University of Cape Town Department of Computer Science. Computer Science CSC115F. June Exam 2002

Transcription

1 University of Cape Town Department of Computer Science Computer Science CSC115F June Exam 2002 Marks: 100 Time: 3 Hours Surname NAME: STUDENT NO: Approximate marks per question are shown in brackets The use of calculators is permitted Initials COURSE CODE: CSC This paper consists of 24 questions and 18 pages (including this cover page). Mark Allocation Quest Marks Internal External Quest Marks Internal External 1 [5] 13 [2] 2 [3] 14 [5] 3 [4] 15 [6] 4 [5] 16 [4] 5 [5] 17 [5] 6 [5] 18 [5] 7 [2] 19 [5] 8 [2] 20 [5] 9 [4] 21 [7] 10 [2] 22 [3] 11 [4] 23 [6] 12 [4] 24 [6] Total Total Grand Total Final Mark Internal Examiner: External Examiner: 1

2 Question 1. Section 1. Programming Basics [5 marks] Explain the following computing concepts in your own words, give examples where appropriate. a) Primary memory. b) high level language. [1] c) Abstraction. [1] d) A compiler. [1] e) An algorithm. [1] [1] 2

3 Question 2. [3 marks] a) What does the following program produce? // The "DisplayAverage" class. public class DisplayAverage public static void main (String[] args) int firstnum=10; int secondnum=12; int thirdnum=15; int fourthnum=18; double average; average=(firstnum + secondnum+ thirdnum+fourthnum)/4; System.out.println("The average is " + average); // main method // DisplayAverage class b) What is the simple remedy? [2] [1] 3

4 Question 3. [4 marks] Imagine a programmer is writing a class using the Turtle class and finds that he needs to slow the Turtle down so that users can see how a shape is drawn. The programmer decides to use pause in the following manner: SmartTurtle myturtle = new SmartTurtle(); myturtle.move(50); myturtle.turnright(30); myturtle.pause(100) myturtle.move(50); myturtle.turnright(30); myturtle.pause(100); etc. Show how such a method would be added to the SmartTurtle class. (Hint looping for a large number of iterations doing nothing wastes time). Question 4. [5 marks] The following shape is produced by repeatedly drawing a pentagon and turning through some angle. [4] Write a Java class RotatedPentagon that will produce this shape using the Turtle class. The Turtle instruction set: Move() // Moves the Turtle. If the pen is down leave a line. TurnRight( ) // Turns the turtle to the right. Max turn is 180 degrees. 4

5 PenUp( ) // Picks up the Turtle pen. PenDown( ) // Puts down the Turtle pen. IsPenDown( ) // Returns true or false depending on the state of the Turtle. You are given the first part of the program. Complete this by adding the statements that are missing and then add the rest of the program. // This program draws a pentagon and spins it 10 times. ; public class RotatedPentagon public static void main (String [] args) throws TurtleException Turtle aturtle = ; // set up the parameters for the shape add the // number of sides and number of shapes to be // drawn. int numsides = ; int size = 200; int numshapes = ; int angle = ; [5] 5

6 Question 5. [5 marks] Write a java - turtle class to draw the following shape: The size of each square is 100 turtle steps. Make your program as efficient as possible. Question 6. [5 marks] The distance between two points (x1, y1) and (x2, y2) on a plane, is given by the formula v = (x2 - x1)/2 + (y2 - y1)/2. Write a Java method, that takes 4 parameters, called distance i.e. distance(int x1, int y1, int x2, int y2) and returns the distance between the two points (as a double). [5] [5] 6

7 Question 7. Section 2. Java Basics and Number Systems [2 marks] What Java command would you use to print out the following text on the console: The Quick Brown Fox said hello! [2] Question 8. [2 marks] Identify two errors in the following Java class definition class BrokenClass public static void main(void) System.out.println("it s broken!"); Question 9. [4 marks] a) Explain why we need a type casting operator in Java, and give an example of using such an operation to convert an integer to a byte. [2] b) What will the variable x contain after this expression has been evaluated by Java: int x = 1.2*3 - (5/2*3)*2.1 [2] [2] 7

8 Question 10. [2 marks] Given the following Java function public void branch(int x) if (x < 3) if (x > 1) System.out.println("Condition1"); else if (x >=3) System.out.println("Condition2"); what will the output be when branch() is called with a) argument of 2 b) argument of 4 [2] Question 11. [4 marks] Write a Java function which does the following: reads in an integer from the keyboard (a student mark); if this mark is not in the range 50 to 100 (inclusive), prints out fail ; otherwise it prints out pass Is this sufficient to classify all marks? Why? [4] 8

