CP1 Computing June 2007

[1]

Two different types of programming errors are syntax errors and logical errors. Explain each of these terms, giving one example in each case.

(i)

syntax error

[2]

an error in using the rules of the language
Eg. A spelling error 'PRUNT' instead of 'PRINT'

(ii)

logical error

[2]

the program runs but gives an incorrect result
Eg. Adding a discount amount instead of subtracting it from the total.

[2]

Data is held about the cars for sale at a car dealership.

In each case, name the most suitable data type for the storage of the following data:

(i)

the model name for the car, for example Fiesta;

[1]

string

(ii)

the number of doors, for example 4;

[1]

integer

(iii)

the average miles per gallon achieved by the car, for example 38.4;

[1]

real

(iv)

whether or not the car is new, for example TRUE;

[1]

boolean

(v)

a single letter code for whether the fuel used is petrol, diesel or other, for example P.

[1]

character

[3]

A systems analyst uses various methods to find out how an existing system works.
These include:

interviewing staff who use the current system
asking staff who use the current system to complete questionnaires

(i)

Describe one advantage of using interviews over questionnaires.

[1]

more flexible questioning. Questions can depend on responses to previous questions.

(ii)

Describe one advantage of using questionnaires over interviews.

[1]

many people can fill in questionnaires at the same time. An interview can only be held with one person at a time.

(iii)

The systems analyst may also find it useful to use the existing system or observe the existing system in use.

Describe one other method which the systems analyst can use to find out about an existing system.

[1]

any documentation about the existing system can be studied.

[4](a)

Computer programs need to be well documented.

State two types of documentation, in each case stating whom it would be written for.

[2]

User Documentation (Eg. Instructions for Use)
..for the user of the system
Maintenance Documentation
..for expert programmers and technicians.

(b)

Well written computer programs often contain different types of self-documentation.

Describe two types of self-documentation.

[2]

using meaningful identifier names
including plenty of descriptive comments in the program code

[5]

A taxi firm asks each driver to record the following information each time the taxi is hired:

the number of passengers using the taxi
the journey starting point, for instance Railway Station
the journey ending point, for instance Cardiff Road

The taxi firm then enters the data into a computer program.

(i)

A rogue value is used in this data.

(I) What is the purpose of a rogue value?

[1]

it indicates the end of a sequence of input data

(II) Which of the three data items being input in this case is most suitable for a rogue value?

[1]

the number of passengers

(III) Give a suitable rogue value in this case.

[1]

-1

(ii)

Name a data structure which could contain all three items of data for one journey as a single item.

[1]

a record

[6](a)

Using a clearly labelled diagram, explain how a binary search is used to locate an element in an array.

[3]

diagram must show the 'middle' data item is accessed
...and checked against the data item being searched for - discarding half the list
...and successively repeated.

(b)

Another type of search is the linear search.

(i)

State one situation in which it would be essential to use a linear search rather than a binary search.

[1]

if the data was not sorted, a linear search must be used.

(ii)

Give another situation in which either type of search could be used, but where it would probably be more sensible to use a linear search.

[1]

if the list was sorted but very small in number.

[7]

The secretary of a small social club makes use of an integrated package to communicate with the club's members.

(i)

Explain the term mail-merge and give an example to show how the secretary might use mail-merge.

[3]

a number of similar documents are created which use data fields
...that are merged in from a database (or spreadsheet)
Eg. Letters could be sent to all the members reminding them about subscriptions that are due, names and addresses are merged in from a database.

(ii)

The secretary sometimes uses a feature of the integrated package which allows a small set of instructions or keystrokes to be recorded for later use.

(I) What is the name given to this feature?

[1]

a macro

(II) Describe one way in which this set of instructions or keystrokes can be run.

[1]

the macro can be assigned to a combination of keys Eg CTRL M

(III) Give an example of how the secretary might make use of this feature.

[1]

a macro can be created for putting the club's letterhead at the top of a new document.

[8]

The river flowing through a certain city floods occasionally, causing widespread damage. The river authority monitors the water level in the river hourly, and when necessary issues either a standard warning or a high-priority warning. The data used include both the current river level and the increase in river level during the last hour.

