Download A23cmp Assessment 4

Computer Science (A Level)
A23cmp Assessment #4
Duration: 60 minutes
Student Number:
Teacher:
INSTRUCTIONS
• Use black ink. HB pencil may be used for graphs and diagrams only.
• Answer all the questions.
• Read each question carefully. Make sure you know what you have to do before starting your answer.
• Where space is provided below the question, please write your answer there.
• You may use additional paper, or a specific Answer sheet if one is provided, but you must clearly show
your candidate number, centre number and question number(s).
INFORMATION FOR CANDIDATES
• The total number of marks for this paper is 60.
• The number of marks is given in brackets [ ] at the end of each question or part question.
• Quality of extended repsonses will be assessed in questions marked was an asterisk (*).
Question
1
2
3
4
5
6
7
8
9
10
11
12
Total
Mark
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/3
/2
/3
/6
/9
/2
/11
/2
/3
/5
/3
/11
/60
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1. Operating systems make use of device drivers.
Define what is meant by the term ‘device driver’, giving one example of a device driver that a home
user would need.
Definition
Example
[3]
2. Julie is a university student. She is considering buying a laptop to help with her studies both at
home and university. Her friend has told her she will need to choose an operating system to run on
her laptop.
The operating system Julie is considering makes use of paging to manage the laptop’s memory.
Explain one benefit of using paging for this purpose.
[2]
3. A cinema offers discounted tickets, but only under one of the following conditions:
•
•
Customer is under 18 and has a student card.
Customer is over 60 and has ID which proves this.
Let:
A be Customer is under 18
B be Customer has a student card
C be Customer is over 60
D be Customer has ID
Q be Discount ticket issued
Complete the Boolean expression below:
Q≡
………………………………………………………………………………………………… [3]
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4(a). Show how the denary value −9.125 can be represented in normalised floating point format,
using 8 bits for the mantissa and 4 bits for the exponent, both in two’s complement.
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[4]
(b). Describe a mask that could be applied to an 8-bit number to ensure that:
•
•
the most significant bit is always set to 1
all other bits remain unchanged.
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[2]
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5*. A program is needed to plan the layout of a garden.
The program will allow the user to create an image of the garden, for example:
The programmer is designing the program to make use of caching and re-useable components.
Explain and evaluate the use of caching and re-useable components in the design of the garden
program.
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[9]
6 Staff working in a factory can report an IT problem to a help desk where details are recorded in a
database. An engineer can then be allocated to resolve the problem.
Two tables in the database are:
Write an SQL statement to output the Date and Location for all problems allocated to the engineer
with Surname Wong and Initial K. [2]
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[2]
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7(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.
Fig. 2
(a) 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)
[5]
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(b) 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().
[6]
8. 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
(a) State the value printed by the procedure maths if number=10
………………….. [1]
(b) State the purpose of the procedure maths.
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[1]
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9(a). Bubble sorts make use of two different loops when sorting items into order.
Describe the two loops used and their purpose.
1
2
[2]
(b). Poppy would like to use a bubble sort to sort 250 000 numbers into order from lowest to highest.
Currently the first five numbers before they have been sorted are:
195 584
167 147
158 187
160 125
184 236
Currently the last five numbers before they have been sorted are:
1058
19 558
1915
20 215
15
State the number of comparisons that will need to be made in the first pass of the bubble sort.
[1]
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10. Albert runs a competition each week in his local village hall. So that Albert can contact the winner
he would like a program for the winner to enter their telephone number which is then checked and
written into a text file.
The rules for Albert’s program are as follows:
1.
2.
3.
4.
5.
The telephone number is entered. This is checked to ensure that the first digit is a 0
If the first digit is not a 0 then a message saying “Needs To Start With 0” is printed
If the first digit is a 0 then the telephone number is passed into a pre-existing function called
checkLength as a parameter. This will return true if the length of the telephone number is long
enough
If the telephone number is long enough then it is written into a text file called "winner.txt"
If the telephone number is not long enough then a message saying “Not Long Enough” is
printed.
Complete the procedure competitionWinner so that it meets the rules of Albert’s program.
You should write your procedure using pseudocode.
procedure competitionWinner()
endprocedure
[5]
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11. Oscar owns a taxi company. He would like a program to handle taxi bookings from customers.
Some of Oscar’s customers are rated as gold. Customers who are rated as gold are given
priority when they make a taxi booking. Some customers rated as gold are shown here.
Arshad
Betty
Dave Freddie Harry
Jimmy Kanwal Lynn
Siad Tommy Will
When a customer makes a booking, Oscar will make use of a binary search to check if they are gold
rated.
Oscar would like to know if ‘Tommy’ is gold rated.
State the three values that will be set as the midpoints and then checked against ‘Tommy’ on each
iteration of the binary search.
Show your working here.
Midpoint 1
Midpoint 2
Midpoint 3
[3]
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12(a). A supermarket uses an object-oriented approach to organise items that it offers for sale. Part of
the class definition for the ItemForSale class is shown below.
class ItemForSale
public itemName
public price
public discount
…
endclass
The supermarket has previously had issues with discounts being set as values above 50.
Explain how encapsulation could be applied to the ItemForSale class to stop this problem from
occurring.
You are not expected to write any code in your answer to this question.
[3]
(b). The discount attribute represents a percentage discount on the price. The discount can be
between 0 and 50 (inclusive). All new items for sale initially have a discount value of 0.
(i)
Write the constructor method for the ItemForSale class.
[4]
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(ii)
Write a line of code to create an object of type ItemForSale called mushypeas
that has a name of “mushy peas” and a price of £0.89
[1]
(iii)
Write the calculatePrice() method, which applies the percentage discount to the
price and returns the new value.
[3]
END OF QUESTION PAPER
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Mark scheme
Question
Answer/Indicative content


