return result
10   endfunction

3(a)(i)

Identify one identifier used in the function isInteger().

Mark scheme 3(a)(i)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark for:

• isInteger
• number
• result
• count

• asciiValue

Guidance

Penalise excessive spaces in identifiers such as ascii Value
instead of asciiValue

Examiner’s Comments

This question was generally well done (although slightly less well done than parts (a) (ii) and (a) (iii)), but many candidates did very well. The most common erroneous responses were giving the names of predefined
functions/properties or giving relational operators.

out of 1

3(a)(ii)

Give the line number where the branching (selection) construct starts in the function isInteger().

Mark scheme 3(a)(ii)

(0)5

Guidance

Examiner’s Comments

This question required an exact answer only and was answered correctly by the majority of candidates.

3(a)(iii)

Give the line number where the iteration construct starts in the function isInteger().

Mark scheme 3(a)(iii)

(0)3

Guidance

Examiner’s Comments

This question also required an exact answer only and was answered correctly by the majority of candidates.

3(b)

Give two reasons why reusable program components are used in programs.

1

2

Mark scheme 3(b)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark each to max 2:

  • One piece of code can be used many times / in multiple places / makes code more efficient

  • No need to write the same code multiple times

  • Takes less time to plan/design/code the program

  • Easier error detection as fix once and it corrects in each place / less likely to have errors as code is not written multiple times

  • Makes it easier to maintain the program

Guidance

Examiner’s Comments

Many less successful responses gave vague generalities such as ‘saves time’ or ‘more efficient’ without specifying why or how. Points given must be qualified in some way at A Level. For example, ‘saves development time as pre- written routines are available’.

Pre-written or pre-tested, and saving development time due to already being written, were the most popular answers.

out of 2

Question 4

4 marks

4

Taylor is designing a program for a client who would like to simulate earthquakes on major cities around the world in 3D. The client would like to be able to view any stage of an earthquake such as:

  1. the build-up of the earthquake\
  2. the earthquake taking place\
  3. the aftershocks of the earthquake.
    The client would also like to be able to play the simulation at different speeds. For example, a slow, normal or fast speed.

The program will need to accept inputs from the user before playing the simulation.

4(i)

Identify two different inputs for this program.

1

2

Mark scheme 4(i)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark per bullet e.g.

  • stage (e.g. stage 1, stage 2, stage 3)

  • city name (e.g. London)

  • speed (e.g. slow, normal, fast)

Guidance

Examiner’s Comments

Most candidates
successfully identified the relevant potential inputs of city/stage/speed from the given scenario. Some

candidates suggested alternative inputs such as ‘magnitude of earthquake’ which were also given marks as they were valid inputs for a simulation relating to earthquakes.

out of 2

4(ii)

One decision point in the program will be to decide if the user inputs are suitable or not.

Identify two other example decision points in this program.

1

2

Mark scheme 4(ii)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark per bullet to max 2, e.g.

  • Does the build-up stage need to be shown?

  • Does the earthquake taking place needs to be shown?

  • Does the aftershock stage needs to be shown?

Guidance

Allow other suitable examples

Examiner’s Comments

Few candidates were given full marks for this question. There was some repetition of checking user input values, which was given in the stem of the question. There were also many statements of possible calculations rather than clearly expressed conditions or questions. More successful responses included decisions such as ‘have buildings of a certain typ e survived the earthquake?’.

out of 2

Question 5

9 marks

5

A programmer has partially developed a bubble sort algorithm in pseudocode.

This will partially sort an array of numbers called numbers that is passed as a parameter.

01 procedure bubbleSort(numbers : byRef)
02   flag = true
03   for x = 0 to numbers.length – 1
04     if numbers[x] > numbers[x + 1] then
05       holdValue = numbers[x]
06       numbers[x] = numbers[x + 1]
07       numbers[x + 1] = holdValue
08       flag = false
09     endif

10   next x
11 endprocedure

5(i)

Explain why the procedure bubbleSort accepts the array numbers by reference and not by value.

Mark scheme 5(i)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark per bullet

  • by reference will reorder the contents of the array

  • …so the new order can be accessed by the main program / so will be saved when the procedure ends

  • by value will change the array only in this procedure

  • … and so would need to return the array.

Guidance

Examiner’s Comments

Many candidates struggled to go beyond recall of definitions for calling by reference and calling by value and struggled to apply it to the code given and to provide a detailed explanation.

The bubble sort was defined as a procedure and not a function, so if numbers had been passed by value, a copy of the array would have been passed, and any changes made would not have been kept after the procedure had completed execution.

out of 3

5(ii)

The programmer has used a for loop on line 3 in the procedure bubbleSort. A for loop is a count controlled loop.

