File Processing & Exception Handling (Cambridge (CIE) A Level Computer Science): Exam Questions

A program is being developed to implement a game for up to six players.

During the game, each player assembles a team of characters. At the start of the game there are 45 characters available.

Each character has four attributes, as follows:

The programmer has defined a record type to define each character.

A new module will store the contents of the Character array in a text file.

The module is defined as follows:

Complete the pseudocode for module Save().

PROCEDURE Save()

The program is changed and the record type definition is modified as follows:

TYPE CharacterType

DECLARE Player : INTEGER

DECLARE Role : STRING

DECLARE Name : STRING

DECLARE Level : INTEGER

DECLARE Status : BOOLEAN

ENDTYPE

Describe how the additional Boolean field may be stored with the rest of the fields on one line of a text file.

The Character array data has been saved in the text file SaveFile.txt Each line of the file contains one element of the array (one record).

New modules are defined:

As a reminder, the record structure is repeated here:

TYPE CharacterType

DECLARE Player : INTEGER //Field number 1

DECLARE Role : STRING //Field number 2

DECLARE Name : STRING //Field number 3

DECLARE SkillLevel : INTEGER //Field number 4

ENDTYPE

Write pseudocode for module Restore().

You must use the module Extract().

The game can last for several days and users often find that they have to close and rerun the game program many times in order to complete it.

Describe the benefit of using the file SaveFile.txt as described above.

A second module is defined:

Write pseudocode for module Stage_1().

Module DeleteComment() must be used in your solution

Two modules are defined:

Write pseudocode for module Stage_2(). Modules DeleteComment() and DeleteSpaces() must be used in your solution.

A program uses a global 1D array of type string and a text file.

An algorithm that forms part of the program is expressed as follows:

• copy the first line from the file into the first element of the array

• copy the second line from the file into the second element of the array

• continue until all lines in the file have been copied into the array

Stepwise refinement is applied to the algorithm.

Outline five steps for this algorithm that could be used to produce pseudocode.

Assume there are more elements in the array than lines in the file.

Do not use pseudocode statements in your answer.

Step 1 ...............................................

Step 2 ...........................................

Step 3 ............................................

Step 4 ................................................

Step 5 ................................................

A new module is required:

As a reminder, the previous example of part of the array is repeated below:

Write pseudocode for module FindModules().

Assume that the array contains enough rows for the number of modules in each project.

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 Kevin" being sent from computer "101" to computer "232":

<STX>"232101Hello Kevin"<ETX>

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

The programmer has defined the first two program modules as follows:

Write pseudocode for module SendFile().

Assume:

• module Transmit() has already been written and is used to transmit a message

• the value of MyID may be used as SourceID

• the file specified contains no blank lines

• e file specified does not contain the line "****"

Module SendFile() is used to copy a file from one computer to another.

A module within the program running on the destination computer will receive the data and write it to a new file.

Explain why module SendFile() transmits the message with data string "****" after the last line of the file.

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

Write pseudocode for CreateFiles().

Assume both parameters are valid and that the integer value is between 1 and 999, inclusive.

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.

State the file mode that should be used in CheckFiles().

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> "454202Hello 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:

Write pseudocode for module ReceiveFile().

Module GetData() has already been written and must be used.

The use of the string "****" as explained in the module description for ReceiveFile() may cause a problem.

Explain the problem and suggest a solution.

Problem .....................................................

Solution ........................................................

A pseudocode algorithm finds a customer account record in a random file and outputs it. The records are stored using the user-defined data type TAccount.

TYPE TAccount

DECLARE AccountNumber : INTEGER

DECLARE LastName : STRING

DECLARE FirstName : STRING

DECLARE Address : STRING

DECLARE ContactNumber : STRING

ENDTYPE

Complete the file handling pseudocode.

The function Hash() takes the customer account number as a parameter, calculates and returns the hash value.

DECLARE Customer : TAccount

DECLARE Location : INTEGER

DECLARE AccountFile : STRING

.................................................................................................. $\leftarrow$"AccountRecords.dat"

............................................................... AccountFile ..........................................................

OUTPUT "Please enter an account number"

INPUT Customer.AccountNumber

Location $\leftarrow$ Hash( .............................................................................................................. )

SEEK ..................................................................................................................... , Location

............................................................. AccountFile, ..........................................................

OUTPUT Customer // output customer record

CLOSEFILE AccountFile

Define the term exception handling.

State two possible causes of an exception.

Describe, with an example, what is meant by an exception.

A pseudocode algorithm searches for a customer record in a random file AccountRecord.dat. A user inputs the name of the customer.

The records are stored using the user‑defined data type TAccount.

TYPE TAccount

DECLARE AccountNumber : INTEGER

DECLARE Name : STRING

DECLARE Address : STRING

DECLARE Telephone : STRING

ENDTYPE

If the record is found, it is output, otherwise an error message is displayed.

Complete the file handling pseudocode.

DECLARE Customer : TAccount

DECLARE Location : INTEGER

DECLARE MaxSize : INTEGER

DECLARE FoundFlag : BOOLEAN

DECLARE SearchCustomer : STRING

MaxSize $\leftarrow$1000

OPENFILE ...............................................................................................................

Location $\leftarrow$ 1

............................................................................................................... $\leftarrow$ FALSE

OUTPUT "Enter the customer’s name"

...............................................................................................................

................................................................................... AND Location <= MaxSize

................................... "AccountRecord.dat", ............................................

GETRECORD "AccountRecord.dat", Customer

IF SearchCustomer = Customer.Name THEN

OUTPUT "Customer found: "

OUTPUT Customer // output customer record

FoundFlag $\leftarrow$ TRUE

ENDIF

Location $\leftarrow$ Location + 1

ENDWHILE

IF NOT FoundFlag THEN

OUTPUT ".........................................................................................................."

ENDIF