A- Level Computer Science 9608

Transcription

1 A- Level Computer Science to 207 Past Papers & Mark Schemes Compiled by: M Mushtaq Hussain

2 2 Cambridge International Examinations Cambridge International Advanced Level * * COMPUTER SCIENCE 9608/32 Paper 3 Advanced Theory May/June 205 hour 30 minutes Candidates answer on the Question Paper. No Additional Materials are required. No calculators allowed. READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. No marks will be awarded for using brand names of software packages or hardware. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. The maximum number of marks is 75. This document consists of 2 printed pages. DC (FD) 0069 UCLES 205 [Turn over

3 2 3 The following syntax diagrams, for a particular programming language, show the syntax of: an assignment statement a variable a letter an operator Assignment statement Variable = Variable Operator Variable ; Variable Letter Letter Letter Letter a Operator + b c d (a) The following assignment statements are invalid. Give the reason in each case. (i) a = b + c Reason......[] (ii) a = b 2; Reason......[] (iii) a = dd * cce; Reason......[] UCLES /32/M/J/5

4 3 4 (b) Write the Backus-Naur Form (BNF) for the syntax diagrams shown on the opposite page. <assignmentstatement> ::=... <variable> ::=... <letter> ::=... <operator> ::=...[6] (c) Rewrite the BNF rule for a variable so that it can be any number of letters. <variable> ::=...[2] (d) Programmers working for a software development company use both interpreters and compilers. (i) The programmers prefer to debug their programs using an interpreter. Give one possible reason why....[] (ii) The company sells compiled versions of its programs. Give a reason why this helps to protect the security of the source code....[] UCLES /32/M/J/5 [Turn over

5 4 5 2 The incomplete table below shows descriptions and terms relating to malware. (a) Complete the table with appropriate descriptions and terms. Description Term A Unsolicited s containing advertising material sent to a distribution list.... B A standalone piece of malicious software that can reproduce itself automatically.... C Pharming D Phishing [4] (b) For one of the terms, describe: a problem that might arise for a user a possible solution to the problem Choose between the terms: A / B (circle your choice) Problem Solution......[2] UCLES /32/M/J/5

6 5 6 (c) Explain the following terms: Encryption Public key [2] (d) A user downloads software from the Internet. (i) State what should be part of the download to provide proof that the software is authentic....[] (ii) Describe the process for ensuring that the software is both authentic and has not been altered....[4] UCLES /32/M/J/5 [Turn over

7 6 7 3 (a) A particular programming language allows the programmer to define their own data types. ThisDate is an example of a user-defined structured data type. TYPE ThisDate DECLARE ThisDay : (, 2, 3, 4, 5, 6, 7, 8, 9, 0,, 2, 3, 4, 5, 6, 7, 8, 9, 20, 2, 22, 23, 24, 25, 26, 27, 28, 29, 30, 3) DECLARE ThisMonth DECLARE ThisYear : INTEGER ENDTYPE A variable of this new type is declared as follows: DECLARE DateOfBirth : ThisDate : (Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec) (i) Name the non-composite data type used in the ThisDay and ThisMonth declarations....[] (ii) Name the data type of ThisDate....[] (iii) The month value of DateOfBirth needs to be assigned to the variable MyMonthOfBirth. Write the required statement....[] UCLES /32/M/J/5

8 7 8 (b) Annual rainfall data from a number of locations are to be processed in a program. The following data are to be stored: location name height above sea level (to the nearest metre) total rainfall for each month of the year (centimetres to decimal place) A user-defined, composite data type is needed. The programmer chooses LocationRainfall as the name of this data type. A variable of this type can be used to store all the data for one particular location. (i) Write the definition for the data type LocationRainfall....[5] (ii) The programmer decides to store all the data in a file. Initially, data from 27 locations will be stored. More rainfall locations will be added over time and will never exceed 00. The programmer has to choose between two types of file organisation. The two types are serial and sequential. Give two reasons for choosing serial file organisation....[2] UCLES /32/M/J/5 [Turn over

9 8 9 4 (a) (i) Complete the truth table for this logic circuit: A X B A B Working space X [] (ii) Complete the truth table for this logic circuit: A X B A B Working space X [] UCLES /32/M/J/5

10 9 0 (b) A student decides to write an equation for X to represent the full behaviour of each logic circuit. (i) Write the Boolean expression that will complete the required equation for X for each circuit: Circuit : X =... Circuit 2: X =...[2] (ii) Write the De Morgan s Law which is shown by your answers to part (a) and part (b)(i)....[] (c) Write the Boolean algebraic expression corresponding to the following logic circuit: A B X...[3] (d) Using De Morgan s laws and Boolean algebra, simplify your answer to part (c). Show all your working [3] UCLES /32/M/J/5 [Turn over