9 Question 12. [4 marks] Add and using 8-bit two s complement arithmetic. Show all your working. [4] Question 13. [2 marks] Convert to Hexadecimal. Show the steps required to achieve this. Question 14. [5 marks] What is the IEEE754 single precision representation of all the steps required. [2]? Make sure to show [5] 9

10 Section 3. Java Class Files and A.I. Question 15. [6 marks] a) What is a neural network and what is it used for in Artificial Intelligence? b) What is the critical difference between a do-while loop and a while loop? c) Why is it not a good idea to use == and!= when doing floating point comparisons? d) What advantages do databases have over plain text files? [6] 10

11 Question 16. [4 marks] You are provided with the following program which is intended to help children learn mental addition: int response, guessnum = 1, op1 = 8, op2 = 7; System.out.println("What is " + op1 + " plus " + op2 + "?"); response = Keyboard.readInt("Enter guess number " + guessnum + ": "); while(response!= op1 + op2) response = Keyboard.readInt("Enter guess number " + guessnum + ": "); guesnumm++; System.out.println("Correct!"); Modify this code to use a do-while rather than a while loop and stop on the first correct guess or after five incorrect guesses (in which case the program should display Incorrect and also provide the correct answer (op1 + op2)). Question 17. [5 marks] The code below is intended to find the floating point average of a list of integer numbers terminated by the user entering a 0 value, but it contains some errors: int avg, num, count; while(num!= 0) num = Keyboard.readInt("Enter next number: "); count++; avg = avg + num; avg = avg/count; System.out.println("The average is: " + avg); [4] 11

12 a) What would this program do if executed? b) What kinds of error(s) occur during execution? Explain your answer. c) Fix the code so that it will execute correctly. d) This is an example of a sentinal loop. What does this mean? [5] 12

13 Question 18. [5 marks] You are required to write a simple program that reads text from a file. If it encounters the string DEL immediately before the end of the file then it should delete that file from the disk. You are provided with the following code skeleton, write the missing code: import java.io.*; import Keyboard; class DelFile public static void main(string[] args) throws java.io.ioexception String filename; filename = Keyboard.readString("Enter the file name for potential deletion: "); File infile = new File(filename); if (infile.exists() && infile.canread()) BufferedReader filestr = new BufferedReader(new FileReader(inFile)); // YOUR CODE FITS HERE else system.out.println("error: could not open input file"); [5] 13

14 Question 19. [5 marks] a) Why would you want to write a tostring() method for a class? b) What is the difference between a Class and an Object? c) Given the following signature for a method in the Galaxy class private double SuperNova(int centrex, int centrey, int radius) What is wrong with the following use of the Galaxy class? Galaxy milkyway = new Galaxy(); milkyway.supernova(1000.0, ); [5] 14

15 Question 20. Section 4. Arrays and Software Engineering [5 marks] Give the code below write the function enlarge that enlarges the array given to the new specified size. In this example, the array small is enlarged to 25 elements (You may NOT use the System.arraycopy() method to do this). public class exam public static void main(string[] args) int[] small = 4,2,5,3,1; enlarge(small, 25); [5] 15

16 Question 21. [7 marks] You are given the class temp below. Write a method called printlargest that can be called from outside that calculates and prints out: the highest temperature; and the position in the array where this highest value is. (In this example the answer would be 22.3 at position 2). public class temp private float[] t; public temp() // printlargest t = 14.0, 17.2, 22.3, 15.0, 13.7, 16.1, 12.2, 13.6; [7] 16

17 Question 22. [3 marks] Below you are given the class Vehicle. Using the concept of inheritance define a class called Car that extends this Vehicle class by adding two new variables, numberof- Passengers and bootcapacity (both are integers). Write the constructor for this new class. public class Vehicle private String name; private int engcapacity; public Vehicle( String n, int ec) name = n; engcapacity = ec; [3] 17

18 Question 23. [6 marks] You are given the definition below. Set the two diagonals to the value 1. Loops must be sensibly used in the solution i.e. you need to produce [6] Question 24. [6 marks] Give the steps in the Waterfall model of the traditional software life cycle model. Object oriented software development is different. Outline this approach. [3] [3] 18