State what is meant by the term ‘count controlled loop’.

Mark scheme 5(ii)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

A loop that repeats a fixed / set number of times

Guidance

Examiner’s Comments

Most candidates could accurately define a ‘count controlled loop’ as one that repeated a predefined number of times, although some candidates gave an ambiguous response that was equally applicable to a conditional loop.

out of 1

5(iii)

State the purpose of the variable holdValue in the procedure bubbleSort.

Mark scheme 5(iii)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

  • To temporarily hold a value (for numbers[x])…

  • …while it is being transferred from one position to another…

  • ….in the array numbers

  • To stop values over writing each other

Guidance

Examiner’s Comments

Many candidates found it difficult to explain the purpose of the holdValue variable in context. Where candidates achieved some of the marks, they most frequently identified holdValue as a temporary store that was required to prevent accidental overwriting of data during the swap process. Relatively few were able to accurately describe how the variable allowed the contents of dataArray[x] and dataArray[x+1] to be swapped.

Exemplar 1

[Image redrawn from the original mark scheme by an AI model (Gemma 4 12B). It may contain mistakes.]

A candidate's handwritten answer:

It acts as a temporary variable to hold the value of number [x] while before number is overwritten so the original value is not lost and is instead copied to number[x+1]

This exemplar very clearly states exactly how and why the variable holdValue is required.

out of 3

5(iv)

The procedure bubbleSort will only partially sort the array numbers into order.

Describe what the programmer would need to add to the algorithm to enable it to fully sort the numbers into order.

Mark scheme 5(iv)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

  • Add a (second outer) loop

  • That will repeat for each pass / repeat until the flag is set to true at the end of a pass

Guidance

Examiner’s Comments

Many candidates found it challenging to apply knowledge of a bubble sort to the code given. While a pleasing number identified the need to have an outer loop, there were far fewer

who were able to expand on this to explain that this was required to repeat the process for the requi red number of passes, or until no swaps had occurred during a pass.

out of 2

Question 6

4 marks

6

Lucas writes a program that makes use of a circular queue. The queue stores the data entered into the program. An array is used to represent the queue.

The program needs two pointers to access and manipulate the data in the queue.

State the purpose of the two pointers and give an appropriate identifier for each.

Pointer 1 purpose

Pointer 1 identifier

Pointer 2 purpose

Pointer 2 identifier

Mark scheme 6

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark for the purpose and 1 mark for matching appropriate name (4 marks total), e.g:

  • Pointer to the first element in the queue

  • firstElement / any other meaningful name

  • Pointer to the last element in the queue / Pointer to the first free element in the queue

  • lastElement / any other meaningful name

Guidance

Must cover purpose and name for 2 marks for each pointer.

out of 4

Question 7

16 marks

7(a)

Hugh has written a recursive function called thisFunction() using pseudocode.

01 function thisFunction(theArray, num1, num2, num3)
02  result = num1 + ((num2 - num1) DIV 2)
03  if num2 < num1 then
04    return -1
05  else
06    if theArray[result] < num3 then
07      return thisFunction(theArray, result + 1, num2, num3)
08    elseif theArray[result] > num3 then
09      return thisFunction(theArray, num1, result - 1, num3)
10    else
11      return result
12    endif
13  endif
14 endfunction

The function DIV calculates integer division, e.g. 5 DIV 3 = 1

theArray has the following data:

Index:01234567
Data:510152025303540

Trace the algorithm, and give the final return value, when it is called with the following statement:

thisFunction(theArray, 0, 7, 35)

You may choose to use the table below to give your answer.

Function callnum1num2num3result
thisFunction(theArray,0,7,35)

Final return value ……

Mark scheme 7(a)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark per bullet

  • Calculation of result to 3

  • Call with thisFunction(theArray, num1=4,

num2=7, num3=35)

  • Result = 5

  • call with

thisFunction(theArray,num1=6,num2=7,num3
=35)

  • (Result = 6) return of value 6

Function call num1 num2 num3 result

thisFunction

0 7 35 3

(theArray,0,7,35)
thisFunction

4 7 35 5

(theArray,4,7,35)
thisFunction

6 7 35 6

(thisArray,6,7,35)

Function call

num1

num2

num3

result

thisFunction
(theArray,0,7,35)

thisFunction
(theArray,4,7,35)

thisFunction
(thisArray,6,7,35)

Guidance

7

35

3

7

35

5

7

35

6

out of 5

7(b)

State the name of the standard algorithm thisFunction() performs.

Mark scheme 7(b)

Binary search

7(c)

Hugh could have written thisFunction() using iteration instead of recursion.

Compare two differences between recursion and iteration.

