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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.

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" �

3 DegF = INT(DegF) �

4 ENDIF �

5 CASE OF MyFavourite �

6 UNTIL x = 5 �

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




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

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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.




(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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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)




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




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()

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