MSHS 2018 P1 solution

Class Index Number Name MARIS STELLA HIGH SCHOOL PRELIMINARY EXAMINATIONS SECONDARY FOUR COMPUTING 7155/01 Paper 1 Written 24 Aug 2018 2 hours Candidates answer on the Question Paper No Additional Materials are required. Mark Scheme For Examiner’s Use This document consists of 10 printed pages. 80

2 1 (a) Convert the denary number 4351 into a hexadecimal number. Show your working. Denary Quotient Remainder 4351 271 15 271 16 15 16 1 0 1 0 1 The hexadecimal equivalent of 4351 is 10FF. [2] (b) Convert the binary number 11010101 into a denary number. Show your working. 128 64 32 16 8 4 2 1 27 26 25 24 23 22 21 20 1 1 0 1 0 1 0 1 128+64+16+4+1 = 213 The denary equivalent of 11010101 is 213. [2] (c) Describe two common uses of the hexadecimal number system. RGB colour codes – hexadecimal number is used to express the intensities of red, green and blue light in the form of #RRGGBB this allows HTML and CSS users to change site colours to required colours based on the number keyed in. Memory Dump – hexadecimal number system is deal for displaying every byte in memory used by the program in a compact manner. Allowing experience programmers to interpret and work out the cause of program failure. Network Addresses – hexadecimal numbers are used to express the unique internet protocol address in a more compact way. It is also used to express computer Media Access Control (MAC) address which identify each hardware device uniquely. ASCII and Unicode – Hexadecimal number is used to express different characters in languages other than English as a standard that can be used all over the world. URL Encoding – Hexadecimal number is used in Uniform Resource Locator (URL) to represent reserved characters that is part of a web address. [4]

3 2. Insert six of the following words about types of software licences in the correct places in the text below. Most commercial software are under legal protection and copyright, and they are also known as proprietary software. Unauthorised copying is illegal and majority of the source code is kept secret. Only after these legal protection have expired, been surrendered or are simply inapplicable would these programs become public domain software. A type of software known as freeware is similar to proprietary software except that it is available for use at no cost. It usually allows users to try a limited version of the software. While shareware is usually the demonstration software that is distributed for free for a specific evaluation period. [6] 3 Computer networks are common nowadays. Most homes are equipped with a simple modem and a router to link the mobile devices at home to the same network. Identify two other network devices. In each case, explain the function of the device. Network Interface Card (NIC) Provides the hardware interface to enable the transfer of data between a device and a network. Usually built-in in most devices, the NIC has a unique 48-bit MAC address that can be used to identify the computer or device its connected to. Network Hub Connects multiple devices to the same network. It transfers received packets to all devices connected to the hub, like a broadcast. However, it does not store any information about the connect devices. Network Bridge Connects two similar networks together to form a single network. Used to connect 2 LANs using the same protocol. The bridge uses MAC addresses to keep track of all devices connect to it and is able to decide if it requires to forward or drop packets when it receives data packets. [6]

4 4 Your Co-Curricular Activities (CCA) club wants to organise an enrichment activity for its members. Each student is given 3 enrichment activities to choose from. Your club wants to use a computer program to find out which students are interested in which enrichment activity and which is the most popular choice. There are 60 students in the club. State the inputs, the outputs and the processes required to find the most popular enrichment activity and the names of the students who chose that enrichment activity. Inputs - 60 students’ names - 60 students’ choices (1 of 3 possible enrichment programs) Output - Enrichment with most names - List of names who chose enrichment Process - Store names and choices into list - Split names into 3 different list based on name of enrichment - Count number of names in each list [6] 5 There are three main types of program errors that can occur in programming. (a) A student was asked to write a program that asks for integer and returns the value of that integer multiplied by 5. The program would be required to check that only numbers are accepted. The student wrote the following code. 1 2 3 4 5 number = input(“Please enter a number. “) while not number.isdigit: number = input(“Please enter numbers only. “) answer = number * 5 print(answer) The student made 2 mistakes in the programming code above. That caused his output to be undesirable. You are required to do the following: • locate which lines the errors are in • for each error, identify what type of error it is • explain why it is an error • what should be done to correct the error Line 2 Syntax Error The use of function isdigit, requires the “()” to be completed. The correction should be number.isdigit() Line 4 Logic Error Since the program is required to output the value of the input number multiply by 5, the answer = number * 5 requires “number” to be integer. However, at that step, number stores the value in a string. So, the output will be 5 of that number string together.

5 The correction should be answer = int(number)*5 (b) (i) State the third type of error that is not found in part (a). (ii) Describe with an example why such an error occurs and what will it cause. i) The last error is Run-time errors. ii) This error occurs by incorrect use of commands, input data that has not been properly validated or running out of memory. This will result in the program crashing or hanging. An example would be a program that is required to add 2 to the number that is input. num1 = 2 num2 = input(“Enter integer”) print (num1+num2) and the inputs given is seven. A run time error will occur here. [4] 6 Five statements about compilers and interpreters are shown. Tick (√) to show whether the statement refers to a compiler or to an interpreter. Statement Interpreter Compiler Takes one statement at a time and executes it √ Syntax errors are detected before the program runs √ Translates the whole program in one go √ Easier to debug √ Resulting program runs at a faster speed √ [5] 7 Pharming is a type of cyber-attack; describe two safety measures that businesses could use to prevent pharming. Two from: - Use regularly updated anti- virus program to protect against unauthorized alteration of the Host file. - Regularly patch your operating system and installed software. - Check the ‘HTTP’ address for ‘HTTPS’ which shows that the protocol used is secured - Check for the Padlock symbol that indicates a secure, encrypted connection. - Double check the spelling of the website. [2] [3]

6 8 Study the following flowchart of a program very carefully. (a) Complete the trace table for the following two sets of data: (i) a = 18, b = 34, c = 5, d = 55 (ii) a = 5, b = 9, c = 4, d = 1 START y = 1 y = a a = b INPUT a, b, c, d OUTPUT a, b, c, d END is a > b? b = y x = 1 x = 0 y = b b = c is b > c? c = y x = 1 y = c c = d is c > d? d = y x = 1 Yes No Yes No No Yes is x = 1? Yes No

7 a b c d x y OUTPUT