1

2

Mark scheme 7(c)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark per bullet to max 4, e.g.

  • Recursion uses more memory…

  • …iteration uses less memory

  • Recursion declares new variables /variables are put onto the stack each time…

  • …iteration reuses the same variables

  • Recursive can run out of memory/stack space…

  • …while iteration cannot run out of memory

  • Recursion can express a problem more elegantly / in fewer lines of code…

  • …while iteration can take more lines of code / be harder to understand

  • Recursion will be self-referential / will call itself…

  • … whereas iteration does not

out of 4

7(d)

The recursive function thisFunction() is printed again here for your reference.

01 function thisFunction(theArray, num1, num2, num3)
02  result = num1 + ((num2 - num1) DIV 2)
03  if num2 < num1 then
04    return -1
05  else
06    if theArray[result] < num3 then
07      return thisFunction(theArray, result + 1, num2, num3)
08    elseif theArray[result] > num3 then
09      return thisFunction(theArray, num1, result - 1, num3)
10    else
11      return result
12    endif
13  endif
14 endfunction

Rewrite the function thisFunction() so that it uses iteration instead of recursion.

You should write your answer using pseudocode or program code.

Mark scheme 7(d)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark per bullet to max 6

  • Retains function call

  • Uses a loop

  • …that will loop until all elements inspected or value found

  • Updates num1 appropriately

  • Updates num2 appropriately

  • Returns -1 in the correct place if the value has not been found

  • Returns the result in the correct place if the value has been found

e.g.

function thisFunction(theArray, num1, num2, num3)

while (true)
  result = num1 + ((num2 - num1) DIV 2)
  if num2 < num1 then
   return -1
  else
   if theArray[result] < num3 then
    num1 = result + 1
   elseif theArray[result] > num3 then
    num2 = result - 1
   else
    return result
   endif
  endif
endwhile
endfunction
out of 6

Question 8

3 marks

8

The following pseudocode procedure performs an insertion sort on the array parameter.

01 procedure insertionSort(dataArray:byRef)
02  for i = 1 to dataArray.Length - 1
03    temp = dataArray[i]
04    tempPos = i – 1
05    exit = false
06    while tempPos >= 0 and exit == false
07      if dataArray[tempPos] < temp then
08        dataArray[tempPos + 1] = dataArray[tempPos]
09        tempPos = tempPos - 1
10      else
11        exit = true
12      endif
13    endwhile
14    dataArray[tempPos + 1] = temp
15  next i
16 endprocedure

State whether the procedure insertionSort sorts the data into ascending or descending order and explain your choice.

Mark scheme 8

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark pet bullet to max 3

  • Descending order

  • Line 07 (dataArray[tempos]<temp) has the comparison…

  • …that checks if current position is less than item to insert and…

  • …breaks out of loop when current position is less than or equal to item to insert

out of 3

Question 9

32 marks

9(a)

A printer buffer is a storage area that holds the data, known as jobs, that are to be printed by a printer.

A simulation of the printer buffer uses a queue data structure to store jobs that are waiting to be printed. The queue is not circular.

The printer buffer is represented as a zero-indexed 1D array with the identifier buffer.

Fig. 2 shows the current contents of the queue buffer and its pointers.

[Diagram redrawn from the original paper by an AI model (Gemma 4 12B). It may contain mistakes.]

IndexValue
6
5
4
3job-127
2job-126
1job-125
0job-124

queueHead = 0 queueTail = 3

Fig. 2

State the purpose of the pointers queueHead and queueTail.

queueHead

queueTail
Mark scheme 9(a)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark per pointer

  • queueHead: Point to the first element in the queue / next element to remove

  • queueTail: Point to the last element in the queue

out of 2

9(b)

The function dequeue outputs and removes the next data item in the queue.

The procedure enqueue adds the job passed as a parameter to the queue.

Show the final contents of the queue and pointer values after the following instructions have been run on the queue buffer shown in Fig. 2.

dequeue()

dequeue()

enqueue(job-128)

dequeue()

enqueue(job-129)

[Diagram redrawn from the original paper by an AI model (Gemma 4 12B). It may contain mistakes.]

IndexValue
6
5
4
3
2
1
0

queueHead [ ] queueTail [ ]

Mark scheme 9(b)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark per bullet up to max 5

  • first 3 jobs removed

  • 128 and 129 added in positions 4 and 5 respectively

  • no additional jobs

  • queueHead being 3 (FT errors)

  • queueTail being 5 (FT errors)

[Image redrawn from the original mark scheme by an AI model (Gemma 4 12B). It may contain mistakes.]