11 0 5 A gardener grows vegetables in a greenhouse. For the vegetables to grow well, the temperature needs to always be within a particular range. The gardener is not sure about the actual temperatures in the greenhouse during the growing season. The gardener installs some equipment. This records the temperature every hour during the growing season. (a) Name the type of system described....[] (b) Identify three items of hardware that would be needed to acquire and record the temperature data. Justify your choice for each. Item... Justification Item 2... Justification Item 3... Justification......[6] (c) The equipment records temperatures in the greenhouse. It does this for seven locations. Each recording is stored as two successive bytes. The format is shown below: Greenhouse location Temperature reading Byte Byte 2 The location is indicated by the setting of one of the seven bits in byte. For example, location 4 is indicated by setting bit 4. Bit 0 of byte acts as a flag: the initial value is zero when the reading has been processed it is set to Byte 2 contains the temperature reading (two s complement integer). UCLES /32/M/J/5

12 2 (i) Interpret the data in byte shown below: Byte Byte 2...[2] (ii) The system receives a temperature reading of 5 degrees from sensor 6. Complete the boxes below to show the two bytes for this recording. The reading has not yet been processed Byte Byte 2 (d) (i) The accumulator is loaded with the value of byte from location 06. Write the assembly language instruction to check whether the reading in byte 2 came from location 4. LDD 06 // data loaded from address 06...[4] [2] (ii) Write the assembly language instruction to set the flag (bit 0) of the byte contained in the accumulator to....[2] UCLES /32/M/J/5 [Turn over

13 2 3 6 (a) Four descriptions and three protocols are shown below. Draw a line to connect each description to the appropriate protocol. Description Protocol used client downloads an from an server HTTP is transferred from one server to another server POP3 client sends to server SMTP browser sends a request for a web page to a web server (b) Downloading a file can use the client-server model. Alternatively, a file can be downloaded using the BitTorrent protocol. Name the model used....[] (c) For the BitTorrent protocol, explain the function of each of the following: (i) Tracker......[2] (ii) Seed......[2] (iii) Swarm......[2] [4] To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge International Examinations Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at after the live examination series. UCLES /32/M/J/5

14 4 CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Level MARK SCHEME for the May/June 205 series 9608 COMPUTER SCIENCE 9608/32 Paper 3 (Written paper), maximum raw mark 75 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 205 series for most Cambridge IGCSE, Cambridge International A and AS Level components and some Cambridge O Level components. IGCSE is the registered trademark of Cambridge International Examinations.

15 Page 2 Mark Scheme Syllabus Paper Cambridge International A Level May/June (a) (i) ; missing 5 (ii) 2 is not a variable (iii) e is not a valid letter (b) <assignment statement> ::= <variable> = <variable><operator><variable>; <variable> ::= <letter> <letter><letter> <letter><letter><letter> <letter> ::= a b c d 2 2 <operator> :: =+ - * (c) <letter> <letter><variable> // <letter> <variable><letter> 2 (d) (i) debugging is faster / easier // can debug incomplete code // better diagnostics (ii) compiler produces executable version not readable / no need for source code // difficult to reverse-engineer Total: 3 2 (a) Spam Worm Pharming redirect website to fake website // domain name server compromised // proxy server compromised Phishing through attempt to obtain somebody s confidential data / install malware (b) Spam user s inbox is filled by large amount of unwanted user / server employs filtering software that can divert / delete spam Worm could corrupt user s computer // delete data // consume bandwidth run anti-virus software in the background // not connect to the Internet // keep OS up-to-date or Cambridge International Examinations 205

16 6 Page 3 Mark Scheme Syllabus Paper Cambridge International A Level May/June (c) encryption: process of turning plain text into cipher text public key: key widely available that can be used to encrypt message that only owner of private key can decrypt // can be used to decrypt a message thereby confirming originator of message (d) (i) digital signature (ii) software is put through hashing algorithm hash total is encrypted with private key (digital signature) software + encrypted hash / digital signature are sent receiver is in possession of sender s public key the received hash total / digital signature is decrypted with public key (SH) the receiver hashes received software (RH) If SH matches RH then software is authentic and has not been altered Any four points mark each Total: 3 3 (a) (i) enumerated (ii) record (iii) MyMonthOfBirth DateOfBirth.ThisMonth (b) (i) TYPE LocationRainfall DECLARE LocationName : STRING DECLARE LocationHeight : INTEGER DECLARE TotalMonthlyRainfall : ARRAY[..2] OF REAL ENDTYPE + (ii) no need to re-sort data every time new data is added only a small file so searching will require little processing new records can easily be appended [max 2] Total: 0 4 (a) (i) Circuit A B X Cambridge International Examinations 205

17 7 Page 4 Mark Scheme Syllabus Paper Cambridge International A Level May/June (ii) Circuit 2 A B X (b) (i) circuit : A. B circuit 2: A + B (ii) A. B A + B (c) (d) ( A + B). B Mark as follows: ( A+ B). B bar over whole expression ( A + B). B = ( A + B) + B = ( A + B) + B = A + ( B + B) = A + = allow f.t. from (c) [max 3] Total: 5 (a) Monitoring system (b) temperature sensor transmits measured temperature analogue to digital converter converts analogue signal from sensor to digital value that can be stored storage device // data logger for recording readings from sensor transmission hardware to transfer data from sensor to storage device processor to process incoming data [max 6] Cambridge International Examinations 205

