CP1 Computing Jan 2001

1(a)

A program team is developing a suite of programs. Frequently, they need to deal with syntax errors, execution errors and logical errors. In each case, explain the term and give an example.

(i)

syntax error

[2]

An error in using the rules of the language which causes failure to compile.
Eg Mis-spelling a command

(ii)

execution error

[2]

An error which occurs when the program is run.
Eg If an unusual item of data is entered and the program crashes.

(iii)

logical error

[2]

The program runs but does not do the right thing - ie an error in the design of the program.
Eg An incorrect mathematical formula may have been used.

(b)

Why is it generally easier to find syntax errors than logical errors?

[1]

The compiler will detect syntax errors and stop the compilation process and output a diagnostic error message.

2(a)

Character,string and boolean are names of simple data types.

(i)

Give an example of data which could be held in the character type.

[1]

Eg A code letter eg 'M' or 'F' for a sex field.

(ii)

Give an example of data which could be held in the string type.

[1]

Eg A name

(iii)

Give an example of data which could be held in the boolean type.

[1]

Eg A field indicating whether a house has a garage or not (True or False)

(b)

There are at least two numerical data types. What numerical data type is best suited to storing:

(i) the number of elements in an array

[1]

Integer

(ii) the temperature of a liquid in a scientific experiment?

[1]

A real number

A binary search is used in certain circumstances to attempt to find an element in an array.

(i)

State the major advantage of a binary search over a linear search.

[1]

It is much faster to find data.

(ii)

A binary search cannot always be used. In what circumstances is it not suitable to use a binary search?

[1]

If the data is not sorted, a binary seacrh will not work

(iii)

It can be shown that, for a binary search, it takes around 14 steps to search for an element in an array of 10000 items. Assuming this is true, what would be the corresponding figure for an array of 20000 items?

[1]

15 steps (After one step the data to be searched is halved ie down to 10000 items)

Different programming languages are used in different application areas.

(i)

Certain programming languages are used for commercial applications, while others are used for scientific applications. Describe one feature which it would be useful to have in each of the following:

I. a language used in a commercial application;

[1]

File-handling commands eg Searching and sorting

II. a language used in a scientific application.

[1]

High-precision calculations eg Trigonometrical function

(ii)

Hypertext mark-up language (HTML) is an example of a language which is used to produce web pages. Explain why this type of language is suitable for this application.

[2]

Fomatting information is contained in the page so it can be used on different browsers
Links can be inserted to other web pages

(iii)

A source code program is often input to a translation program. Explain the two terms:

I. source code program

[1]

The (text) program as written by the programmer using a programming language.

II. translation program

[1]

A program (assembler, compiler, interpreter) which converts the souce code program into a program which the computer can execute. (machine code)

An office worker uses a computer package which contains a word processor and a spreadsheet.

(a)

There are benefits and drawbacks of using an integrated package of this type compared with using separate word processing and spreadsheet packages.

(i) Describe two benefits of the integrated approach;

[2]

the user can get used to a common interface
easier to copy./move data between the packages.

(ii) Describe one drawback of the integrated approach.

[1]

it will use more memory when running or storage space on a disk.

(b)

The worker frequently uses the following features:

header/footer
mail merge
macro

Explain each of these terms. In each case, give an example of the use the office worker might make of the feature.

[6]

header is a piece of text which appears on the top of every page of a document. A footer appears at the bottom of every page of a document.
Eg : Title of a document in the header and page numbers in the footer.
mail merge - using data from a database on form letters to produce a number of similar documents.
Eg A personalised letter to all the customers informing them of a new address.
macro - a command which consists of a number of stored instructions.
Eg On a spreadsheet, a macro could set the background and foreground colors and the font characteristics for a selected cell.

Records and two-dimensional arrays are examples of data structures which a manufacturing company uses to store information about its sales staff and their sales.

(i)

Give a detailed example of sales staff information which might be stored in the form of records, and state why this data structure is suitable in this case.

[2]

Staff ID number - integer
Staff name - string
Department - character

The details of each member of staff would be stored as a record of the above type. This data structure is suitable because there is data od different types in each record.

(ii)

Give a detailed example of sales information which might be stored in the form of two-dimensional arrays, and state why this data structure is suitable in this case.

[2]

The number of sales each member of staff had made in each month of a year would be stored as a two-dimensional array.