IndexValue
6
5job-127
4job-128
3job-127
2
1
0

queueHead = 3 queueTail = 5

Guidance

The underlying
implementation of the queue has not been specified, so allow alternative valid answers. e.g.
queueHead = 0
queueTail = 2
Location 2: 129
Location 1: 128
Location 0: 127

out of 5

9(c)

The array, buffer and pointer values are declared with global scope.

9(c)(i)

The function dequeue returns null if the array is empty, and the contents of the next element if not empty. The queue is not circular.

Write an algorithm, using pseudocode or program code, for the function dequeue().

Mark scheme 9(c)(i)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark per bullet to max 5

  • Function declaration

  • Checking if queue is empty

  • …returning null

  • (Otherwise) incrementing queueHead

  • …returning buffer[queueHead-1]

e.g.

function dequeue()
  if queueHead > queueTail then
   return null
  else
   queueHead = queueHead + 1
   return buffer[queueHead-1]
  endif
endfunction

Guidance

Note: Accept alternative valid underlying
implementation answers e.g. Shifting all elements in queue forward.

out of 5

9(c)(ii)

The function enqueue returns -1 if there is no space at the end of the queue to add data, and returns 1 if the parameter was added to buffer. The array buffer contains a maximum of 100 elements.

Write an algorithm, using pseudocode or program code, for the function enqueue().

Mark scheme 9(c)(ii)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark per bullet to max 6

  • Function declaration taking parameter

  • Checking if queue is full

  • …returning -1

  • (Otherwise) incrementing queueTail

  • Adding newJob to buffer(queueTail)

  • Returning 1

e.g.

function enqueue(newJob)
  if queueTail == 99 then
   return -1
  else
   queueTail = queueTail + 1
   buffer[queueTail] = newJob
   return 1
  endif
endfunction
out of 6

9(c)(iii)

In the main program of the simulation the user is asked whether they want to add an item to the queue or remove an item.

If they choose to add an item they have to input the job name, and the function enqueue is called.

If they choose to remove an item, the function dequeue is called and the job name is output.

Appropriate messages are output if either action cannot be run because the queue is either empty or full.

Write, using pseudocode or program code, an algorithm for the main program of the simulation.

Mark scheme 9(c)(iii)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark per bullet to max 8

  • Inputting user choice

  • If enqueue chosen input job name

  • …call enqueue with input value as parameter

  • …check if return value is -1 and output full

  • …otherwise output message that item is added

  • If dequeue chosen

  • …call dequeue and save returned value

  • …output returned value (jobname) if not null

  • …or output queue is empty

e.g.

main()
  choice = input("Add or remove?")
  if choice == "ADD" then
   jobname = input("Enter job name")
   returnValue = enqueue(jobname)
   if returnValue == -1 then
    print("Queue full")
   else
    print("Job added")
   endif
  else
   returnValue = dequeue()
   if returnValue == null then
    print("Queue empty")
   else
    output returnValue
   endif
  endif
endmain

Guidance

Allow equivalent checks / logic

out of 8

9(d)

The queue is changed to make it a circular queue.

Describe how the functions enqueue and dequeue will need to be changed to allow buffer to work as a circular queue.

Mark scheme 9(d)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark per bullet to 3

  • Check if either head or tail are incremented to above 99

  • … set to be 0 instead

  • When checking if array is full check if (queueTail == queueHead – 1) OR (queueTail==99 AND queueHead==0)

Guidance

Credit equivalent modulo arithmetic solution

out of 3

9(e)

Some print jobs can have different priorities. The higher the priority the sooner the job needs to be printed.

Describe how the program could be changed to deal with different priorities.

Mark scheme 9(e)

Tick each point your answer makes. Your mark is worked out from your ticks, and you can change it.

1 mark per bullet to max 3, e.g.

  • Use a different structure e.g. a linked list

  • …items can be added at different points in the linked list depending on priority

  • …by changing the pointers to items needing priority

  • Have different queues for different priorities

  • …add the job to the queue relevant to its priority

  • …print all the jobs in the highest priority queue first

Guidance

Allow other suitable descriptions that show how the program could be amended.

out of 3

Question 10

3 marks

10(a)

Given the following procedure:

procedure maths(number)
   a = (number DIV 10) * 10
   b = a + 10
   if (number – a) >= (b – number) then
     print(b)
   else
     print(a)
   endif
endprocedure

State the value printed by the procedure maths if number=10

Mark scheme 10(a)

  • 10

1

A03.2 (1)

10(b)

State the value printed by the procedure maths if number=27

Mark scheme 10(b)

  • 30

1

A03.2 (1)

10(c)

State the value printed by the procedure maths if number=14

END OF QUESTION PAPER

Mark scheme 10(c)

  • 10

1

A03.2 (1)