###2S####2o####2o###3a#x##23####3# 7###########################4a######"#######A##################0####0####1####1####1####1#X##23####23####23####2C# ##3####47#*##4a####1########47####4##&##47####47####4a####47####47####47####47### #47####47####Answer 3 questions.Time allowed: 1.5 hoursDisclaimer:This sample paper gives an indication as to the style of the sort of questions that may appear on the CS213 examination, i.e. giving a reasonable indication of the mix of bookwork and problems.It should not be interpreted as indicating that certain topics will appear or will not appear on the paper. Potentially questions may be set on any part of the lecture material. Any deductions that you make from this sample paper regarding the topics appearing in the actual examination, you make at your own peril!1. a) Say what is meant by the terms expression and command, bringing out as clearly as possible the distinction between the two terms. Your answer should introduce the concept of state. Discuss the extent to which programming languages in current use maintain a clear separation between expressions and commands. Credit will be given for relevant examples and for comment on the advantages and disadvantages of separation of expressions and commands.(9 marks) b) Outline the similarities and differences between the switch statement in languages such as C and Java and the CASE statement in Ada. In your answer you should concentrate mainly on the semantics of the two constructs rather than their syntactic differences and you should comment on the advantages and disadvantages from a software engineering point of view of the two constructs.. (8 marks) c) Describe what is meant by i) static scoping ii) dynamic scoping in a computer language. Illustrate your answer with a suitable example code fragment.(8 marks)
2. a) Explain what is meant by the following terms relating to subprogram parameters: i) a value parameter (3 marks) ii) a reference parameter. (3 marks) Discuss briefly the parameter-passing methods used in Ada for IN mode parameters distinguishing clearly between the methods used for scalar types, composite types and tagged types.(3 marks) b) An unconstrained type Vector is defined in Ada as follows:TYPE Vector IS ARRAY(Positive RANGE <>) OF Float; Define new overloadings for the Ada operators "+" and "*"; the operator "+" should add two vectors of the same size whilst the operator "*" should allow multiplication of a vector of type Vector by a scalar of type Float.(7 marks) c) State what is meant by aliasing in a computer language. (3 marks) Consider the following code which defines a multiplication procedure for 3-dimensional vectors of the type Vector defined in part (b):SUBTYPE Vec3 IS Vectotr(1 .. 3);PROCEDURE VectorProduct(A, B : IN Vec3; C : OUT Vec3) ISBEGIN C(1) := A(2)*B(3) - A(3)*B(2); C(2) := A(3)*B(1) A(1)*B(3); C(3) := A(1)*B(2) - A(2)*B(1);END VectorProduct; Discuss carefully any potential pitfalls that might arise when using the procedure VectorProduct and outline how the subprogram might be recoded to avoid these pitfalls (full Ada code is not necessary).(6 marks)
3. Consider the following task type Timer, which provides for a time display that counts down in seconds until a time allowance has expired. For simplicity, code for controlling the screen position at which output is produced has been omitted.TASK TYPE Timer IS ENTRY Start(From : in Natural); ENTRY Check(NoTime : out Boolean); ENTRY Stop;END;TASK BODY Timer IS StartTime, Now : Duration; -Used with Split and Clock from Ada.Calendar Year, Month, Day : Integer; -- Needed to use Split TimeGone, TimeRecorded : Integer := 0; TimeLeft : Integer;BEGIN ACCEPT Start(From : in Natural) DO TimeLeft := From; END; Split(Clock, Year, Month, Day, StartTime); Put("Time Left: "); Put(TimeLeft, 2); LOOP SELECT ACCEPT Stop; EXIT; OR ACCEPT Check(NoTime : out Boolean) DO NoTime := TimeLeft <= 0; END; OR DELAY 0.1; IF TimeLeft > 0 THEN Split(Clock, Year, Month, Day, Now); TimeGone := Integer(Now - StartTime); IF TimeGone > TimeRecorded THEN TimeLeft := TimeLeft - (TimeGone TimeRecorded); TimeRecorded := TimeGone; Put(TimeLeft, 2); END IF; END IF; IF TimeLeft <= 0 THEN Put(ASCII.BEL); END IF; END SELECT; END LOOP;END; a) Show how to code a program, making appropriate use of Timer, that asks a question to which the user must respond in a set time. Give suitable declarations and a main program. Cursor positioning code may be omitted.(8 marks) b) Explain the structure of the Timer code, concentrating on those aspects that are specific to concurrent programming, for example the SELECT statement.(9 marks) c) Explain how the code that you gave for part (a) makes use of Timer. Pay particular attention to communication.(8 marks)
