Cambridge A Level Computer Science 9608 — 2016 May/June Paper 2 · Variant 3

This document consists of 16 printed pages. DC (LK/SG) 106693/4 © UCLES 2016 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level * 7 9 1 1 8 0 0 7 3 8 * COMPUTER SCIENCE 9608/23 Paper 2 Fundamental Problem-solving and Programming Skills May/June 2016 2 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.

2 9608/23/M/J/16 © UCLES 2016 There is an Appendix on the last page. Some questions will refer you to this information. 1 The items in the table below are statements from a program in a generic programming language. For the built-in functions list, refer to the Appendix on the last page. (a) (i) Show what type of programming construct each statement represents. Complete the table by putting a tick (✓) in the appropriate column for each item. Item Statement Selection Iteration Assignment 1 WHILE DegF > 37.5 2 MyName = "Gordon" 3 DegF = INT(DegF) 4 ENDIF 5 CASE OF MyFavourite 6 UNTIL x = 5 [6]

3 9608/23/M/J/16 © UCLES 2016 [Turn over (ii) State the purpose of each statement in the table in part (a)(i). Do not use mathematical symbols in your descriptions. Item Purpose of statement 1 … … 2 … … 3 … … 4 … … 5 … … 6 … … [6] (iii) Evaluate the following expressions when MyString has the value "Corrective Maintenance": Expression Evaluates to 'P' & MID(MyString, 13, 4) RIGHT(MID(MyString, 6, 10) ,4) [2]

4 9608/23/M/J/16 © UCLES 2016 2 The engine management system of a car includes an energy-saving facility. When certain conditions are met, this facility will automatically stop the engine. The system is to be software-based. It will include a subroutine, EnergySaver, which repeatedly takes data from sensors in the car. The subroutine decides whether or not to set the EngineStop value. The table of identifiers used by this subroutine is shown below. (a) Complete the identifier table below by stating the data types. Identifier Data type Description Accelerator … Accelerator pedal position Values: 0 to 100 in steps of 1 Meaning: 0: none (not pressed) 100: maximum (fully pressed) EngineTemp … Engine temperature in °C (-50 to +150 stored to 1 decimal place) NormalTemp … Normal engine temperature in °C Whole number; typical value 90 Speed … Road speed of car (in km/hr) Values: 0 to 200 in steps of 1 EngineStop … Value used to signal engine must be stopped Possible values: TRUE: stop engine FALSE: run engine [5] The condition for stopping the engine is that all three of the following are true: • Accelerator is not pressed • Engine temperature is normal or above • Car speed is zero

5 9608/23/M/J/16 © UCLES 2016 [Turn over The initial design stage will produce a prototype of EnergySaver, with a user interface. The structured English for this is: 1. INPUT value for accelerator pedal position 2. INPUT value for engine temperature 3. INPUT value for normal engine temperature 4. INPUT value for car speed 5. EVALUATE engine stopping condition 6. IF stopping condition satisfied SET engine stop value to TRUE 7. IF stopping condition not satisfied SET engine stop value to FALSE 8. OUTPUT message indicating engine stop value (b) Write the pseudocode equivalent of the structured English. Use the identifiers from the table in part (a). For the built-in functions list, refer to the Appendix on the last page. … … … … … … … … … … … … … … …[6]

