Structured Programming (Cambridge International A-Level Computer Science): Exam Questions

A program uses three global integer variables HH, MM and SS to represent the current time in hours, minutes and seconds using the 24-hour clock notation.

Midnight would be represented as 00:00:00 (HH:MM:SS). If the variables HH, MM and SS contained the values 16, 30 and 10 respectively, then the time would be 16:30:10 or just after 4.30 in the afternoon.

A procedure Tick() will be called every second. The procedure Tick() will:

• update the value in SS each time it is called
• update the values in HH and MM as appropriate
• call a procedure CheckAlarm() at the start of each minute
• call a procedure NewDay() whenever the time reaches midnight.

Complete the pseudocode for procedure Tick().

PROCEDURE Tick()

A program is being developed to process bank card information.

When a card number is displayed, all the characters except the last four are replaced with the asterisk character '*'.

Card numbers are stored as strings. The strings are between 10 and 20 characters in length.

The function Conceal() will take a string representing a card number and return a modified string.

Example strings:

The function Conceal() will:

• take a numeric string as a parameter representing the card number
• return a string in which the asterisk character replaces all except the last four characters of the card number parameter.

Write pseudocode for the function Conceal().

The requirements have been changed. Conceal() will now be written as a procedure which will process 100 card numbers each time it is called.

The card numbers will be stored in a 2D array CardNumber. The original string will be stored in column one and the modified string in column two.

The new procedure Conceal() will write the modified string to the corresponding element in column two.

The array CardNumber is passed as a parameter to the new procedure Conceal().

Identify how this parameter should be specified in the new procedure head

An alternative algorithm to determine if a paper needs to be checked uses a global 1D array Check, containing 76 elements of type BOOLEAN. The indices of the array are from 0 to 75 (inclusive), corresponding to the range of possible marks.

An element value in Check is TRUE if the index is within 2 marks of a grade boundary. For example, in the case where the C grade boundary is 43 the corresponding part of the Check array would be as follows:

A procedure GBInitialise() will initialise the Check array using values from the GB array.

Note it can be assumed that the maximum grade boundary value for A is 70 and the minimum value for E is 15.

Write pseudocode for the procedure.

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.

(ii) Identify one problem that these variable names might cause.

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

Give one other example.

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().

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

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:

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 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

The structure chart illustrates part of the membership program:

Data item notes:

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

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

Sub-A...........................................................................................

Sub-B...........................................................................................

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:

The teacher has defined the first program module as follows:

Complete the pseudocode for module DeleteComment().

FUNCTION DeleteComment(Line : STRING) RETURNS STRING

A triangle has sides of length A, B and C.

In this example, A is the length of the longest side.

This triangle is said to be right‑angled if the following equation is true:

A × A = (B × B) + (C × C)

A procedure will be written to check whether three lengths represent a right‑angled triangle. The lengths will be input in any sequence.

The procedure IsRA() will:

• prompt and input three integer values representing the three lengths
• test whether the three lengths correspond to the sides of a right‑angled triangle
• output a suitable message. The length of the longest side may not be the first value input.

The length of the longest side may not be the first value input.

Write pseudocode for the procedure IsRA().

A music player stores music in a digital form and has a display which shows the track being played.

Up to 16 characters can be displayed. Track titles longer than 16 characters will need to be trimmed as follows:

• Words must be removed from the end of the track title until the resulting title is less than 14 characters.
• When a word is removed, the space in front of that word is also removed.
• Three dots are added to the end of the last word displayed when one or more words have been removed.

The table below shows some examples:

A function Trim() will:

• take a string representing the original title
• return the string to be displayed.

Assume:

• Words in the original title are separated by a single space character.
• There are no spaces before the first word or after the last word of the original title.
• The first word of the original title is less than 14 characters.

Write pseudocode for the function Trim().

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.

For example:

The teacher has defined the first program module as follows:

Refer to the insert for the list of pseudocode functions and operators.

A program uses many complex algorithms.

One algorithm is repeated in several places. The code for the algorithm is the same wherever it is used, but the calculations within the algorithm may operate on different data.

The result of each calculation is used by the code that follows it.

It is decided to modify the program and implement the algorithm as a separate module.

(i) State two benefits of this modification to the existing program.

(ii) Describe how the modification would be implemented.

A procedure TwoParts() will input a sequence of real values, one at a time.

The procedure will:

• process the sequence in two parts
• form a first total by adding the values until the first zero
• form a second total by adding the values after the first zero until the second zero
• output the average of the two totals, together with a suitable message.

Values input in the first part are totalled using global variable TotalA and those input in the second part are totalled using global variable TotalB.

Write pseudocode for the procedure TwoParts().