This data is suitable because all the data is of the same type (integer).

The following algorithm is intended to output the maximum value in an array of positive integers. The array is called cost and has n values from cost[1] to cost[n].

set max := cost[1];
set pos := 1;
for count := 2 to n
    if cost[count] > max
        then
            set max := cost[count]
            set pos := count;
    endif;
next count;

output (max, pos)

(i) What other item of information does the algorithm output?

[1]

The position of the maximum value.

(ii) What will happen if the array contains two or more equal values?

[2]

The maximum value will be output together with the position of the first integer with that value.

(iii) The loop in this algorithm is controlled by the variable count. An alternative method of controlling a loop would be by the use of a rogue value. Give an example of a suitable rogue value in this case and state where the rogue value should have been placed in the data.

[2]

A suitable rogue value would be -1 (since all the integers are positive)

The rogue value must be placed at the end of the data so it is the last one to be input. ie at cost[n+1]

After an electricity meter reader has visited a number of customers' homes, he or she inputs all the data into the company's computer system. In each case, a check is then made that the current meter reading is not far too large or far too small compared with the reading taken six months ago, which would suggest an error had been made. If this check is satisfactory, the new figure is included in the data held for each customer.

The situation described so far is shown in the diagram below:

(i) Write down the name for this type of diagram.

[1]

A data flow diagram.

(ii) Describe why this type of diagram is particularly useful to systems analysts.

[1]

It shows the flow of data through a system in an easy-to-understand way.

(iii) What type of object does the open box symbol in the diagram represent?

[1]

A data store

(iv) Give a suitable name for this object (shown as a)

[1]

Customer's previous readings.

(v) What type of object does the arrow symbol in the diagram represent?

[1]

data flow

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

[1]

previous meter reading

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

[1]

current meter reading

9(a)

A small shop still uses a paper-based system to control its stock flow. Imagine that you are asked to carry out a systems analysis and design for a new computer-based system for stock flow.

The new system must support the following operations:

maintain records of all the stock
maintain records of all sales

As systems analyst, you will need to carry out a number of tasks.
Making any reasonable assumptions you wish about the existing paper-based system, describe each of the following tasks in detail, making it clear how you would carry out each task in this case.

(i) feasibility study

[2]

a study to see if a new computer system is worth having. Costs of installing and training would need to be weighed against the predicted benefits of the system.

(ii) analysis of the existing system

[2]

interviews of staff and management
questionnaires to staff and customers
observation of current practice (who does what)
reading existing documentation

(iii) data validation

[2]

Tests will need to be carried out on data before it is input to the system to see if the data is reasonable...eg type checks, range checks, check digits etc

(iv) design of the user interface

[2]

decide on the hardware needed eg mouse, keyboard, touch-sensitive screens etc
decide on type of interface - menu, command line or GUI
design the layout of the screen displays.

(b)

When a new system is implemented, there is usually a changeover period.

(i) Explain the term changeover

[1]

Moving from the old system to the new system.

(ii) Why is it useful that the old system should still be available?

[1]

In case the new system fails to work properly.

(c)

After a computer system is developed, there are often post-implementation costs. Give two examples of post-implementation costs and state in each case how the cost can be minimised.

[4]

extra features may be added to the system which were not thought of at the design stage.
- A more thorough consideration of requirements at the design stage.
problems may arise which will need to be fixed.
- A careful testing of the system would be needed before it is put into operation.

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

A company wishes to undertake a substantial software development. Software is normally written in the form of modules. This approach often makes use of standard modules and most programmers use some form of self-documenting code.

Describe in detail why it is useful to organise a program into modules and explain what is meant by the term standard module, giving one example of a task which might be carries out by a standard module. Also explain two advantages of using standard modules.

Explain why it is sensible to use self-documenting code, giving two different examples.

[7+3]

Large programs should be broken down into small self-contained modules. These are easier for the programmer to analyse, design, code and then test. A number of different programmers may be assigned to different modules, coding and testing each one separately before putting them together in the final program.

A standard module consists of a number of previously coded subroutines. For example, a standard module may consist of a number of routines used to validate input data. These have already been thoroughly tested and programmers will save time by including these in their programs.

Self-documenting code should be used where there are a number of comments included in the program explaining each section. This is useful for future programmers who may have to maintain the program. Another method of self-documentation would be to use sensibe variable names in the source code.