9618 Computer Science June 2024 Question paper 21

1 An algorithm is developed in pseudocode before being coded in a programming language.

(a) The following table shows four valid pseudocode assignment statements.

Complete the table by giving an appropriate data type to declare each of the variables A, B, C and D. Assignment statement Data type A LEFT(MyName, 1) B Total * 2 C INT(ItemCost) / 3 D "Odd OR Even"

[4]

(b) Other variables in the program have example values as shown: Variable Value Sorted False Tries 9 ID "ZGAC001"

Complete the table by evaluating each expression, using the example values. Expression Evaluates to Tries < 10 AND NOT Sorted Tries MOD 4 TO_LOWER(MID(ID, 3, 1)) LENGTH(ID & "xx") >= Tries

[4]

(c) The variable names A, B, C and D in part (a) are not good programming practice.

(i) State why these variable names are not suitable [1]

(ii) Identify one problem that these variable names might cause [1]

(iii) The choice of suitable variable names is one example of good programming practice.

Give one other example [1]

4 A global 1D array Data contains 100 elements of type integer.

A function Check() will: • total the element values in odd index locations (1, 3, 5 ... 97, 99) • total the element values in even index locations (2, 4, 6 ... 98, 100) • return one of three strings ‘Odd’, ‘Even’ or ‘Same’ to indicate which total is the greater, or whether the totals are the same.

Write pseudocode for the function Check() [6]

2 An algorithm has three steps. It will:

repeatedly input a pair of numeric values A and B

count the number of pairs that are input until A has been greater than B 10 times

output the number of pairs that were input.

(a) Complete the program flowchart.

START END INPUT A, B Yes No [5]

(b) Step 1 of the algorithm is changed.

A variable ThisSequence is used to enter a sequence of 10 pairs of numeric values, using a single input statement.

Following the input of ThisSequence the revised algorithm will extract the pairs of numbers.

Describe the variable ThisSequence and how the numbers are extracted [2]

3 The diagram shows an Abstract Data Type (ADT) representation of a linked list after data items have been added. • PS is the start pointer. • PF is the free list pointer. • Labels Df, Dc, Db and Dy represent the data items of nodes in the list. • Labels Fg, Fh, Fm and Fw represent the data items of nodes in the free list. • The symbol Ø represents a null pointer.

Df PS Dc Db Dy Ø Fg PF Fh Fm Fw Ø

(a) Describe the linked list immediately after initialisation, before any data items are added [3]

(b) A program will be written to include a linked list to store alphanumeric user IDs.

The design uses two variables and two 1D arrays to implement the linked list.

Each array element contains data of a single data type and not a record.

The statements below describe the design.

Complete the statements. The two variables will be of type The two variables will be used as to the arrays. The values stored in the two variables will indicate The first 1D array will be of type The first 1D array will be used to The second 1D array will be of type The second 1D array will be used to [5]

5 A global 1D array of strings contains three elements which are assigned values as shown:

Data[1] "aaaaaa"

Data[2] "bbbbbb"

Data[3] "cccccc"

Procedure Process() manipulates the values in the array.

The procedure is written in pseudocode as follows:

PROCEDURE Process(Format : STRING)

DECLARE Count, Index, L : INTEGER

DECLARE Result : STRING

DECLARE C : CHAR

Result "****"

FOR Count 1 TO LENGTH(Format) STEP 2

C

MID(Format, Count, 1)

L

STR_TO_NUM(MID(Format, Count + 1, 1))

Index

(Count + 1) DIV 2

CASE OF C

  'X' : Result

TO_UPPER(Data[Index])

  'Y' : Result

TO_LOWER(Data[Index])

  'Z' : Result

"**" & Data[Index]

ENDCASE

Data[Index]

LEFT(Result, L)

NEXT Count

ENDPROCEDURE

(a) Complete the trace table by dry running the procedure when it is called as follows:

CALL Process("X3Y2W4") Count C L Index Result Data[1] Data[2] Data[3]

[6]

(b) The procedure is to be modified. If variable C is assigned a value other than 'X', 'Y' or 'Z', then procedure Error() is called and passed the value of variable C as a parameter.

This modification can be implemented by adding a single line of pseudocode.

(i) Write the single line of pseudocode [1]

(ii) State where this new line should be placed [1]

6 Three points on a grid form a triangle with sides of length A, B and C as shown in the example:

10 y x 9 8 7 6 5 4 1 0 2 3 4 5 6 7 8 9 10 A C B 3 2 1

A triangle is said to be right-angled if the following test is true (where A is the length of the longest side):

A2 = B2 + C2

A2 means A multiplied by A, for example 32 means 3 × 3 which evaluates to 9

You can calculate A2, B2 and C2 by using the coordinates of the endpoints of each line.