6 9608/23/M/J/16 © UCLES 2016 3 String encryption was implemented using a simple character-substitution method. A function, Decrypt, is needed to reverse the encryption process and return the original character. The encryption uses the 7-bit ASCII value for each character. This value is used as an index for a 1D array, Lookup, which contains the substitute characters. Lookup contains an entry for each of the ASCII characters. This function, Decrypt, will accept two parameters, a single character, CipherChar, and the 1D array, Lookup. The steps involved in Decrypt are follows: • Search for the character in the array • Note the index value where the character is found (the index value is the ASCII value of the original character) • Use the index value to obtain the original character (a) The first attempt at writing the pseudocode for this function is shown below. Complete the pseudocode. For the built-in functions list, refer to the Appendix on the last page. FUNCTION Decrypt(… , …) RETURNS CHAR DECLARE Found : … DECLARE … : INTEGER DECLARE OriginalChar : CHAR Index 1 // … Found FALSE //search for CipherChar in Lookup: WHILE … //compare CipherChar with this array element: IF … THEN …//Set the flag ELSE Index …//Move to next array element ENDIF ENDWHILE //dropped out of loop so must have found CipherChar: …//convert Index to original character RETURN … ENDFUNCTION [11]

7 9608/23/M/J/16 © UCLES 2016 [Turn over Question 3 continues on page 8.

8 9608/23/M/J/16 © UCLES 2016 (b) A program is to be written to output part of the Lookup array. The design of the algorithm is shown below. It may be assumed that the characters output from Lookup are all printable. START Input StartIndex and NumberToOutput Produce OriginalChar from Index (using built-in function) Assign current array element to CipherChar Increment Index Output message line (see examples on the next page) End of loop? STOP YES NO Index StartIndex Loop

9 9608/23/M/J/16 © UCLES 2016 [Turn over For example, for the input of 65 and 3, the output will be: Index 65: Character A has substitute character Y Index 66: Character B has substitute character Q Index 67: Character C has substitute character F Write program code to implement the flowchart design. In addition to the Lookup array, assume that the following variables have been declared: StartIndex, NumberToOutput, Index Programming language … … … … … … … … … … … … … … … [6]

10 9608/23/M/J/16 © UCLES 2016 4 (a) Name two features of your chosen high-level programming language that support the implementation of a modular design. 1 … 2 … [2] (b) (i) The structure chart shows part of the design of a program for an online shopping system. The user has already added a number of products to their virtual basket. Draw on the chart, the symbol to show that the process of modifying the basket contents may be iterated (repeated). Modify Basket Contents Input product data Change product quantity Remove product F D E C A B [1] (ii) Each arrow in the structure chart above represents a parameter. The table below shows the three data items that the six parameters pass between modules. Tick (✓) to match each parameter to the correct data item. Data item Parameter A B C D E F Product ID Quantity Flag Value – indicating operation success or fail [4]

11 9608/23/M/J/16 © UCLES 2016 [Turn over 5 Claudia stores her large collection of music CDs in different places. Claudia wants to record where she stores each CD. She decides to write a program to do this. Data items for a typical CD are: Title: Kind of Green Artist: Miles Coltrane Location: Rack3-23 The data is to be stored in a text file, MyMusic. Each line of the text file will be a string, formed by concatenating the three data items. Before concatenation, the title and artist will each be made into a fixed-length string of 40 characters. Space characters may need to be added to each data item. The location is always 8 characters long. (a) (i) Explain the benefit of making the stored data into fixed-length strings. … … … … State a drawback of this file design. … … [3]

12 9608/23/M/J/16 © UCLES 2016 (ii) When Claudia buys a new CD, the CD data must be added to the existing file, MyMusic. She has written a procedure in pseudocode. This has the following file-handling statements: OPENFILE "MyMusic" FOR WRITE WRITEFILE "MyMusic", OutputString CLOSEFILE "MyMusic" There is a problem with the logic of this pseudocode. State the problem. … … Identify the effect it will have if the final code is implemented in this way. … … Give a possible solution. … … [3] (b) Claudia needs to output a list of all the CDs in a particular location. She designs a procedure, OutputLocationList, to do this. She also chooses the following identifiers: Identifier Data type CDTitle STRING CDArtist STRING CDLocation STRING The procedure will: • prompt for the name of the location • input the location (such as “Rack3-23”) • search the file for all CDs at this location • output the title and artist of each CD found • output the total number of CDs found at that location (such as “17 CDs found”)