18 8 Page 5 Mark Scheme Syllabus Paper Cambridge International A Level May/June (c) (i) temperature reading in location 5 has been processed (ii) mark per byte (d) (i) AND #B // AND #&0 // AND #6 mark for AND, mark for address mode, mark for mask, mark for indication of numbering system (ii) OR #B // OR #&0 // OR # mark for OR, mark for mask Total: 7 6 (a) Description Protocol used client downloads an from an server is transferred from one server to another server HTTP POP3 mark for correct arrow from each description client sends to server SMTP browser sends a request for a web page to a web server (b) peer-to-peer (c) (i) (ii) (iii) Tracker: central server that: stores details of other computers that have all / part of file to be downloaded // has data on those peers downloading and uploading file // shares IP addresses with other clients in swarm allowing them to connect Seed: peer computer that has 00% of file // is uploading downloaded content Swarm: all the connected peer computers that have all or part of the file to be downloaded / uploaded // share a torrent Total: Cambridge International Examinations 205

19 9 Cambridge International Examinations Cambridge International Advanced Level * * COMPUTER SCIENCE 9608/33 Paper 3 Advanced Theory May/June 205 hour 30 minutes Candidates answer on the Question Paper. No Additional Materials are required. No calculators allowed. READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. No marks will be awarded for using brand names of software packages or hardware. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. The maximum number of marks is 75. This document consists of 4 printed pages and 2 blank pages. DC (ST/SW) 95542/2 UCLES 205 [Turn over

20 2 20 The following syntax diagrams, for a particular programming language, show the syntax of: an assignment statement a variable a number a letter a digit an operator Assignment statement Variable := Variable Operator Number Variable Letter Number Number Digit Letter A B C Digit Operator + / UCLES /33/M/J/5

21 3 2 (a) The following assignment statements are invalid. Give a reason in each case. (i) A2 = B Reason......[] (ii) B3 := B3 203 Reason......[] (iii) A244 := A3 * B Reason......[] (b) Complete the Backus-Naur Form (BNF) for the syntax diagrams shown on the opposite page. <letter> has been done for you. <assignmentstatement> ::=... <variable> ::=... <number> ::=... <letter> ::= A B C <digit> ::=... <operator> ::=... [6] UCLES /33/M/J/5 [Turn over

22 4 22 (c) A company develops software. It provides virtual machines for its software developers. The company has a large number of clients who use a wide range of hardware and software. (i) Explain the term virtual machine. Ensure that your answer includes the terms hardware and software....[2] (ii) Give one benefit to the company of using virtual machines....[] (iii) Give one drawback to the company of using virtual machines....[] UCLES /33/M/J/5

23 (a) Four descriptions and three types of local area network (LAN) are shown below. Draw a line to connect each description to the type of LAN it applies to. Description Type of LAN Any packet the listening computer receives may be part of a message for itself Bus with terminators at each end Connection provided through an access point Star A process for handling collisions has to be implemented Wireless Listening computer only receives packets that are addressed to itself [4] (b) A user downloads a file using the FTP protocol. Explain the function played by each of the following: (i) Server......[2] (ii) Command......[2] (iii) Anonymous......[2] UCLES /33/M/J/5 [Turn over

24 The incomplete table below shows descriptions and terms relating to malware. (a) Complete the table with appropriate descriptions and terms. Description Term A B Sending s which contain a link to a website that attempts to trick users into giving confidential personal data.... It replicates by inserting itself into another piece of software.... C Worm D Spam [4] (b) Choose term A or term B and describe: a problem that might arise for a user a possible solution to the problem Term... Problem Solution......[2] UCLES /33/M/J/5

25 7 25 (c) Explain the following terms: Cipher text Private key [2] (d) Bill, a manager of a company, sent an with very sensitive information to a work colleague, Alison. However, Bill also accidentally sent it to everybody in the company. Describe the method used that ensured only Alison was able to read the original contents of the [4] UCLES /33/M/J/5 [Turn over

26 (a) A particular programming language allows the programmer to define their own data types. An example of a user-defined data type for an address is: TYPE ThisAddress DECLARE ThisHouseNo : INTEGER DECLARE ThisStreet : STRING DECLARE ThisTown : STRING ENDTYPE A variable of this new type is declared as follows: DECLARE HomeAddress : ThisAddress (i) Write the statement that assigns the house number 34 to HomeAddress....[] (ii) The type definition for ThisAddress is to be changed. Rewrite one line from the definition for each of the following changes. House numbers are in the range from to 0. DECLARE... The possible towns are limited to: Brightown, Arunde and Shoram. DECLARE...[2] UCLES /33/M/J/5

27 9 27 (b) Temperature data from a number of weather stations are to be processed by a program. The following data are to be stored: weather station ID (a unique four-letter code) latitude (to 2 decimal places) average temperature (to the nearest whole number) for each year from 200 to 205 inclusive A programmer designs a composite data type WeatherStation. A variable of this type can be used to store all the data for one particular station. (i) Write the definition for the user-defined data type WeatherStation....[5] (ii) The programmer decides to store all the data in a file. The number of weather stations could grow to reach 20000, but not all stations will be present at first. The programmer decides on random organisation for the file. Describe three steps which show how a new weather station record is added to the file [3] UCLES /33/M/J/5 [Turn over