For example, B2 is calculated as follows:

10 y x 9 8 7 6 5 4 1 0 2 3 4 5 6 7 8 9 10 B P2 P2 P1 P1 3 2 1 (x1, y1) (x1, y1) (x2, y2) (x2, y2)

The endpoints, P1 and P2, have the coordinates (3, 2) and (6, 6).

The value B2 is given by the formula:

B2 = (x1 − x2)2 + (y1 − y2)2

In this example:

B2 = (3 − 6)2 + (2 − 6)2

B2 = (–3)2 + (–4)2

B2 = 9 + 16

B2 = 25

(a) A function IsRA() will: • take three sets of integers as parameters representing the coordinates of the three endpoints that form a triangle • return TRUE if the endpoints form a right-angled triangle, otherwise return FALSE.

In pseudocode, the operator ‘^’ represents an exponent, which is the number of times a value is multiplied by itself. For example, the expression Value2 may be written in pseudocode as Value ^ 2

Complete the pseudocode for the function IsRA().

FUNCTION IsRA(x1, y1, x2, y2, x3, y3 : INTEGER) RETURNS BOOLEAN ENDFUNCTION

[6]

(b) The test used to check if a triangle is right-angled can be written in two ways:

A2 = B2 + C2

or

A = √(B2 + C2)

The symbol √ represents the square root operation. For example, √81 = 9

A new function SQRT() is written to perform the square root operation. The function takes an integer number as a parameter and returns a positive real value representing the square root of the number.

During testing it is found that the SQRT() function returns a value that is only accurate to 4 decimal places.

For example, SQRT(25) returns 5.0000125 rather than the correct value of 5.0

The function IsRA() from part (a) is modified to use the new SQRT() function to test if a triangle is right-angled.

Describe a problem that might occur when using the modified IsRA() function and suggest a solution that still allows the SQRT() function to be used. Problem Solution [2]

7 A fitness club has a computerised membership system. The fitness club offers a number of different exercise classes.

The following information is stored for each club member: name, home address, email address, mobile phone number, date of birth and the exercise(s) they are interested in.

(a) When an exercise class is planned, a new module will send personalised text messages to each member who has expressed an interest in that exercise. Members wishing to join the class send a text message back. Members may decide not to receive future text messages by replying with the message ‘STOP’.

The process of abstraction is used to filter out unnecessary information.

(i) State one advantage of applying abstraction to this problem [1]

(ii) Identify three items of information that will be required by the new module.

Justify your choices with reference to the given scenario. Item 1 required Justification Item 2 required Justification Item 3 required Justification [3]

(iii) Identify two operations that would be required to process data when the new module receives a text message back from a member. Operation 1 Operation 2 [2]

(b) The structure chart illustrates part of the membership program: Sub-A Sub-B P1 T1 P2 Name Update Sub-C A

Data item notes: • Name contains the name of a club member • P1 and T1 are of type real.

(i) Explain the meaning of the diamond symbol (labelled with the letter A) in the chart [2]

(ii) Write the pseudocode module headers for Sub-A and Sub-B.

Sub-A Sub-B [4]

8 A teacher is designing a program to process pseudocode projects written by her students.

Each student project is stored in a text file.

The process is split into a number of stages. Each stage performs a different task and creates a new file named as shown: File name Comment MichaelAday_src.txt student project file produced by student Michael Aday MichaelAday_S1.txt file produced by stage 1 MichaelAday_S2.txt file produced by stage 2

The teacher has defined the first program module as follows: Module Description DeleteComment() • called with a parameter of type string representing a line of pseudocode from a student’s project file • returns the line after removing any comments Note on comments: A comment starts with two forward slash characters and includes all the remaining characters on the line. The following example shows a string before and after the comment has been removed: Before: IF X2 > 13 THEN //check if limit exceeded After: IF X2 > 13 THEN

(a) Complete the pseudocode for module DeleteComment().

FUNCTION DeleteComment(Line : STRING) RETURNS STRING ENDFUNCTION

[8]

(b) A second module is defined: Module Description Stage_1() • called with a parameter of type string representing a student name • creates a new stage 1 file • copies each line from the student’s project file to the stage 1 file after removing any comment from each line • does not write blank lines to the stage 1 file • returns the number of lines written to the stage 1 file

Write pseudocode for module Stage_1().

Module DeleteComment() must be used in your solution [7]