13 9608/23/M/J/16 © UCLES 2016 [Turn over Write program code for the procedure OutputLocationList. Visual Basic and Pascal: You should include the declaration statements for variables. Python: You should show a comment statement for each variable used with its data type. Programming language … … … … … … … … … … … … … … … … … … … … … [10]

14 9608/23/M/J/16 © UCLES 2016 6 A string-handling function has been developed. For the built-in functions list, refer to the Appendix on the last page. The pseudocode for this function is shown below. FUNCTION SF(ThisString : STRING) RETURNS STRING DECLARE x : CHAR DECLARE NewString : STRING DECLARE Flag : BOOLEAN DECLARE m, n : INTEGER Flag TRUE NewString "" m LENGTH(ThisString) FOR n 1 TO m IF Flag = TRUE THEN x UCASE(MID(ThisString, n, 1)) Flag FALSE ELSE x LCASE(MID(ThisString, n, 1)) ENDIF NewString NewString & x IF x = " " THEN Flag TRUE ENDIF ENDFOR RETURN NewString ENDFUNCTION (a) (i) Complete the trace table below by performing a dry run of the function when it is called as follows: SF("big BEN") n x Flag m NewString [4]

15 9608/23/M/J/16 © UCLES 2016 [Turn over (ii) Describe the purpose of function SF. … … … …[2] (b) Test data must be designed for the function SF. (i) State what happens when the function is called with an empty string. … …[1] (ii) The function should be thoroughly tested. Give three examples of non-empty strings that may be used. In each case explain why the test string has been chosen. String … Explanation … … String … Explanation … … String … Explanation … … [3]

16 9608/23/M/J/16 © UCLES 2016 Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. 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 www.cie.org.uk after the live examination series. Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge. Appendix Built-in functions (Pseudocode) In each function below, if the function call is not properly formed, the function returns an error. MID(ThisString : STRING, x : INTEGER, y : INTEGER) RETURNS STRING returns the string of length y starting at position x from ThisString Example: MID("ABCDEFGH", 2, 3) will return string "BCD" LEFT(ThisString : STRING, x : INTEGER) RETURNS STRING returns the leftmost x characters from ThisString Example: LEFT("ABCDEFGH", 3) will return string "ABC" RIGHT(ThisString: STRING, x : INTEGER) RETURNS STRING returns the rightmost x characters from ThisString Example: RIGHT("ABCDEFGH", 3) will return string "FGH" CHR(x : INTEGER) RETURNS CHAR returns the character whose ASCII value is x Example: CHR(87) will return 'W' ASC(x : CHAR) RETURNS INTEGER returns the ASCII value of character x Example: ASC('W') will return 87 LCASE(x : CHAR) RETURNS CHAR returns the lower case equivalent character of x Example: LCASE('W') will return 'w' UCASE(x : CHAR) RETURNS CHAR returns the upper case equivalent character of x Example: UCASE('h') will return 'H' INT(x : REAL) RETURNS INTEGER returns the integer part of x Example: INT(27.5415) will return 27

® IGCSE is the registered trademark of Cambridge International Examinations. This document consists of 12 printed pages. © UCLES 2016 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level COMPUTER SCIENCE 9608/23 Paper 2 Written Paper May/June 2016 MARK SCHEME Maximum Mark: 75 Published 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 2016 series for most Cambridge IGCSE®, Cambridge International A and AS Level components and some Cambridge O Level components.

Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2016 9608 23 © Cambridge International Examinations 2016 1 (a) (i) [6] Item Statement Selection Iteration Assignment 1 WHILE DegF > 37.5
2 MyName = "Gordon"
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4 ENDIF
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One mark per row Additional ticks in any row cancels that row (ii) [6] Item Purpose of statement 1 (Start of) loop – repeat while DegF greater than 37.5 2 Assign (string) "Gordon" to MyName 3 Assign integer value / whole number part of DegF to DegF 4 End of an IF statement / selection statement 5 Head of CASE / selection statement based on variable MyFavourite 6 End of REPEAT / post-condition loop: repeated until x equals 5 Exact wording not important Explanation must refer to variables or values used in code (except for row 4) (iii) [2] Expression Result 'P' & MID(MyString, 13, 4) "Paint" RIGHT(MID(MyString, 6, 10), 4) "Main" Must have correct case Quotation marks optional

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2016 9608 23 © Cambridge International Examinations 2016 2 (a) [5] Identifier Data Type Description Accelerator INTEGER Accelerator position Values: 0 to 100 in steps of 1 Meaning: 0 : none (not pressed) 100: maximum (fully pressed) EngineTemp REAL / FLOAT / SINGLE / DOUBLE Engine temperature in °C (–50 to +150 correct to 1 decimal place) NormalTemp INTEGER Normal engine temperature in °C Whole number; typical value 90 Speed INTEGER Road speed of car (in km/hr) Values: 0 to 200 in steps of 1 EngineStop BOOLEAN Value used to signal engine must be stopped Possible values: TRUE: stop engine FALSE: run engine One mark per row Data types as shown

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Page 7 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2016 9608 23 © Cambridge International Examinations 2016 5 (a) (i) Explanation: [Max 3] • Easier to separate the two strings // to retrieve / search for / edit (text relating to a CD) • Obvious where CDTitle ends and CDArtist begins Drawback: • Takes up more / unnecessary space in the file • If the string is bigger than 40 characters then data will be lost // string length is limited • The additional spaces will need to be removed before strings can be used One mark per bullet (ii) Problem: File mode = WRITE / file is opened for writing // by explanation [3] Effect: All existing file lines / contents / data will be overwritten / deleted / lost Solution: WRITE should be changed to APPEND (allow meaningful example) Allow first two mark points to be interchanged – read as one paragraph.

Page 8 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2016 9608 23 © Cambridge International Examinations 2016 (b) 'Pseudocode' solution included here for development and clarification of mark scheme. Programming language example solutions appear in the Appendix. [Max 10] PROCEDURE OutputLocationList() DECLARE CDTitle : STRING DECLARE CDArtist : STRING DECLARE CDSearch : STRING DECLARE FileData : STRING DECLARE Total : INTEGER DECLARE FileData : STRING Total ← 0 OPENFILE "MyMusic" FOR READ OUTPUT "Input Location" INPUT CDSearch WHILE NOT EOF("MyMusic") READFILE ("MyMusic", FileData IF RIGHT(FileData, 8) = CDSearch THEN CDTitle ← LEFT(FileData, 40) CDArtist ← MID(FileData(41, 40) OUPUT (CDTitle & " – " & CDArtist) Total ← Total + 1 ENDIF ENDWHILE OUTPUT (Total & " CDs found" CLOSEFILE("MyMusic") ENDPROCEDURE One mark for each of the following: • Procedure heading and ending • Declaration AND initialisation of variable used as counter (Total above) • Prompt and input of location to search for CDSearch (or other name) • Open file for reading (Allow MyMusic or MyMusic.txt) • Working conditional loop structure including test for EOF The following points must be present inside a loop • Read a line from the file (or read complete file in one e.g. as list) • Isolate 8 chars representing location and compare with CDLocation • Extract strings representing CDTitle and CDArtist • Output CDTitle and CDArtist (separator optional) if correct location found • Increment Total if correct location found The following points must be present after a loop • Output message including number of CDs found at location (Total) • Close file

