Computer Science 9618/23 October/November 2022: question paper and mark scheme

Question

A program is required for a shopping website. (a) Part of the program requires four variables. The following table describes the use of each variable. Complete the table by adding the most appropriate data type for each variable. Variable use Data type Store the number of days in the current month Store the first letter of the customer’s first name Store an indication of whether a year is a leap year Store the average amount spent per customer visit [4] (b) The designer considers the use of a development life cycle to split the development of the website into several stages. (i) State one benefit of a development life cycle when developing the website. …… [1] (ii) Analysis is one stage of a development life cycle. State one document that may be produced from the analysis stage of the website project. …… [1] (c) The program will be developed using the Rapid Application Development (RAD) life cycle. (i) State one principle of this life cycle. …… [1] (ii) Give two benefits and one drawback of its use compared to the waterfall life cycle. Benefit 1 …… Benefit 2 …… Drawback …… [3] (d) Adaptive maintenance needs to be carried out on the website program. Give two reasons why adaptive maintenance may be required. 1 …… 2 …… [2]

Question

A program is being designed for a smartphone to allow users to send money to the charity of their choice. Decomposition will be used to break the problem down into sub-problems. Identify three program modules that could be used in the design and describe their use. Module 1 …… Use …… Module 2 …… Use …… Module 3 …… Use …… [3]

Question

An algorithm is needed to process a sequence of numbers. Numbers may be positive or negative and may be integer or decimal. The algorithm will: • prompt and input one number at a time until the value zero is input • sum the negative numbers • sum the positive numbers • when zero is input, output the two sum values and then end. Describe the algorithm needed. Do not include pseudocode statements in your answer. …… [5]

Question

(a) A program contains a 1D array DataItem with 100 elements. State the one additional piece of information required before the array can be declared. …… [1] (b) A programmer decides to implement a queue Abstract Data Type (ADT) in order to store characters received from the keyboard. The queue will need to store at least 10 characters and will be implemented using an array. (i) Describe two operations that are typically required when implementing a queue. State the check that must be carried out before each operation can be completed. Operation 1 …… Check 1 …… Operation 2 …… Check 2 …… [4] (ii) Describe the declaration and initialisation of the variables and data structures used to implement the queue. …… [5]

Question

(a) A text string contains three data items concatenated as shown: <StockID><Description><Cost> Item lengths are: Item Length StockID 5 Description 32 Cost the remainder of the string A procedure Unpack() takes four parameters of type string. One parameter is the original text string. The other three parameters are used to represent the three data items shown in the table and are assigned values within the procedure. These values will be used by the calling program after the procedure ends. (i) Write pseudocode for the procedure Unpack(). …… [6] (ii) Explain the term procedure interface with reference to procedure Unpack(). …… [2] (b) The design changes and a record structure is defined to store the three data items. A user-defined data type StockItem is created as shown: TYPE StockItem DECLARE StockID : STRING DECLARE Description : STRING DECLARE Cost : REAL ENDTYPE (i) A variable LineData of type StockItem is declared. Write the pseudocode statement to assign the value 12.99 to the Cost field of LineData. …… [1] (ii) Procedure Unpack() is modified and converted to a function which takes the original text string as the only parameter. Explain the other changes that need to be made to convert the procedure into a function. …… [2] (c) Unpack() is part of a program made up of several modules. During the design stage, it is important to follow good programming practice. One example of good practice is the use of meaningful identifier names. Give the reason why this is good practice. Give two other examples of good practice. Reason …… Example 1 …… Example 2 …… [3] (d) The program that includes Unpack() is tested using the walkthrough method. Describe this method and explain how it can be used to identify an error. …… [3]

Question

Components are weighed during manufacture. Weights are measured to the nearest whole gram. Components that weigh at least 3 grams more than the maximum weight, or at least 3 grams less than the minimum weight, are rejected. A component is rechecked if it weighs within 2 grams of either the maximum or minimum weight. The final outcome of weighing each component is shown below: Outcome Weight Reject Max + 2 Recheck Max Maximum weight Max – 2 Accept Min + 2 Recheck Min Minimum weight Min – 2 Reject A function Status() will be called with three parameters. These are integers representing the weight of an individual component together with the minimum and maximum weights. The value returned from the function will be as follows: Outcome Return value Accept 'A' Reject 'R' Recheck 'C' (a) Complete the following test plan for five tests that could be performed on function Status(). The tests should address all possible outcomes. Test number Component weight Min Max Expected return value 1 'A' 2 3 4 5 [5] (b) Write pseudocode for Status(). …… [6]

Question

A teacher is designing a program to perform simple syntax checks on programs written by students. Two global 1D arrays are used to store the syntax error data. Both arrays contain 500 elements. • Array ErrCode contains integer values that represent an error number in the range 1 to 800. • Array ErrText contains string values that represent an error description. The following diagram shows an example of the arrays. Index ErrCode ErrText 1 10 "Invalid identifier name" 2 20 "Bracket mismatch" 3 50 "" 4 60 "Type mismatch in assignment" ... 500 999 <Undefined> Note: • There are less than 500 error codes so corresponding elements in both arrays may be unused. Unused elements in ErrCode have the value 999. These will occur at the end of the array. The value of unused elements in ErrText is undefined. • Values in the ErrCode array are stored in ascending order but not all values may be present. For example, there may be no error code 31. • Some error numbers are undefined. In these instances, the ErrCode array will contain a valid error number but the corresponding ErrText element will contain an empty string. The teacher has defined one program module as follows: Module Description • Prompts for input of two error numbers • Outputs a list of error numbers between the two numbers input (inclusive) together with the corresponding error description • Outputs a warning message when the error description is missing as for error number 50 in the example • Outputs a suitable header and a final count of error numbers found OutputRange() Output based on the example array data above: List of error numbers from 1 to 60 10 : Invalid identifier name 20 : Bracket mismatch 50 : Error Text Missing 60 : Type mismatch in assignment 4 error numbers output (a) Write pseudocode for module OutputRange(). Assume that the two numbers input represent a valid error number range. …… [8] Question 7 continues on the next page. (b) (i) Two additional modules are defined: Module Description SortArrays() • Sorts the arrays into ascending order of ErrCode • Takes two parameters: • an error number as an integer • an error description as a string • Writes the error number and error description to the first AddError() unused element of the two arrays. Ensures the ErrCode array is still in ascending order • Returns the number of unused elements after the new error number has been added • Returns −1 if the new error number could not be added Write pseudocode for the module AddError(). Assume that the error code is not already in the ErrCode array. …… [6] (ii) A new Module RemoveError() will remove a given error number from the array. Describe the algorithm that would be required. Do not include pseudocode statements in your answer. …… [3]