Do not turn over until you are told to do so by the Invigilator.

Transcription

1 UNIVERSITY OF EAST ANGLIA School of Mathematics UG End of Year Examination PROGRAMMING FOR MATHEMATICIANS Time allowed: TWO hours Answer ALL FOUR questions in Section A Answer ONE Question from THREE in Section B Do not turn over until you are told to do so by the Invigilator. Copyright of the University of East Anglia

2 -2- SECTION A 1.(a) Given the following declarations int a=0,b=1,c=2,d=0; give the output of the following code fragment. if(a>=d-b) System.out.println("FIRST"); if(c-2<d) System.out.println("SECOND"); else System.out.println("THIRD"); if((3*b)/c>1) System.out.println("FOURTH"); else System.out.println("FIFTH"); if(b+c*(d+a)==c-1) System.out.println("SIXTH"); else System.out.println("SEVENTH"); (b) Explain the purpose of a break statement and a default statement in a switch statement. (c) The interest rate yielded by a type of government bond depends on the length to maturity of that bond. Bonds can have a length to maturity of 10 years, 20 years or 40 years only. Assuming an integer variable length and a double variable rate have been defined, write a code fragment using a switch statement to set the rate according to the following rules rate set to 3.75 if length is 10 years rate set to 4.25 if length is 20 years rate set to 4.75 if length is 40 years your statement should print an appropriate error message if length is not a valid value. (d) Given the scenario in part (c), write a code fragment to calculate the rate that does not require selection. What are the problems of this approach [10 marks] 2

3 -3-2. The following method is meant to multiply 2 matrices of integers together, returning the result as a new matrix. It contains several errors. Identify and correct the errors. //PRE: Assumes matrices are square and the same size //POST: New matrix,multiple of m1 and m2 returned public static int matrixmultiply(int [][] m1, int [][] m2) int n=m1.length; int sum; int[][] m3 = new int[n][n]; [10 marks] for(int i==0;i<n;i++) for(int j=0;j<n;j++) for(int k=0;k<n;i++) sum+=m1[i][j]*m2[j][i]; m3[i][j]=sum; return m3; 3 TURN OVER

4 -4-3. A bank needs a class to store details about customers' bank accounts. The following information about a particular account needs to be stored name address account number current balance overdraft limit Operations that need to be performed on an account are: A default constructor to set all fields to blank (zero for numbers, single space for strings); A method validwithdrawl that checks whether an amount passed as an argument can be withdrawn from an account; A method changebalance to alter the current balance by an amount passed as an argument; A method makewithdrawl that debits an account an amount passed as an argument by calling the methods validwithdrawl and changebalance; A method isaddress that takes a string argument and returns true if the string is the same as the address recorded for this account. [12 marks] 4. A Company requires a program to store the salaries of its 20 employees. Write a code fragment that: i) reads in the 20 salary figures from the keyboard, storing the data in an array (you may assume that the expression; Keyboard.readDouble()returns a double input from the keyboard ii) finds the average salary of the employees; iii) counts and stores how many employees are in the following wage brackets 0-10,000 10,000-20,000 20,000+ [8 marks] END OF SECTION A 4

5 -5- SECTION B 5. (a) Describe the main features of a stack data structure. What operations do the two methods push and pop, commonly associated with stacks, perform on a stack? [3 marks] (b) Given the following interface public interface Stack public void push(object newobject); public Object pop(); public Object peek(); public boolean isempty(); public int size(); Define a ArrayStack class which implements this interface for Objects. Use an array with a constant size of 20 and include a constructor. [14 marks] (c) Describe an alternative data structure that could be used to store the data. Discuss the benefits of the alternative against using an array [3 marks] 5 TURN OVER

6 -6-6. (a) Describe the four main steps normally involved in the Software Development Method, giving details of the tasks required for each step. Make sure you include details how classes and methods fit in to the methodology, a description of what is meant by an algorithm and the efficiency of an algorithm and an outline of possible testing strategies. Use a simple problem such as a program to record and manipulate information about bank accounts as an example to help illustrate how to develop an application. [12 marks] (b) Explain briefly what is meant by the following terms used in the Java programming language i) references ii) abstract methods iii) polymorphism Use simple code fragments to illustrate your examples where necessary. [8 marks] 7. (a) Write a Java class called Sorts which provides a method for sorting an array of integers using the Bubble Sort algorithm. Your class should include (i) A method called swap that swaps two elements of the array of integers. (ii) A method called bubblesort which sorts the elements of the array into increasing order. [13 marks] (b) Write a method to bubble sort an array of comparable objects, overloading your bubblesort method for integer arrays. [7 marks] END OF SECTION B END OF PAPER 6