Advances in Programming Languages: Exam preparation and exam questions

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1 Advances in Programming Languages: Exam preparation and exam questions Stephen Gilmore The University of Edinburgh March 24, 2006 Examinations What is the purpose of examinations? 1. To test understanding. 2. To test knowledge. 3. To complement coursework. Preparing for examinations There are many types of revision for examinations. 1. Studying lecture notes. 2. Trying past exam papers. 3. Coding example programs. Should vary the type of revision to retain interest. Generally bad ideas 1. Question spotting. 2. Leaving all revision to the night before. 3. Trying to sneak notes into the exam. 4. Staying up all night revising. 5. Popping beta-blockers like M&Ms Generally good ideas 1. Planning ahead. Assign blocks of time to courses, including the courses you don t like. 2. Revising with others. No concept of plagiarism in revision. 1

2 UG4 Advances in Programming Languages 2005/ Trying not to get too stressed. Take exercise. Take breaks. 4. Trying not to have unrealistic expectations. Unlikely to get first class marks in every subject. Keep perspective. Format of examinations Honours examinations are 1hour and 45minutes duration. Some examinations any two questions from three. (e.g. APL) Some examinations have compulsory questions. Consult the rubric! Can use 15 minutes for reading and thinking and then have 45 minutes for each question. Types of exam question Examination questions are of different types. Testing knowledge. Testing understanding. Based on extrapolation. Applying skills. Based on scenarios. Structured/unstructured. Good/bad. Types of exam question: testing knowledge Questions of this type ask you if you know a fact, or a definition, or a description. Explain the concept of definite assignment in Java. [1 mark] Try to give the definition as precisely as you can. Characterise generally if you cannot remember precisely. A sample answer to the above is shown below. Example answer: Java s concept of definite assignment is that each variable must be defined on all paths which lead to a use of that variable. This prevents uninitialised variable errors which are common from languages such as C, and supports compile-time type-checking of programs.

3 UG4 Advances in Programming Languages 2005/ Types of examination question: descriptive Rather than just asking you to recall a particular definition, some questions ask you to give examples. (b). Name three types of pointers which are provided by the Cyclone language. Explain the use of each, illustrating your answer with fragments of Cyclone code showing how these pointers are declared and used. Types of examination question: extrapolation Some questions, or some parts of questions, ask you to consider a problem which goes (slightly) beyond the material covered in the course lectures. A use of such questions is testing reasoning skills. You won t just know the answer, but you may be able to work it out from things which you know already. Explain your reasoning, because even if you get the answer wrong, you may display insight in the reasoning. (c). The following Cyclone function is faulted at compile time. int* makecounter() { int counter = 0; return &counter; } If the return statement is changed to return (int* H) &counter; will the compilation succeed? Explain the problem and the attempt at repairing it. The cast will not succeed. Cyclone says Cannot cast int * makecounter to int *. H and makecounter are not compatible. It would be possible to make an educated guess at this answer by reasoning that (i) this function is broken, and should not type check; (ii) Cyclone is strongly-typed, and statically type-checked (so if it is going to find a type-error in a program it must do so at compile-time); (iii) Cyclone will not pass casts just because the data is the same size; and (iv) Stephen always says casts are a bad idea. Types of examination question: application Some examination questions ask you to apply skills which you have learned to a problem. This can include deducing something about a program or writing a program to solve a problem. (e). What is the type of the following O Caml function, fix? let rec fix f = function x > f (fix f) x;;

4 UG4 Advances in Programming Languages 2005/ (This is a rather poor example because it is a rather tricky function.) O Caml says fix : -> b) -> a -> b) -> a -> b (( a (f). Consider the following O Caml program. type colour = Red Green Blue;; let brighter (c1, c2) = match (c1, c2) with (Red, ) > true (Green, Red) > false (, Blue) > true;; Will this program compile without warnings? Rewrite it in Java using the features of Java 1.5. [7 marks] O Caml says Warning: this pattern-matching is not exhaustive. Here is an example of a value that is not matched: (Blue, (Green Red)). A Java version should use enumerations and rewrite the pattern matching using switches. Types of examination question: scenarios Some examination questions relate material from the course to real world scenarios. Your answer should relate to the question. Don t just write down everything which you know. (g). Harry Håaker of Advanced Software Ltd. argues that mobile code must be untyped because the server cannot know in advance the types of data values which the client will need. Would you agree with Harry s argument? [12 marks] As a general guideline, whatever Harry Håaker says, it must be wrong. Further, type checking of programs has been identified in the course as an advance in programming languages. Mobile code (as in Java) can be strongly typed but some of the type checking is done dynamically, at run-time (as in Java). Types of examination question: unstructured Unstructured questions are poor style on examination papers. These show that the lecturer has been too lazy or too dull to think up an interesting question. 1. Are Java s generics useful? Discuss. [25 marks] If you have one of these on one of your examination papers just write everything you know.

5 UG4 Advances in Programming Languages 2005/ Types of examination question: bad Questions which rely too much on picky details of language syntax (such as the precedence and associativity of operators) would be unhelpful. An examination should be about substance, not detail. 2 (a). What is the type of the following O Caml function? fun ( R, S, (+.) :: l as h :: t) > l Types of examination question: ambiguous/unclear [12 marks] Before examination papers are ever seen by students, a scrutiny meeting looks for errors and ambiguities. After this, the external examiner looks for errors and ambiguities. Still, sometimes, some remain. (b). What is the most efficient/safe program development form? [13 marks] If you have one of these on one of your examination papers then you can ask the invigilator during the examination to find out what the question is meant to mean. They will telephone the course lecturer and relay your question to them and their answer back to you (or make an announcement to the hall). After your examination, you should complain to your course organiser, the chair of the Board of Examiners, and the Director of Teaching. This is Should Never Happen world. Things to remember Attempt past papers early, so that you can work out in advance whether you need to do more studying for a course. Find past examination papers on the ITO Web pages. Find specimen examination paper on course Web pages. Study with other people. You can t take a calculator into an exam.