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Page 10 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2016 9608 23 © Cambridge International Examinations 2016 Appendix – Program Code Example Solutions Q3 (b): VB.NET Console.WriteLine("Enter start position") StartIndex = Console.ReadLine() Console.WriteLine("Enter how many") NumberToOutput = Console.ReadLine() For Index = StartIndex To StartIndex + NumberToOutput - 1 OriginalChar = Chr(Index) CipherChar = Lookup(Index) Console.WriteLine("Index " & Index & ": Character " & OriginalChar & " has substitute character " & CipherChar) Next Index Q3 (b): Pascal Writeln('Enter start position'); Readln(StartIndex); Writeln('Enter how many'); Readln(NumberToOutput); For index := StartIndex To StartIndex + NumberToOutput – 1 Do Begin OriginalChar := chr(index); CipherChar := Lookup[index]; writeln("Index " + index + ": Character " + OriginalChar + " has substitute character " & CipherChar); end; Q3 (b): Python startIndex = int(input("enter start position")) numberToOutput = int(input("enter how many")) for index in range(startIndex, (startIndex + numberToOutput)) : OriginalChar = chr(index) CipherChar = Lookup[index] print("Index " + (index) + ": Character " + OriginalChar + " has subst char " + CipherChar)

Page 11 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2016 9608 23 © Cambridge International Examinations 2016 Q5 (b): VB.NET A StreamReader() solution: Sub OutPutLocationList() Dim Total As Integer Dim FileData As String Dim ObjReader As IO.StreamReader ObjReader = New IO.StreamReader("C:\MyMusic.txt") Dim CDLocation As String Dim CDTitle As String Dim CDArtist As String Total = 0 Console.WriteLine("Input location to search ") CDSearch = Console.ReadLine Do While ObjReader.Peek <> -1 FileData = ObjReader.ReadLine() If Right(FileData, 8) = CDLocation Then CDTitle = Left(FileData, 40) CDArtist = Mid(FileData, 41, 40) Console.WriteLine(CDTitle & " " & CDArtist) Total = Total + 1 End If Loop Console.WriteLine(Total & " CDs were found") ObjReader.Close() End Sub A legacy FileOpen() solution: Sub OutPutLocationList() Dim Total As Integer Dim FileData As String FileOpen (1, "C:\MyMusic.txt", OpenMode.Input) Dim CDLocation As String Dim CDTitle As String Dim CDArtist As String Total = 0 Console.WriteLine("Input location to search ") CDSearch = Console.ReadLine Do While NOT EOF(1) Input(1, FileData) If Right(FileData, 8) = CDSearch Then CDTitle = Left(FileData, 40) CDArtist = Mid(FileData, 41, 40) Console.WriteLine(CDTitle & " " & CDArtist) Total = Total + 1 End If Loop Console.WriteLine(Total & " CDs were found") FileClose(1) End Sub

Page 12 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2016 9608 23 © Cambridge International Examinations 2016 Q5 (b): Pascal procedure OutputLocationList; var FileData, CDLocation, CDTitle, CDArtist : String; CDFile : Textfile; Total : Integer; Begin Total := 0; Writeln('Input location to search '); Readln(CDSearch); AssignFile(CDFIle, 'MyMusic.txt'); Reset(CDFile); While not eof(CDFile) Do Begin readln(CDFile, FileData); If copy(FileData, 80, 8) = CDSearch Then Begin CDTitle := copy(FileData, 1, 40); CDArtist := copy(FileData, 41, 40); Writeln(CDTitle + ‘ : ‘ + CDArtist); Total := Total + 1; End; End; Writeln(Total + ‘ CDs were found’) CloseFile(CDFile); End Q5 (b): Python #total : Integer #CDSearch, LineOfText, LineString : String Def OutPutLocationList(): FileHandle = open("MyMusicPy.TXT", "r") total = 0 CDSearch = input("Enter location to search") LineOfText = FileHandle.readline() while len(LineOfText) > 0: LineString = LineOfText[80:87] #extact last 8 characters (location) if LineString == CDSearch: total = total+1 CDTitle = LineOfText[0:39] #extract CD title CDArtist = LineOfText[40:79] #extract CD artist print(CDTitle + ": " + CDArtist) LineOfText = FileHandle.readline() #read next line print("There are " + str(total) + " in that location") FileHandle.close()