28 (a) (i) Complete the truth table for this logic circuit: A X B A B Working space X [] (ii) Complete the truth table for this logic circuit: A X B A B Working space X [] UCLES /33/M/J/5

29 29 (b) A student decides to write an equation for X to represent the full behaviour of each logic circuit. (i) Write the Boolean expression that will complete the required equation for X for each circuit: Circuit : X =... Circuit 2: X =...[2] (ii) Write the De Morgan s Law which is shown by your answers to part (a) and part (b)(i)....[] (c) Write the Boolean algebraic expression corresponding to the following logic circuit: A B X...[3] (d) Using De Morgan s laws and Boolean algebra, simplify your answer to part (c). Show all your working [3] UCLES /33/M/J/5 [Turn over

30 A company grows vegetables in a number of large greenhouses. For the vegetables to grow well, the temperature, light level and soil moisture need to always be within certain ranges. The company installs a computerised system to keep these three growing conditions within the best ranges. Sensors are used for collecting data about the temperature, light level, and moisture content of the soil. (a) Name the type of system described....[] (b) Give three items of hardware that would be needed for this system. Justify your choice. Do not include sensors in your answer. Item... Justification Item 2... Justification Item 3... Justification......[6] (c) (i) Describe what is meant by feedback in the above system....[3] (ii) When the system was designed, various parameters for temperature were set. Name one of these parameters....[] UCLES /33/M/J/5

31 3 3 (iii) Explain how this parameter value is used by the feedback system....[2] Question 6 continues on page 4. UCLES /33/M/J/5 [Turn over

32 4 32 Each greenhouse has eight sensors (numbered 8). The byte at address 50 is used to store eight -bit flags. A flag is set to indicate whether its associated sensor reading is waiting to be processed. More than one sensor reading may be waiting to be processed at any particular moment. Data received from the sensors is stored in a block of eight consecutive bytes (addresses ). The data from sensor is at address 20, the data from sensor 2 is at address 202, and so on. Sensor number (d) (i) Interpret the current reading for sensor 2....[2] (ii) The accumulator is loaded with the data from location 50. Write the assembly language instruction to check whether there is a value waiting to be processed for sensor 6. LDD 50 // data loaded from address 50...[3] UCLES /33/M/J/5

33 33 CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Level MARK SCHEME for the May/June 205 series 9608 COMPUTER SCIENCE 9608/33 Paper 3 (Written Paper), maximum raw mark 75 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 205 series for most Cambridge IGCSE, Cambridge International A and AS Level components and some Cambridge O Level components. IGCSE is the registered trademark of Cambridge International Examinations.

34 34 Page 2 Mark Scheme Syllabus Paper Cambridge International A Level May/June (a) (i) Wrong assignment operator (should be := not = ) (ii) 0 is not a digit (iii) B is not a number (b) <assignmentstatement> ::= <variable> := <variable><operator><number> <variable> ::= <letter><number> <number> ::= <digit> <digit><number> <letter> ::= A B C <digit> ::= <operator> ::= + - * / + + (c) (i) Use of software (idea of using) to implement a hardware set-up (idea of implementing / simulating / emulating) (ii) (iii) e.g. no need to acquire client hardware for testing / reduces set-up time for test system / common development system for all developers e.g. software emulation runs slower than real hardware / not possible to emulate some hardware Total: 3 2 (a) Description Type of LAN any packet the listening computer receives may be part of a message for that computer bus with terminators at each end connection provided through an access point star a process for handling collisions has to be implemented listening computer only receives packets that are addressed to this computer wireless mark for correct arrow(s) from each description (b) (i) Server: central computer stores files that are to be downloaded Cambridge International Examinations 205

35 35 Page 3 Mark Scheme Syllabus Paper Cambridge International A Level May/June (ii) (iii) Command: user can send action/instruction (or by example, e.g. change directory) that are carried out on server Anonymous: allows user to access files user does not need to identify themselves to server Total: 0 3 (a) A Phishing B Virus C a standalone piece of software which can reproduce itself automatically D sending unsolicited s to a distribution list (b) (c) e.g. phishing problem: identity fraud / misuse of financial data solution: ignore / don t respond to e.g. virus problem: computer may stop working // lost files solution: running anti-virus software cipher text: encrypted text which is not understandable private key: key only known to owner that can be used to encrypt message to confirm author of message // can be used by owner to decrypt a message thereby ensuring only owner can read message or (d) Manager encrypts using public key of colleague colleague decrypts using his/her private key Total: 2 4 (a) (i) HomeAddress.ThisHouseNo 34 (ii) DECLARE ThisHouseNo:..0 DECLARE ThisTown: [Brightown, Arunde, Shoram] (b) (i) (ii) TYPE WeatherStation DECLARE StationID : STRING DECLARE Latitude : REAL DECLARE Temperature : ARRAY[..5] OF INTEGER ENDTYPE StationID is hashed to produce home location If home location is free insert record Else use overflow method to find free location + Total: Cambridge International Examinations 205

