Exercise 4: Loops, Arrays and Files

Transcription

1 Exercise 4: Loops, Arrays and Files worth 24% of the final mark November 4, 2004 Instructions Submit your programs in a floppy disk. Deliver the disk to Michele Zito at the 12noon lecture on Tuesday November 24th. A submission not containing all required programs in electronic form will be penalised. Each program should be submitted in a separate text file (extension.java). Such file should contain an initial part (commented) with the analysis, comments on the solution strategy, data dictionary. 1 Exercise 1 DO NOT SUBMIT ANY WORD DOCUMENT! A matrix is a rectangular bi-dimensional array. Here is an example This is declared in Java as follows int [][] A = new int[3][4]; and then filled with the appropriate input statements (as described in the lectures). Matrices are very important in computer graphics applications. Several operations can be performed on matrices. Complete the following programming tasks (assume the elements of the matrices are integer numbers): 1. Write a program that, given a matrix A, defines another matrix B with the same number of rows and columns of A. The matrix B will have all the elements in its first row equal to zero. The elements in the first column position of each of the other rows will be the reciprocal (i.e. the same value but with the sign swapped) of the element in corresponding position of A. The element B[i][j] for all other values of i and j will be - A[i][0]*A[0][j]/A[0][0] 2. Two matrices can be added together!! " # $ ## $ ## &% ' ( ) To perform addition you simply add pairs of corresponding components. Extend the program developed for the previous question (but save this as a separate Java file) to return the sum of A and B. ( ( ) 3. Two matrices can also be multiplied together. The result of multiplying the matrices: )*+*,)*.-")*0/")*.1 )(-2*,)(-3-")(-+/")4-31 )(/2*,)(/3-")(/+/")4/ *3* 7-9* /9* 12* * / *0/ -+/ /+/ 19/ ;: :

2 is the matrix! " " " " " " " " # $ $ # $ # $ $! $ $ " # $ &% Notice that the number of columns in the first matrix must coincide with the number of rows in the second one. Moreover the resulting matrix will have as many rows as the first matrix and as many columns as the second one. Return a program that receives from the keyboard the elements of the two matrices and produces in output the result of their product (or an error message if the sizes of the two matrices are not right or any other error occur). ( ) Return your solutions as three separate programs. (Total mark ). 2 Exercise 2 Submit two different program files, one for each of the following sections. As the marking scheme suggests the first exercise is the most important. Concentrate on getting that right. If you manage to solve it, then the second part will be easy. The second part will take little time to code but it does not have any more conceptual difficulties than the first one. ' Return a working implementation of the League Table program described in the lecture. Hints: You need to implement the system designed during the lecture 9% ' Modify the League Table program to manage the Chart of the World Rugby League championship. The input this time is a number of lines of the form: TEAM1 score tries TEAM2 score tries Points are added to an overall league table with the following conventions: 1. Points (that get added to the score) can be gained by either scoring tries or kicks. 2. Each kick (following a penalty or resulting from a drop goal) is worth three points. Each kick following a try is worth two points. 3. Each try is worth five points. 4. The score is the total number of points a team earns in a match. 5. A win gives the team three points in the overall standing, a draw one point a defeat zero. 6. One bonus point in the overall standing is earned by any team that scores four tries in a match (no matter whether it wins or not). 7. One bonus point in the overall standing is earned by any team that wins with a difference of more than four tries. Assume sixteen teams take part in the tournament. Hints: start from the program for part one, and change the way in which points are awarded. 4% (Total mark: 4 ) 2