A program displays a progress bar to inform the user of the progress of tasks that take a significant time to complete, such as those involving file transfer operations.

Task progress is divided into 11 steps. Each step represents the amount of progress as a percentage. An image is associated with each step and each image is stored in a different file.

Different progress bar images may be selected. For a given image, files all have the same filename root, with a different suffix.

The table illustrates the process for using the image with filename root BargraphA

A procedure Progress() will:

• be called with two parameters:

  • an integer representing the percentage progress (0 to 100 inclusive)
  • a string representing the image filename root

• generate the full image filename

• call a procedure Display() using the full image filename as the parameter.

Write pseudocode for procedure Progress().

The definition of procedure Progress() is provided here for reference

Progress() will be rewritten and a new module Progress2() produced with these requirements:

• an additional parameter of type integer will specify the total number of steps
• the image filename will be returned (procedure Display() will not be called from within Progress2()).

(i) Write pseudocode for the new module header.

(ii) State one benefit of increasing the number of steps.

Seven program modules form part of a program. A description of the relationship between the modules is summarised below. Any return values are stated in the description.

Parameters in the table are as follows:

• Par1 and Par3 are of type string.
• Par2 is of type integer.

(i) Identify the modules that would be implemented as functions.

(ii) Modules Mod-F and Mod-G are both called with Par3 as a parameter. In the case of Mod-F, the parameter is passed by value. In the case of Mod-G, the parameter is passed by reference.

Explain the effect of the two different ways of passing the parameter Par3.

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

The program analyses a student project and extracts information about each module that is defined (each procedure or function). This information is stored in a global 2D array ModInfo of type string.

A module header is the first line of a module definition and starts with either of the keywords PROCEDURE or FUNCTION.

An example of part of the array is given below. Row 10 of the array shows that a procedure header occurs on line 27 and row 11 shows that a function header occurs on line 35. "P" represents a procedure and "F" represents a function

The string stored in column 3 is called the module description. This is the module header without the keyword.

A valid module header will:

• be at least 13 characters long
• start with the keyword PROCEDURE or FUNCTION. The keyword may appear in either upper or lower case (or a mix of both) and must be followed by a space character.

The teacher has defined the first program module as follows:

Write pseudocode for module Header().

A global array is declared in pseudocode as follows:

DECLARE Data : ARRAY[1:150] OF STRING

A function TooMany() will:

1. take two parameters: • a string (the search string) • an integer (the maximum value)
2. count the number of strings in the array that exactly match the search string
3. return TRUE if the count is greater than the maximum value, otherwise will return FALSE

Write pseudocode for the function TooMany().

The pseudocode OUTPUT command starts each output on a new line.

A new procedure MyOutput() will take a string and a Boolean parameter. MyOutput() may be called repeatedly and will use concatenation to build a string using a global variable MyString, up to a maximum length of 255 characters.

MyString will be output in either of these two cases:

1. The Boolean parameter value is TRUE
2. The resulting string (after concatenation) would be longer than 255 characters.

If MyString is not output, the string is concatenated with MyString.

For example, the calls to MyOutput() given below would result in the output as shown:

MyOutput("Hello ", FALSE) MyOutput("ginger ", FALSE) MyOutput("cat", TRUE) MyOutput("How are you?", TRUE)

Resulting output:

Hello ginger cat How are you?

Notes:

• MyString is initialised to an empty string before MyOutput() is called for the first time.
• No string passed to MyOutput() will be longer than 255 characters.

Write pseudocode for MyOutput().

The design of the procedure given in part (a) is modified and MyString is changed from a global to a local variable declared in MyOutput().

When the modified procedure is converted into program code, it does not work as expected.

Explain why it does not work as expected.

A new module has been defined:

As a reminder, a message is defined as follows:

<STX><DestinationID><SourceID><Data><ETX>

Write pseudocode for module GetField().

A procedure Count() will:

1. input a value (all values will be positive integers)
2. count the number of odd values and count the number of even values
3. repeat from step 1 until the value input is 99
4. output the two count values, with a suitable message.

The value 99 must not be counted.

Write pseudocode for the procedure Count().

A procedure CreateFiles() will take two parameters:

• a string representing a file name
• an integer representing the number of files to be created.

The procedure will create the number of text files specified.

Each file is given a different name. Each file name is formed by concatenating the file name with a suffix based on the file number. The suffix is always three characters.

For example, the call CreateFiles("TestData", 3) would result in the creation of the three files, TestData.001, TestData.002 and TestData.003.

Each file will contain a single line. For example, file TestData.002 would contain the string:

This is File TestData.002

A module CheckFiles() will count the number of files produced by CreateFiles() in part (a).

CheckFiles() will take a string representing a file name and return the number of files found.

(i) Identify the type of module that should be used for CheckFiles().