36 36 Page 4 Mark Scheme Syllabus Paper Cambridge International A Level May/June (a) (i) Circuit A B X (ii) Circuit 2 A B X (b) (i) circuit A + B circuit 2 A. B (ii) A+ B A. B (c) (d) ( A. B) + B mark as : ( A. B) + B bar over whole expression ( A. B) + B = ( A. B). B = ( A. B). B = A.( B. B) = A. 0 = 0 allow f.t. from (c) max 3 Total: Cambridge International Examinations 205

37 37 Page 5 Mark Scheme Syllabus Paper Cambridge International A Level May/June (a) Control system (b) Any three different items max 6 marks heater / water pump / blinds pump for altering temperature / watering / light level actuator for fan for distributing air / water pump / blinds motor analogue to digital converter / digital to analogue convertor converts analogue signal from sensor to digital value for processing / converts digital signal to analogue signal for controlling actuator microprocessor executes control software warning device (speaker/buzzer/light) to give warning if conditions out of range / hardware malfunction max 6 (c) (i) output of system (alter temperature / light level / soil moisture) affects input from sensors continuous 3 (ii) min / max / ideal / mean / extreme temperature // sampling rate // tolerance interval (iii) reading from sensor is compared with parameter appropriate action is taken (by example) 2 (d) (i) reading available for processing reading value is 4 (ii) AND #B // AND #&04 // AND #4 mark for AND, mark for address mode, mark for mask, mark for indication of numbering system max 3 Total: 8 Cambridge International Examinations 205

38 38 Cambridge International Examinations Cambridge International Advanced Level * * COMPUTER SCIENCE 9608/43 Paper 4 Further Problem-solving and Programming Skills May/June 205 PRE-RELEASE MATERIAL This material should be given to candidates on receipt by the Centre. READ THESE INSTRUCTIONS FIRST Candidates should use this material in preparation for the examination. Candidates should attempt the practical programming tasks using their chosen high-level, procedural programming language. This document consists of 0 printed pages and 2 blank pages. DC (AC/SW) 95229/3 UCLES 205 [Turn over

39 2 39 This material is intended to be read by teachers and candidates prior to the June 205 examination for 9608 Paper 4. Reminders The syllabus states: there will be questions on the examination paper which do not relate to this pre-release material you must choose a high-level programming language from this list: Visual Basic (Console Mode) Python Pascal / Delphi (Console Mode) The practical skills covered in Paper 2 are a precursor to those required in Paper 4. It is therefore recommended that the high-level programming language chosen for this paper is the same as that for Paper 2. This allows for sufficient expertise to be acquired with the opportunity for extensive practice. Questions on the examination paper may ask the candidate to write: structured English pseudocode program code A program flowchart should be considered as an alternative to pseudocode for the documenting of an algorithm design. Candidates should be confident with: the presentation of an algorithm using either a program flowchart or pseudocode the production of a program flowchart from given pseudocode (or the reverse) UCLES /43/PRE/M/J/5

40 3 40 TASK A linked list Abstract Data Type (ADT) has these associated operations: create linked list add item to linked list remove item from linked list Key focus: Linked lists The linked list ADT consists of a linked list of nodes. Each node consists of data and a pointer to the next node. TASK. Consider the use of a linked list to store names in alphabetical order. The following sequence of operations is carried out: CreateLinkedList AddName("Nabila") AddName("Jack") AddName("Kerrie") AddName("Sara") RemoveName("Kerrie") AddName("Zac") Key focus: Conceptual diagrams of linked lists Add appropriate labels to the diagram to show the final state of the linked list. Use the space on the left as a workspace. Show your final answer in the node shapes on the right: UCLES /43/PRE/M/J/5 [Turn over

41 4 4 TASK.2 The linked list is to be implemented as an array of records, where each record represents a node. The CreateLinkedList operation links all nodes to form the free list and initialises the HeadPointer and FreePointer. Complete the diagram to show the values of all pointers after the CreateLinkedList operation has been carried out. Key focus: Implementation of linked lists using an array of records NameList HeadPointer Name Pointer [] [2] [3] [4] [5] FreePointer [6] [49] [50] Write pseudocode for the CreateLinkedList operation. Write program code from your pseudocode design. UCLES /43/PRE/M/J/5

42 5 42 TASK.3 Complete the diagram to show the values of all pointers after the following operations have been carried out: AddName("Nabila") AddName("Jack") AddName("Kerrie") AddName("Sara") RemoveName("Kerrie") AddName("Zac") NameList HeadPointer Name Pointer [] [2] [3] [4] [5] FreePointer [6] [49] [50] UCLES /43/PRE/M/J/5 [Turn over

