9608_w21_qp_31
A paper of Computer Science, 9608
Questions:
7
Year:
2021
Paper:
3
Variant:
1
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1
Data types can be defined using pseudocode. The data type, ComputerRecord, is defined by the following pseudocode: TYPE ComputerRecord DECLARE ComputerID : INTEGER DECLARE ComputerType : (Laptop, Desktop, Tablet) DECLARE ComputerLocation : (Lab1, Lab2, Lab3, Mobile) DECLARE DateTested : DATE ENDTYPE A variable, SchoolComputer, is declared in pseudocode as: DECLARE SchoolComputer : ComputerRecord Write pseudocode statements to assign 1234 to the ComputerID of SchoolComputer and Lab2 to the ComputerLocation of SchoolComputer. The type definition for ComputerRecord is changed. The definition has been extended to include the student identification numbers, StudentID, for up to 20 students who can use that computer. Each student identification number is an integer. Write the extra line of pseudocode needed in the type definition for ComputerRecord. The values for the field ComputerID must be between 1000 and 1999 inclusive. Rewrite one pseudocode line from the type definition of ComputerRecord to implement the change. Data about all the computers are stored in a file that uses random file organisation. ComputerID is used as the key field. Explain how a program could search for a record stored in this file.
3. Advanced Theory  →  3.1. Data representation
2. Fundamental Problem-solving and Programming Skills  →  2.1. Algorithm design and problem-solving
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4
The truth table for a logic circuit with four inputs is shown. INPUT OUTPUT P Q R S X Write the Boolean algebraic expression for the truth table as a sum-of-products. X = Complete the following Karnaugh Map (K-map) for the truth table. PQ RS The K-map can be used to simplify the expression in part . Draw looparound appropriate groups in the K-map to produce an optimal sum-of-products. Write the simplified sum-of-products from the K-map. X = Simplify the expression for X, as represented by the truth table in part , using Boolean Algebra.
3. Advanced Theory  →  3.3. Hardware
1. Theory Fundamentals  →  1.3. Hardware
Open
5
Flora has written a program that uses the variables a, b, c and d. Part of the program contains the following calculations: a = 2 b = 5 c = 7 d = a * b – (a + b + c) Write the Reverse Polish Notation (RPN) for the expression: a * b – (a + b + c) Show the changing contents of the stack as the value for variable d is calculated from the RPN expression. Convert the following RPN expression back to its original infix form. d b * b c d + - + a / Explain why expressions are evaluated using RPN.
3. Advanced Theory  →  3.4. System software
2. Fundamental Problem-solving and Programming Skills  →  2.3. Programming
4. Further Problem-solving and Programming Skills  →  4.1. Computational thinking and problem-solving
Open
6
Mohammad is working away from his company’s head office. He wants to send a secure message over a computer network to the head office. Explain the way in which a digital signature for the message would be produced. State two reasons why a digital signature for the message is required. The message is encrypted using asymmetric key cryptography before it is sent and decrypted when it arrives at the head office. Describe this process of encrypting and decrypting the message. State one reason for using asymmetric key cryptography.
3. Advanced Theory  →  3.5. Security
Open
7
A large apartment block has 20 floors. On each floor there is one security camera and four sensors. The image from each security camera is output to a display screen for that floor. • There are 20 display screens in the reception area on the lowest floor. • The data from the sensors are read and processed by a computer system. • Warning messages can also be displayed on each display screen. Identify the type of system described. Justify your answer to part . Identify two types of sensor that could be used by this system. State a reason for the use of each sensor. Sensor 1 Reason Sensor 2 Reason A program regularly checks each sensor’s readings. If the value of the reading is out of range, a warning message is displayed on the screen for that floor. A pseudocode algorithm to output the warnings has been written using these identifiers. Identifier Data type Description FloorNumber INTEGER Floor number SensorNumber INTEGER Sensor number Always BOOLEAN Value to ensure continuous loop The pseudocode algorithm uses: • the function CheckSensor(Floor, Sensor) that returns TRUE if the sensor reading is out of range and FALSE otherwise • the procedure ScreenOut(Floor, Sensor) that outputs the warning message "Problem on Floor" to the appropriate screen. Complete the pseudocode algorithm. 01 Always ………………………………………………………………………… 02 REPEAT 03 FOR FloorNumber 1 TO ………………………………………………………………………… 04 FOR SensorNumber 1 TO ………………………………………………………………………… 05 IF CheckSensor(FloorNumber, SensorNumber) 06 THEN 07 ScreenOut(FloorNumber, SensorNumber) 08 ENDIF 09 ENDFOR 10 ENDFOR 12 // delay loop 13 // delay loop 14 UNTIL ………………………………………………………………………… Write a delay loop in pseudocode for lines 12 and 13 of the pseudocode algorithm. If a sensor reading is out of range, a bit is set in a memory location allocated to that floor. The addresses for the memory locations are 401 to 420. For example, memory location 401 is used to store the status of the sensors 1 to 4 on floor 1, memory location 402 is used to store the status of the sensors 1 to 4 on floor 2. The table shows data for some of the floors, with sensor 1 on floor 1 set, sensor 2 on floor 2 set and sensors 3 and 4 on floor 20 set. Bits Memory location Sensor number Floor … … … … … … … … … … The data in memory location 410 is shown. State what this data represents. Explain the way in which the data from sensor 3 on floor 7 can be checked. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cambridgeinternational.org after the live examination series.
2. Fundamental Problem-solving and Programming Skills  →  2.1. Algorithm design and problem-solving
Open