3 Marking guidelines. They have to solve two exercises. If all programs they have submitted compile then 10% of the mark for each exercise is for documentation (so 1.1% for exercise one and 1.3% for exercise two). If some (perhaps even all of them) of their programs do NOT compile then given 20% of the mark for the exercise to the documentation. To make life simple mark the documentation only once for each exercise (no matter if they have submitted separate programs for each part). We distinguish between Good and complete documentation (full mark), complete documentation (three quarters of the mark), incomplete but clear documentation (half of the mark) bad documentation (a quarter) missing documentation (no mark at all here). In the spreadsheet there is a cell for each part of each exercise. We give a mark between zero and ten to each part of each exercise (even if they have submitted a single program solving all parts, it does not matter). We try to be simple. We distinguish between Perfect, Good, Not so Good, Bad program only. After marking each exercise make sure your mark satisfies the following constraints. A program that compiles must get (at least) 25% of the mark allocated for it. If the program does NOT compile, it cannot get more than a 20% of the mark allocated for the program. Essentially there may be two reasons why the program does not compile: (a) some stupid typo (a missing or ; ) (b) major syntactic errors (these are serious). A program that produces correct results sometimes must get 50% of the mark allocated for the program. Rules on Exercise 1. The first part is about defining a matrix in terms on another one (10% of a distinction mark taken out if they don t check A[0][0]!= 0, only 5% taken out is the program is not a high quality one; Good or Perfect solutions will have a single pair of nested loops and an if statement to set B as in the program below). The second one is about the sum of two matrices. The third about the product of a matrix by a vector. See sample solution below. The following solves the first two parts (students are required to write TWO distinct programs). import java.io.*; import java.util.*; class Gauss { // global declarations static BufferedReader keyboard = new BufferedReader ( new InputStreamReader(System.in) ); public static void main (String[] args) throws IOException { double [][] A; double [][] B; double [][] C; double [] X; int n, m; StringTokenizer data; System.out.print("Please enter the dimensions of A: "); if (data.counttokens() == 2) { n = new Integer(data.nextToken()).intValue(); m = new Integer(data.nextToken()).intValue(); // the number of rows and columns is now fixed, no possibility // of a mistake. If X is defined later and you choose to input // its dimension again then you need to check that the sizes are // right. A = new double [n][m]; B = new double [n][m]; C = new double [n][m]; X = new double [m]; 3

4 // You may prefer to use the tokenizer again here... (I think // the code becomes a bit more complex). for ( int i = 0 ; i < n ; i++) { System.out.print("A["+(i+1)+","+(j+1)+"] = "); A[i][j] = new Double(keyboard.readLine()).doubleValue(); // Definition of B. for ( int i = 0 ; i < n ; i++) if (i==0) B[i][j] = 0.0; else if (A[0][0]!=0.0) B[i][j] = - A[i][0]*A[0][j]/A[0][0]; else { System.out.println("The PIVOT is zero!!! I am getting out of here!"); break; // Computing A+B if (A[0][0]!=0.0) { for ( int i = 0 ; i < n ; i++) C[i][j] = A[i][j] + B[i][j]; // printing what is going on System.out.println("Matrix A"); for ( int i = 0 ; i < n ; i++) { System.out.print(A[i][j] + " "); System.out.println(); // printing what is going on System.out.println("Matrix B"); for ( int i = 0 ; i < n ; i++) { System.out.print(B[i][j] + " "); System.out.println(); // printing what is going on System.out.println("Matrix C"); for ( int i = 0 ; i < n ; i++) { System.out.print(C[i][j] + " "); System.out.println(); else System.out.println("You did not give me the number of rows and columns of A."); The product program should be along the following example: import java.io.*; import java.util.*; class Matrix\_Prod { static BufferedReader keyboard = new BufferedReader ( new InputStreamReader(System.in) ); public static void main(string[] args) throws IOException { int dim1, dim2; int[][] A; int dim3, dim4; 4

5 int[][] B; int b1, b2, b3, b4; int partial; StringTokenizer data; int i, j; int k; // read the first matrix dimension dim1 = new Integer( data.nexttoken()).intvalue(); dim2 = new Integer( data.nexttoken()).intvalue(); A = new int[dim1][dim2]; // read the first matrix values for ( i = 0; i < dim1; i++ ) { // checks on the presence of a valid array of values // can be added here to get more distinction marks for ( j = 0; j < dim2; j++ ) // checks on the presence on next token, using // token counter can be used here. A[i][j] = new Integer( data.nexttoken()).intvalue(); // read the second matrix dimension dim3 = new Integer( data.nexttoken()).intvalue(); dim4 = new Integer( data.nexttoken()).intvalue(); if ( dim2 == dim3 ) { B = new int[dim3][dim4]; System.out.println( "Multiplying two matrices"); // read the second matrix values for ( i = 0; i < dim3; i++ ) { // checks on the presence of a valid array of values // can be added here to get more distinction marks for ( j = 0; j < dim4; j++ ) // checks on the presence on next token, using // token counter can be used here. B[i][j] = new Integer( data.nexttoken()).intvalue(); // produce the resulting matrix for ( i = 0; i < dim1; i++ ) { for ( j = 0; j < dim4; j++ ) { partial = 0; for ( k = 0; k < dim3; k++ ) partial = partial + (A[i][k]*B[k][j]); System.out.print( partial + " "); System.out.println(); else System.out.println("The dimensions of the two matrices do not match!"); As test case use the following: 5