43 6 43 TASK.4 Complete the identifier table for the pseudocode given below. Identifier Data type Description Array to store node data Name to be added Pointer to next free node in array Pointer to first node in list Pointer to current node Pointer to previous node Pointer to new node 0 PROCEDURE AddName(NewName) 02 // New name placed in node at head of free list 03 NameList[FreePointer].Name NewName 04 NewNodePointer FreePointer 05 FreePointer NameList[FreePointer].Pointer // initialise current pointer to start of list 08 CurrentPointer HeadPointer 09 0 // check that it is not the special case of adding to empty list IF HeadPointer > 0 2 // loop to locate position of new name 3 // saves current pointer and then updates current pointer 4 WHILE NameList[CurrentPointer].Name < NewName 5 PreviousPointer CurrentPointer 6 CurrentPointer NameList[CurrentPointer].Pointer 7 ENDWHILE 8 ENDIF 9 20 // check to see whether new name is first in linked list 2 // if first item then place item at head of list 22 // if not first item then adjust pointers to place it in correct 23 // position in list 24 IF CurrentPointer = HeadPointer 25 THEN 26 NameList[NewNodePointer].Pointer HeadPointer 27 HeadPointer NewNodePointer 28 ELSE 29 NameList[NewNodePointer].Pointer NameList[PreviousPointer].Pointer 30 NameList[PreviousPointer].Pointer NewNodePointer 3 ENDIF 32 ENDPROCEDURE UCLES /43/PRE/M/J/5

44 7 44 TASK.5 Write program code for the pseudocode given in Task.4. TASK.6 The structured English algorithm for the operation to remove a name from the linked list is as follows: If list is not empty Find the name to be removed If it is the first name in the linked list Adjust the head pointer If it is not the first name in the linked list Adjust pointers to exclude the name to be removed from the list Link released node into free list TASK.6. Write the algorithm, as a procedure in pseudocode, from the structured English given above. TASK.6.2 Write program code from your pseudocode design. TASK.6.3 Test your program code for creating a linked list, adding and removing names, using the data given in Task.3. Suggested extension task Queues, stacks, binary trees and dictionaries can be implemented as linked lists of nodes. Design pseudocode and write program code for these data structures. UCLES /43/PRE/M/J/5 [Turn over

45 8 45 TASK 2 A vehicle hire company has cars and trucks for hire. The unique registration and the engine size (in litres, to the nearest 0. of a litre) are stored for all vehicles. Data stored about cars also include the hire charge per day (in $) and the number of passengers allowed. Data stored about trucks also include the hire charge per hour (in $) and the maximum payload (in kg). Object-oriented software is to be written to process data about vehicles hired, including calculating the hire fee. The superclass (also known as base class or parent class) Vehicle is designed. Two subclasses (also known as derived classes or child classes) have been identified: Car Truck Key focus: Object-oriented programming TASK 2. Complete the inheritance diagram. UCLES /43/PRE/M/J/5

46 9 46 TASK 2.2 Complete the class diagram showing the appropriate properties and methods Constructor() Note: a constructor is a method that creates a new instance of a class and initialises it. TASK 2.3 Write program code for the class definitions. Make use of polymorphism and inheritance where appropriate. TASK 2.4 Write program code to create a new instance of Car. Suggested extension task Write program code to display the properties of the object you created in Task 2.4. UCLES /43/PRE/M/J/5 [Turn over

47 0 47 TASK 3 An intruder detection system is inactive when the power is switched off. The system is activated when the power is switched on. When the system senses an intruder the alarm bell rings. A reset button is pressed to turn the alarm bell off and return the system to the active state. The transition from one state to another is as shown in the state transition table below. Current state Event Next state System inactive Switch power on System active System active Senses intruder Alarm bell rings System active Switch power off System inactive Alarm bell rings Press reset button System active Alarm bell rings Switch power off System inactive Complete the diagram. Key focus: State transition diagrams start UCLES /43/PRE/M/J/5

48 48 Cambridge International Examinations Cambridge International Advanced Level * * COMPUTER SCIENCE 9608/42 Paper 4 Further Problem-solving and Programming Skills May/June 205 PRE-RELEASE MATERIAL This material should be given to candidates on receipt by the Centre. READ THESE INSTRUCTIONS FIRST Candidates should use this material in preparation for the examination. Candidates should attempt the practical programming tasks using their chosen high-level, procedural programming language. This document consists of 0 printed pages and 2 blank pages. DC (RW) 079 UCLES 205 [Turn over

49 2 49 This material is intended to be read by teachers and candidates prior to the June 205 examination for 9608 Paper 4. Reminders The syllabus states: there will be questions on the examination paper which do not relate to this pre-release material you must choose a high-level programming language from this list: Visual Basic (Console Mode) Python Pascal / Delphi (Console Mode) The practical skills covered in Paper 2 are a precursor to those required in Paper 4. It is therefore recommended that the high-level programming language chosen for this paper is the same as that for Paper 2. This allows for sufficient expertise to be acquired with the opportunity for extensive practice. Questions on the examination paper may ask the candidate to write: structured English pseudocode program code A program flowchart should be considered as an alternative to pseudocode for the documenting of an algorithm design. Candidates should be confident with: the presentation of an algorithm using either a program flowchart or pseudocode the production of a program flowchart from given pseudocode (or the reverse) UCLES /42/PRE/M/J/5

50 3 50 TASK A linked list Abstract Data Type (ADT) has these associated operations: create linked list add item to linked list remove item from linked list Key focus: Linked lists The linked list ADT consists of a linked list of nodes. Each node consists of data and a pointer to the next node. TASK. Consider the use of a linked list to store names in alphabetical order. The following sequence of operations is carried out: CreateLinkedList AddName("Nabila") AddName("Jack") AddName("Kerrie") AddName("Sara") RemoveName("Kerrie") AddName("Zac") Key focus: Conceptual diagrams of linked lists Add appropriate labels to the diagram to show the final state of the linked list. Use the space on the left as a workspace. Show your final answer in the node shapes on the right: UCLES /42/PRE/M/J/5 [Turn over

