辅导案例-H7126

  • June 1, 2020

Candidate Number H7126 THE UNIVERSITY OF SUSSEX BEng (final year) AND MEng (year 3) 2019 EXAMINATION Programming in C++ Assessment period: May/June 2019 (A2) DO NOT TURN OVER UNTIL INSTRUCTED TO BY THE LEAD INVIGILATOR Candidate should answer THREE out of FOUR questions Duration: 2 hours If all four questions are attempted, all will be marked, but the lowest mark will not be counted in the total for the paper. At the end of the examination the question paper and any answer books/answer sheets, used or unused, will be collected from you before you leave the examination room. Examination handout: None Please turn over H7126 Programming in C++ ___________________________________________________________________ 2 Question 1. a) Explain what is meant by the following terms: i) Class ii) Object Instance iii) Abstract class iv) Method overloading v) Method overriding [5 marks] b) What is the output of the following program? Explain your answer. voi d myf unct i on( i nt n, i nt &m) { n = 150; m = 250; } i nt mai n( ) { i nt n = 100; i nt m = 200; myf unct i on( n, m) ; cout < r et ur n 0; } [4 marks] c) Define the following types of error that may occur in a C++ program. In each case provide an example. i) Syntax error ii) Type error iii) Link error iv) Logic error [8 marks] d) Why is it better to use exceptions in C++ programming, rather than returning an error code? The user written function: myOpenFi l e( const st d: : st r i ng& name) throws the exception: st d: : r unt i me_er r or ( “ Coul d not open f i l e” ) . Write C++ code that will catch the exception and print the error message to the console when the function is called. [3 marks] H7126 Programming in C++ ___________________________________________________________________ 3 Question 2. a) The four basic features of object-oriented programming languages are said to be abstraction, polymorphism, encapsulation and inheritance. Define each of these terms. [6 marks] b) What is an abstract class and describe how one could be created in C++? [2 marks] c) There are three classes to design: ani mal , cat , and dog. To hold the height, each class has a protected field hei ght of type i nt . Each class also has a get and set methods. ani mal is an abstract class and cat and dog are concrete (i.e. not abstract) subclasses of ani mal . i) Using abstract concepts write these classes described above in C++. [9 marks] ii) Write a function that takes advantage of abstract classes to print the height of each cat and dog to the console. [3 marks] Question 3. a) What is the difference between a function declaration and a function definition? [3 marks] b) Consider the following partial class definition: c l ass Dat e { pr i vat e: i nt day; i nt mont h; i nt year ; publ i c: voi d advance( ) ; / / ot her code her e! } ; For simplicity, assume that all months have 31 days. i. Implement a constructor that takes no parameters and will initialise the date to 31st April 2019. [3 marks] ii. Implement the method advance( ) that will increase the date by one day. [4 marks] Question continued over H7126 Programming in C++ ___________________________________________________________________ 4 iii. Implement an overload of the default constructor so that the new constructor can take a user specified date. [2 marks] iv. If two date instances are compared we need to check that the year, month and day are both equal. Add a method to the class that could do this by overloading the == operator. [3 marks] c) A fully implemented class called Bi r t hday, that can store a birthday date has been written by a programmer. The programmer wants to now store the birthdays of their class mates. They initialise this storage with: Bi r t hday * b = new Bi r t hday[ 22] ; What are the potential pitfalls of this method? Suggest a better method that could be used when for example an extra person joins the class? [5 marks] H7126 Programming in C++ ___________________________________________________________________ 5 Question 4. a) A commonly used programming idiom is Resource Acquisition Is Initialization (RAII). i) What is the definition of RAII and what is the benefit of using it? [4 marks] ii) Why is better to use a smart pointer such as st d: : uni que_pt r to manage dynamically allocated memory rather than a plain C++ pointer? [4 marks] b) The following code shows a class example that reads some data and processes it. The code contents of r ead_dat a_f r om_f i l e have not been shown here but the comments describe what it does. i) What is the potential cause of a memory leak? [2 marks] ii) Suggest two ways in which this could be corrected. Explain why they work. [6 marks] c l ass ReadDat aExampl e { publ i c: i nt r eadDat a( i nt dat a_si ze) { i nt * dat a =new i nt [ dat a_si ze] ; i nt r es= r ead_dat a_f r om_f i l e( dat a) ; del et e [ ] dat a; r et ur n r es; } pr i vat e: i nt r ead_dat a_f r om_f i l e( i nt * dat a) { / * Thi s f unct i on, gener at es i nt eger dat a and st or es i t i n dat a. I t pr ocesses i t and r et ur ns t he r esul t as an i nt . I t may t hr ow an Except i on. * / … } } ; c) What does the const keyword mean? Give an example of its use in a method and explain why it is useful. [4 marks] END OF PAPER

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