1
Software/program
…that allows the operating
system to communicate with
hardware
Examples:




Printer driver
Webcam driver
Sound card driver
Graphics card driver etc.
Total
Marks
Guidance
3
AO1.1
(1)
AO2.1
(2)
Max two for description, Max one for
example
3
1 mark per bullet up to a maximum of 2
marks, e.g:


2


Programs/data can be held in
non-contiguous memory
locations (using virtual
addressing)…
…making it easier to make best
use of remaining storage/ to
avoid having to move content
around to fit in new programs.
It allows pages to be transferred
to and from secondary storage
(i.e. virtual memory).
As random access there is no
performance drop vs sequential
storage
2
AO1.2
(2)
Accept (C∧D) ∨ (A∧B)
Q = (A∧B) ∨ (C∧D)
Accept (B∧A) instead of (A∧B)
3
3
1 mark for (A∧B)
(AO1.2)
1 mark for (C∧D)
Accept (D∧C) instead of (C∧D)
Accept alternative notations (e.g. +/.
OR / AND)
Accept AB as (A.B) and CD as (C.D)
1 mark for the ∨ joining the two parts.
Accept answers without brackets
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Examiner’s Comments
In general, most candidates achieved
all of the available marks in these
questions.
Total
4
a
b
3




10110.111 in fixed point
Gives mantissa of 10110111
exponent is 4 = 0100
Forming final answer of
10110111 0100


1000 0000
OR
4
AO1.2
2
AO2.2
Total
9
5 LOR check inventory
6
Total
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2
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1 mark per pointer

7
a

queueHead: Point to the first
element in the queue / next
element to remove
queueTail: Point to the last
element in the queue
2
AO1.2
(2)
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)
b
5
AO2.1
(2)
AO2.2
(3)
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
1 mark per bullet to max 5





c
i
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
1 mark per bullet to max 6
ii


Function declaration taking
parameter
Checking if queue is full
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5
AO2.2
(2)
AO3.3
(3)
Note: Accept alternative valid
underlying implementation answers
e.g. Shifting all elements in queue
forward.
6
AO2.2
(3)
AO3.3
(3)
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

…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
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







iii
e.g.
main()
choice = input("Add or remove?")
8
AO2.2
(2)
AO3.3
(6)
if choice == "ADD" then
jobname = input("Enter job
name")
returnValue = enqueue(jobname)
if returnValue == -1 then
print("Queue full")
Allow equivalent checks / logic
else
print("Job added")
endif
else
returnValue = dequeue()
if returnValue == null then
print("Queue empty")
else
output returnValue
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endif
endif
endmain
1 mark per bullet to 3

d


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)
3
AO2.1
(1)
AO2.2
(2)
Credit equivalent modulo arithmetic
solution
1 mark per bullet to max 3, e.g.


e




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
Total
3
AO2.1
(2)
AO2.1
(1)
Allow other suitable descriptions that
show how the program could be
amended.
32
1
8
a

A03.2
(1)

b
10
To round the number to the
nearest 10
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1
A02.1
(1)
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1 mark per bullet up to a maximum of 4
marks:

9
a
b


The inner loop will compare all of
the adjacent items in a single
pass
The outer loop will repeat the
process of checking adjacent
items until all passes are
complete / the items are
sorted/no swaps have been
made in a pass
2
A01.2
(4)
1
A02.2
(1)
249,999
Total
5
1 mark per bullet up to a maximum of 5
marks, e.g.:



10



Allow other valid interpretations
e.g. conditional while loop … used to
compare against swap flag after each
pass; counter controlled for loop …
used to check adjacent items on each
pass
Suitable logic for inputting the
telephone number
Suitable logic for ensuring the
telephone number starts with a 0
Suitable logic for passing the
telephone number into the
function checkLength
If true, suitable logic for
opening and closing
winner.txt
…suitable logic for writing the
telephone number to
winner.txt
Suitable logic for printing “Needs
To Start With 0” and "Not Long
Enough"
Total
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Example Solution:
procedure competitionWinner()
telNum = input("Enter Telephone
Number")
if telNum[0] == "0" then
length = checkLength(telNum)
5
AO3.1
(2)
AO3.2
(3)
if length == true then
myfile = openWrite("winner.txt")
myfile.writeLine(telNum)
myfile.close()
else
print ("Not Long Enough")
endif
else
print (“Needs To Start
With 0”)
endif
endprocedure()
5
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1 mark per bullet up to a maximum of 3
marks:
11
i



5 (Jimmy)
8 (Siad)
9 (Tommy)

discount attribute made
private
Set method created
…that restricts value to
maximum 50%


12 a


b
i


3
A02.1
(3)
Constructor method definition
(.e.g new)
itemname, price passed in as
parameters (must use different
identifier names to the ones in
the question)
…and assigned to attributes
discount attribute assigned to
0.
3
AO2.2
4
AO3.2
Example answer
public procedure
new(nItemName, nPrice)
itemname = nItemname
price = nPrice
discount = 0
endprocedure
Look out for alternative notation
e.g.
this.itemname = itemName
Example answers
mushypeas=new
ItemForSale("mushy peas",
0.89)

ii
creating object with identifier
mushypeas = and type
ItemForSale with
parameters passed in as needed
1
AO3.2
ItemForSale mushypeas =
ItemForSale(“mushy
peas”,0.89);
mushypeas=ItemForSale((“mushy
peas”,0.89);
Do not penalise for use of self
parameter as used by languages such
as Python.
Must be correct case and spelling

iii


method definition for
calculatePrice()
applies percentage discount
…returns calculated value
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Percentage discount must be applied
correctly.
3
AO3.2
Example answer
function calculatePrice()
newPrice = price –
(price * discount/100)
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return newPrice
end function
Total
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