51 4 5 TASK.2 The linked list is to be implemented as an array of records, where each record represents a node. The CreateLinkedList operation links all nodes to form the free list and initialises the HeadPointer and FreePointer. Complete the diagram to show the values of all pointers after the CreateLinkedList operation has been carried out. Key focus: Implementation of linked lists using an array of records NameList HeadPointer Name Pointer [] [2] [3] [4] [5] FreePointer [6] [49] [50] Write pseudocode for the CreateLinkedList operation. Write program code from your pseudocode design. UCLES /42/PRE/M/J/5

52 5 52 TASK.3 Complete the diagram to show the values of all pointers after the following operations have been carried out: AddName("Nabila") AddName("Jack") AddName("Kerrie") AddName("Sara") RemoveName("Kerrie") AddName("Zac") NameList HeadPointer Name Pointer [] [2] [3] [4] [5] FreePointer [6] [49] [50] UCLES /42/PRE/M/J/5 [Turn over

53 6 53 TASK.4 Complete the identifier table for the pseudocode given below. Identifier Data type Description Array to store node data Name to be added Pointer to next free node in array Pointer to first node in list Pointer to current node Pointer to previous node Pointer to new node 0 PROCEDURE AddName(NewName) 02 // New name placed in node at head of free list 03 NameList[FreePointer].Name NewName 04 NewNodePointer FreePointer 05 FreePointer NameList[FreePointer].Pointer // initialise current pointer to start of list 08 CurrentPointer HeadPointer 09 0 // check that it is not the special case of adding to empty list IF HeadPointer > 0 2 // loop to locate position of new name 3 // saves current pointer and then updates current pointer 4 WHILE NameList[CurrentPointer].Name < NewName 5 PreviousPointer CurrentPointer 6 CurrentPointer NameList[CurrentPointer].Pointer 7 ENDWHILE 8 ENDIF 9 20 // check to see whether new name is first in linked list 2 // if first item then place item at head of list 22 // if not first item then adjust pointers to place it in correct 23 // position in list 24 IF CurrentPointer = HeadPointer 25 THEN 26 NameList[NewNodePointer].Pointer HeadPointer 27 HeadPointer NewNodePointer 28 ELSE 29 NameList[NewNodePointer].Pointer NameList[PreviousPointer].Pointer 30 NameList[PreviousPointer].Pointer NewNodePointer 3 ENDIF 32 ENDPROCEDURE UCLES /42/PRE/M/J/5

54 7 54 TASK.5 Write program code for the pseudocode given in Task.4. TASK.6 The structured English algorithm for the operation to remove a name from the linked list is as follows: If list is not empty Find the name to be removed If it is the first name in the linked list Adjust the head pointer If it is not the first name in the linked list Adjust pointers to exclude the name to be removed from the list Link released node into free list TASK.6. Write the algorithm, as a procedure in pseudocode, from the structured English given above. TASK.6.2 Write program code from your pseudocode design. TASK.6.3 Test your program code for creating a linked list, adding and removing names, using the data given in Task.3. Suggested extension task Queues, stacks, binary trees and dictionaries can be implemented as linked lists of nodes. Design pseudocode and write program code for these data structures. UCLES /42/PRE/M/J/5 [Turn over

55 8 55 TASK 2 A vehicle hire company has cars and trucks for hire. The unique registration and the engine size (in litres, to the nearest 0. of a litre) are stored for all vehicles. Data stored about cars also include the hire charge per day (in $) and the number of passengers allowed. Data stored about trucks also include the hire charge per hour (in $) and the maximum payload (in kg). Object-oriented software is to be written to process data about vehicles hired, including calculating the hire fee. The superclass (also known as base class or parent class) Vehicle is designed. Two subclasses (also known as derived classes or child classes) have been identified: Car Truck Key focus: Object-oriented programming TASK 2. Complete the inheritance diagram. UCLES /42/PRE/M/J/5

56 9 56 TASK 2.2 Complete the class diagram showing the appropriate properties and methods Constructor() Note: a constructor is a method that creates a new instance of a class and initialises it. TASK 2.3 Write program code for the class definitions. Make use of polymorphism and inheritance where appropriate. TASK 2.4 Write program code to create a new instance of Car. Suggested extension task Write program code to display the properties of the object you created in Task 2.4. UCLES /42/PRE/M/J/5 [Turn over

57 0 57 TASK 3 An intruder detection system is inactive when the power is switched off. The system is activated when the power is switched on. When the system senses an intruder the alarm bell rings. A reset button is pressed to turn the alarm bell off and return the system to the active state. The transition from one state to another is as shown in the state transition table below. Current state Event Next state System inactive Switch power on System active System active Senses intruder Alarm bell rings System active Switch power off System inactive Alarm bell rings Press reset button System active Alarm bell rings Switch power off System inactive Complete the diagram. Key focus: State transition diagrams start UCLES /42/PRE/M/J/5