(ii) Write the module header for CheckFiles().

A program contains six modules:

Module-X() calls Reset() Module-Y() calls Restore()

Copies of the same program will run on each computer. The program contains a global variable MyID of type string, which contains the unique ID of the computer in which the program is running.

When messages are received, they are placed on one of two stacks. Stack 1 is used for messages that have reached their destination and stack 2 is used for messages that will be forwarded on to another computer.

Additional modules are defined:

Write pseudocode for module ProcessMsg().

Module StackMsg() must be used.

A procedure RandList() will output a sequence of 25 random integers, where each integer is larger than the previous one.

Write pseudocode for procedure RandList().

A function TestNum() will take a six-digit string as a parameter.

The function will test whether the string meets certain conditions and will return an integer value as follows:

The function will return the highest possible value for the given string.

If the string does not meet any of the conditions, zero is returned.

Write pseudocode for function TestNum().

Assume that the parameter is valid.

A structure chart shows the modular structure of a program:

The structure chart shows that Sub-9() is a function.

A Boolean value is returned by Sub-9() for processing by Module-A().

The original parameter RA is of type integer and RB is of type string.

A record type MyType will be defined with three fields to store the values passed between the two modules.

The design is modified and Sub-9() is changed to a procedure.

The procedure will be called with a single parameter of type MyType.

Write the pseudocode header for procedure Sub-9().

A class of students are developing a program to send data between computers. Many computers are connected together to form a wired network. Serial ports are used to connect one computer to another.

Each computer:

• is assigned a unique three-digit ID
• has three ports, each identified by an integer value
• is connected to between one and three other computers.

Messages are sent between computers as a string of characters organised into fields as shown:

<STX><DestinationID><SourceID><Data><ETX>

For example, the following message contains the data "Hello Jack" being sent from computer "202" to computer "454":

<STX>"45420Hello Jack"<ETX>

Each computer will run a copy of the same program. Each program will contain a global variable MyID of type string which contains the unique ID of the computer in which the program is running.

The first two program modules are defined as follows:

Two new modules are defined, which will allow two users to exchange messages.

Reminders:

• Each program contains a global variable MyID of type string which contains the unique ID of the computer in which the program is running.
• Messages are sent between computers as a string of characters organised into fields as shown: <STX><DestinationID><SourceID><Data><ETX>

Write pseudocode for module Chat().

Modules GetData() and Transmit() must be used.

Module GetData() returns the data field from a message that has been received. If no message is available, the module waits until one has been received.

Explain the limitation of this on module Chat() from part (c).

Describe a modification to GetData() to address this limitation.

Limitation..........................................................................................................

Modification......................................................................................................

A library system gives every member an ID.

A valid ID meets all three of these rules:

• it is exactly 7 characters long
• the first 2 characters are upper-case letters in the range 'A' to 'Z'
• the last 5 characters represent a valid number

Write pseudocode for the function CheckID() that takes an ID as a parameter and returns TRUE if the ID is valid and FALSE if it is not.

You may use the built-in functions given in the insert.

A program controls the stock held in a warehouse.

The program contains the following procedure header.

Identify how each of the two parameters is passed.

A program keeps a running score for a player.

The program contains the procedure Update().

The main program is as follows.

The OUTPUT command starts each output on a new line.

State the three values that the program outputs, in the order in which they are output.

A program works out the total weight of the parcels loaded into a delivery van.

Line numbers are for reference only.

The programmer expects line 12 to output 23.

The program compiles with no errors, but line 12 outputs 0.

Explain why the program outputs 0, and state the change needed to the header at line 20 so that line 12 outputs 23.

A weather station program stores temperature readings in a text file.

The procedure SaveReading() has already been written. Its header is:

The procedure writes one reading to the file. It does not return a value.

At the station named Delta, a temperature of 21.5 degrees Celsius is recorded at hour 14.

Write the pseudocode statement that calls SaveReading() to store this reading.

A stock control program prints a label for each item that is placed on a shelf.

The program uses the procedure PrintLabel(). Its header is:

Explain the term procedure interface with reference to PrintLabel().

A global 1D array of integers contains four elements, which are assigned values as shown:

A procedure Adjust() changes the values stored in the array.

The procedure is written in pseudocode as follows:

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

A library program works out the fee a member owes when a book is returned late.

The function LateFee() is written in pseudocode as follows. Two lines are missing.

Complete the pseudocode by writing the two missing lines.

A hotel booking program needs a new module called StayCost().

The module is described as follows:

• it takes one parameter, an integer representing the number of nights of a stay
• it works out the total cost of the stay as a real value
• the total cost is needed inside a larger calculation in four different places in the program

Explain why StayCost() must be written as a function and not as a procedure.