4. a) Describe briefly the purpose of protected objects in Ada and outline the r5les of procedures, functions and entries provided in the visible part of a protected object's specification.(10 marks) b) The following protected type Stack encapsulates stack of integer values based on a linked list implementation: PROTECTED TYPE Stack IS ENTRY Push(X : IN Integer); -- push item X onto the top of the stack ENTRY Pop(X : OUT Integer); -- pop an item off the top of the stack FUNCTION IsEmpty RETURN Boolean; -- returns True if the stack is empty and False otherwise PROCEDURE Clear; -- resets the stack to emptyPRIVATE TYPE Node; TYPE Ptr IS ACCESS Node; TheStack : Ptr;END Stack; Write a suitable body for the protected type Stack. Storage deallocation is not required. (13 marks)
5. a) Describe briefly the purpose of controlled types in Ada and outline the r les of the three primitive operations Initialize, Finalize and Adjust of controlled types.(6 marks) b) Outline the steps necessary to define a new controlled type in Ada highlighting the rTles of the package Ada.Finalization, type extension, primitive operations and abstract types in the process.(7 marks) c) The following outline package specification provides a type List for a singly-linked list of integers by extending the type Controlled from Ada.Finalization. The features of controlled types are to be used to provide automatic storage deallocation and deep copy on assignment of list objects and automatic storage deallocation when control finally leaves the scope of a list object.WITH Ada.Finalization; USE Ada.Finalization;PACKAGE SL_List IS TYPE List IS NEW Controlled WITH .... PRIVATE; -- declarations of exported operations for the type List ....PRIVATE TYPE Node; TYPE NodePtr IS ACCESS Node; TYPE Node IS RECORD ..... -- to be completed END RECORD; TYPE List IS ......; -- to be completed PROCEDURE Initialize(L : IN OUT List); PROCEDURE Finalize(L : IN OUT List); PROCEDURE Adjust(L : IN OUT List);END SL_List; Complete the private part of the package specification where indicated and write suitable implementations for the operations Initialize, Finalize and Adjust.(12 marks)END OF EXAMINATION PAPER
Extra question for good measure!6 a) Describe briefly the meaning of the following generic formal parameter specificationsi) TYPE T IS PRIVATE;ii) TYPE T(<>) IS PRIVATE;iii) TYPE T IS LIMITED PRIVATE;iv) TYPE T IS (<>);v) TYPE T IS RANGE <>;vi) WITH FUNCTION "+"(X, Y : T) RETURN T;(9 marks) b) The following is an outline declaration of a generic function Max which is to return the largest element of an array of type Collection according to some comparison function "<" which is to be supplied as a generic parameter when the function is instantiated. In an instantiation of the function the actual parameter corresponding to formal parameter Collection can be any (constrained or unconstrained) array of elements of any non-limited definite type indexed by any integer type.GENERIC TYPE ElemType IS .....; -- to be completed TYPE IndexType IS .....; -- to be completed TYPE Collection IS ARRAY .....; -- to be completed WITH FUNCTION "<" .....; -- to be completedFUNCTION Max(C : Collection) RETURN ElemType; Complete the declaration of the function and write a suitable complete function definition.(11 marks) c) Write down suitable code fragments to instantiate the generic function Max in (b) above i) to return the largest element in an unconstrained array of integer values indexed by the enumeration type DayOfWeek whereTYPE DayOfWeek IS (Mon, Tue, Wed, Thu, Fri, Sat, Sun);(2 marks) ii) to return the record with the smallest Key field in a constrained array of record values of type RecType indexed by the integer subrange MonthNumber whereTYPE RecType IS RECORD Key : Integer; -- other fields of the recordEND RECORD;SUBTYPE MonthNumber IS Integer RANGE 1 .. 12;(3 marks)CS213 Programming Language Concepts and Paradigms Page # of 5# 9#hh are each #######,######8###;###<###c###m###r###y#########J###P### ##################5###7###### ## b## e## ## ## ## ## ### ### 0## 8## ## ##
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