58 58 Cambridge International Examinations Cambridge International Advanced Level * * COMPUTER SCIENCE 9608/42 Paper 4 Further Problem-solving and Programming Skills May/June hours Candidates answer on the Question Paper. No Additional Materials are required. No calculators allowed. READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. No marks will be awarded for using brand names of software packages or hardware. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. The maximum number of marks is 75. This document consists of 6 printed pages. DC (SLM) UCLES 205 [Turn over

59 2 59 Throughout the paper you will be asked to write either pseudocode or program code. Complete the statement to indicate which high-level programming language you will use. Programming language... UCLES /42/M/J/5

60 3 60 A turnstile is a gate which is in a locked state. To open it and pass through, a customer inserts a coin into a slot on the turnstile. The turnstile then unlocks and allows the customer to push the turnstile and pass through the gate. After the customer has passed through, the turnstile locks again. If a customer pushes the turnstile while it is in the locked state, it will remain locked until another coin is inserted. The turnstile has two possible states: locked and unlocked. The transition from one state to another is as shown in the table below. Current state Event Next state Locked Insert coin Unlocked Locked Push Locked Unlocked Attempt to insert coin Unlocked Unlocked Pass through Locked Complete the state transition diagram for the turnstile: start... [5] UCLES /42/M/J/5 [Turn over

61 4 6 2 A declarative programming language is used to represent the knowledge base shown below: 0 capital_city(amman). 02 capital_city(beijing). 03 capital_city(brussels). 04 capital_city(cairo). 05 capital_city(london). 06 city_in_country(amman, jordan). 07 city_in_country(shanghai, china). 08 city_in_country(brussels, belgium). 09 city_in_country(london, uk). 0 city_in_country(manchester, uk). country_in_continent(belgium, europe). 2 country_in_continent(china, asia). 3 country_in_continent(uk, europe). 4 city_visited(amman). 5 city_visited(beijing). 6 city_visited(cairo). These clauses have the following meaning: Clause Explanation 0 Amman is a capital city (a) More facts are to be included. 06 Amman is a city in the country of Jordan Belgium is a country in the continent of Europe 4 The travel writer visited Amman The travel writer visited the city of Santiago which is the capital city of Chile, in the continent of South America. Write additional clauses to record this [4] UCLES /42/M/J/5

62 5 62 (b) Using the variable ThisCountry, the goal country_in_continent(thiscountry, europe) returns ThisCountry = belgium, uk Write the result returned by the goal: city_in_country(thiscity, uk) ThisCity = [2] (c) Complete the rule below to list the countries the travel writer has visited. countries_visited(thiscountry) IF [4] UCLES /42/M/J/5 [Turn over

63 A shop gives some customers a discount on goods totalling more than $20. The discounts are: 5% for goods totalling more than $00 5% with a discount card 0% with a discount card and goods totalling more than $00 (a) Complete the decision table. Conditions goods totalling more than $20 goods totalling more than $00 Y Y Y Y N N N N Y Y N N Y Y N N have discount card Y N Y N Y N Y N No discount Actions 5% discount 0% discount [4] (b) Simplify your solution by removing redundancies. Conditions goods totalling more than $20 goods totalling more than $00 have discount card No discount Actions 5% discount 0% discount [5] UCLES /42/M/J/5

64 7 64 (c) The simplified table produced in part (b) is used as a design for program code. The following identifier table shows the parameters to be passed to the function Discount. This function returns the discount amount as an integer. Identifier GoodsTotal HasDiscountCard Data type INTEGER BOOLEAN Write program code for this function. Programming language [6] UCLES /42/M/J/5 [Turn over

65 A payroll program is to be written using an object-oriented programming language. An Employee class is designed. Two subclasses have been identified: HourlyPaidEmployee who is paid a monthly wage calculated from their hourly rate of pay and the number of hours worked during the month SalariedEmployee who is paid a monthly wage which is one 2th of their annual salary (a) Draw an inheritance diagram for these classes. (b) The design for the Employee class consists of: properties EmployeeName EmployeeID AmountPaidThisMonth methods SetEmployeeName SetEmployeeID CalculatePay Write program code for the class definition of the superclass Employee. Programming language [5] [3] UCLES /42/M/J/5

66 9 66 (c) (i) State the properties and/or methods required for the subclass HourlyPaidEmployee.... [4] (ii) State the properties and/or methods required for the subclass SalariedEmployee.... [2] (d) Name the feature of object-oriented program design that allows the method CalculatePay to be declared in the superclass Employee [] UCLES /42/M/J/5 [Turn over

67 Data is stored in the array NameList[:0]. This data is to be sorted. (a) (i) Complete the pseudocode algorithm for an insertion sort. FOR ThisPointer 2 TO... // use a temporary variable to store item which is to // be inserted into its correct location Temp NameList[ThisPointer] Pointer ThisPointer WHILE (NameList[Pointer] > Temp) AND... // move list item to next location NameList[...] NameList[...] Pointer... ENDWHILE // insert value of Temp in correct location NameList[...]... ENDFOR [7] (ii) A special case is when NameList is already in order. The algorithm in part (a)(i) is applied to this special case. Explain how many iterations are carried out for each of the loops.... [3] UCLES /42/M/J/5