The algorithm used is shown below:

1	input RiverLevel
2	input LevelIncreaseDuringLastHour
3	if ((RiverLevel > 12) OR ((RiverLevel > 8) AND (LevelIncreaseDuringLastHour > 3))
4	then output "High-Priority Warning"
5	else if((RiverLevel > 10) OR ((RiverLevel > 8) AND (LevelIncreaseDuringLastHour > 1)))
6	then output "Standard Warning"
7	else output "No Warning"

(a)(i)

State what the output will be when the inputs are:

RiverLevel = 13 Increase in river level during the last hour = 2

[1]

High Priority Warning

(ii)

State what the output will be when the inputs are:

RiverLevel = 9 Increase in river level during the last hour = 0

[1]

"No Warning"

(iii)

State what the output will be when the inputs are:

RiverLevel = 11 Increase in river level during the last hour = 0

[1]

"Standard Warning"

(iv)

State what the output will be when the inputs are:

RiverLevel = 7 Increase in river level during the last hour = 4

[1]

"No Warning"

(b)

The algorithm on the opposite page is correct. However, it is accidentally entered incorrectly, so that the word OR in line 5 is changed to AND

Line 5 now becomes:

5	else if((RiverLevel > 10) AND ((RiverLevel > 8) AND (LevelIncreaseDuringLastHour > 1)))

One of the parts (a)(i) to (iv) now gives a different output. State which part gives a different output and write down what the output will now be.

[2]

(iii) would give "No Warning"

[9]

A building firm buys items (such as windows and doors) from BuildRight, a local builders' merchant. BuildRight carry a large amount of stock. Sometimes, however, an item is out of stock at BuildRight, and staff at BuildRight then check if it is available from a national supplier.

The situation described is shown below:

(i)

What type of object does the following shape represent?

[1]

data store

(ii)

Give a suitable name for the object shown as a in the diagram.

[1]

stock details

(iii)

Give a suitable name for the object shown as b in the diagram.

[1]

BuildRight stock database

(iv)

Give a suitable name for the object shown as c in the diagram.

[1]

stock details

(v)

This type of diagram shows the flow of data in a computer system. Why is it important to show data flow?

[1]

the flow of data through a system is what a systems analyst deals with when designing a new computer system.

[10](a)

A certain programming language is very good at handling complex calculations.
Describe an application which could sensibly be written in this type of programming language.

[1]

Eg. an engineering program that allows complex calculations of stress in a building structure.

(b)

Describe one feature which it would be useful to have in a programming language used in a commercial application.

[1]

a record filing system ie. database

(c)

Many computer programs use iteration. What is meant by the term iteration?

[1]

repetition of a section of program code

(d)

Explain the difference between a global variable and a local variable.

[2]

global variables exist and are usable all through a program
local variables can only be used inside the subroutine in which they are declared

(e)

Describe the function of a translation program when applied to a source program.

[1]

it converts the source program into an executable machine code program.

[11]

In the following question, additional credit (up to 3 marks) will be gained if your answer demonstrates skill in written communication.

When a new computer system is being developed, the designers need to take into account a number of issues.

One of these issues is maintenance. It is very important that the programs in the new computer system can be maintained. Describe in detail the different types of program maintenance which may be necessary, giving an example in each case.

Another issue is the human computer interface (HCI) which needs to be suitable for both experienced and novice users. It should be accessible to people with physical handicaps. Describe in detail what features you would expect to find in a well designed HCI.

[9+3]

Perfective maintenance is carried out on a system to try to improve it. An example would be re-writing a program to make it run faster.

Corrective maintenance would be needed to correct any problems in the system, such as programs that crash under certain circumstances.

Adaptive maintenance would involve changing a system to meet the changing circumstances of the business, such as opening new branches.

In order for the HCI to be usable by novice users, an intuitive and user-friendly method of selecting and running applications would be needed such as a GUI - a graphical user interface that uses a mouse pointer to click on small icons representing applications.

A command line interface may be optional for expert users where complex commands can be entered, or batch programs that run a sequence of instructions.

People with physical handicaps may need speech interface, where commands can be spoken into a microphone.