| (a) | Identify the differences between call-by-value
and call-by-reference parameter passing.
|
[2] |
| (b) | This question is concerned with the
implementation of routines that analyses a simple examination "pass mark"
database. The database can contain at most ClassSize records. The various database types you should use in your routines are
shown below. Const ClassSize
= 20;
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|
(i) Define a function averageMark that takes two arguments: a pass mark
database; and an integer n (you can assume that n  ClassSize) that identifies that the first n elements in the database contain student marks. The result from the function
should be a Real that represents the
average mark of the first n elements.
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[5] | |
| (ii) Define a procedure markBand that takes as its arguments a database
of marks and an integer n (you can
assume that n ClassSize) that identifies the number of pass
marks in the database, and returns two results: the lower mark of a candidate in the
examination; and the highest mark (remember to define a procedure and not a function).
|
[6] | |
| (iii) The designer of the database would like to
know may many "no-shows" there were for an examination. The designer decides to
use the DatabaseType representation
of a database, and uses a pass mark of zero to represent a no-show in the examination.
Explain why this solution is problematic, and describe the effect on the two functions averageMark and markBand.
|
[3] | |
| (iv) Define a representation for the DatabaseType that provides a satisfactory
solution to the no-show problem.
|
[1] | |
| (v) Using your new definition of DatabaseType, define a function candidates that takes as its arguments a database of marks, and returns the number of students who attempted the examination. | [3] |