6 # 5 # # " % " # Specific rules Exercise 2. A complete solution must contain two programs. The different programs are worth.1%, 3.6% respectively (the 10% for the documentation has been subtracted). One needs to be hard in marking the first exercise, but then easily give 10 marks for exercise 2 if it is correct. Ex. 2.1 The following is a sample solution which would get 90% of the program marks for this question (this is 1% of the full mark for this question (this is what I call mark in absolute terms below). A better solution should cope with input checks, as follows. Every time something is read from the input file a number of checks could be enforced to test whether the number of tokens in the line just read is right (4%, in absolute terms) and if the team names are consistent (5%). Overall assign max 9% (which takes the overall percentage for the program to 90%). Penalise solutions in which not all variables declared are necessary (max -10% mark in absolute terms) or they are NOT like specified in the design provided during the Lectures. Programs that only work for results of two weeks get 60% in absolute terms. // chap_5\ex_ // program to calculate the league chart based on a number of results // stored in a text file "results.txt" import java.io.*; import java.util.*; class League { // The program has no reader from input. It will get all its data from // a file. public static void main(string[] args) throws IOException { // I am using a league of 20 teams final int NUMBER_OF_TEAMS = 20; // File containing all results. FileReader file = new FileReader("results.txt"); BufferedReader inputfile = new BufferedReader(file); StringTokenizer data; // Output data structures String[] Teams = new String[NUMBER_OF_TEAMS]; int[] points = new int[number_of_teams]; // Internal representation of a week results. We need it // to be the full table if we want to split the initialisation // of the score chart (first loop) from its updating. String[][] weekresults = new String[NUMBER_OF_TEAMS/2][4]; // counters int match, i; boolean TeamListHasBeenSet = false; for ( i = 0; i < NUMBER_OF_TEAMS; i++) points[i] = 0; // read week results from the file results.txt and store this // data in a two-dimensional array. // The first readline reads in the WEEK 1 banner. 6

7 while (!data.nexttoken().equals(".")) { // Enter data for the next week for ( match = 0; match < (NUMBER_OF_TEAMS/2); match++) { // The following instruction reads one after the other // the results of a week. for ( i = 0; i < 4; i++) weekresults[match][i] = data.nexttoken(); if (!TeamListHasBeenSet) { Teams[2*match] = weekresults[match][0]; Teams[2*match + 1] = weekresults[match][2]; // Teams will not be changed any more. TeamListHasBeenSet = true; // Updates the various teams points based on the latest results. for ( match = 0; match < (NUMBER_OF_TEAMS/2); match++) { // Find the index of the team. i = 0; while (!Teams[i].equals(weekResults[match][0])) i++; if ((new Integer(weekResults[match][1]).intValue()) > (new Integer(weekResults[match][3]).intValue())) points[i] = points[i] + 3; else if ((new Integer(weekResults[match][1]).intValue()) == (new Integer(weekResults[match][3]).intValue())) i = 0; while (!Teams[i].equals(weekResults[match][2])) i++; if ((new Integer(weekResults[match][1]).intValue()) < (new Integer(weekResults[match][3]).intValue())) points[i] = points[i] + 3; else if ((new Integer(weekResults[match][1]).intValue()) == (new Integer(weekResults[match][3]).intValue())) // The next instruction reads a new line from the text file. System.out.println("League Table\n"); System.out.println("Team\tTotal\n"); for ( i = 0; i < NUMBER_OF_TEAMS; i++) { if (Teams[i].length() > 7) System.out.println(Teams[i].substring(0,7) + "\t" + points[i]); else System.out.println(Teams[i] + "\t" + points[i]); Ex. 2.2 The modification on Ex. 2.1 is obvious. Give the full marks (plus whatever comes from the documentation) for a program that differs from the one solving 2.1 only for the size of the internal data structure for the week results, for the different place where the points can be computed and for the few more instructions needed to deal with bonus points. The final output part should be exactly the same as for exercise

8 Any more complicate CORRECT solution gets a pass mark. // program to calculate the rugby league chart based on a number of results // stored in a text file "results.txt" import java.io.*; import java.util.*; class RugbyLeague { // The program has no reader from input. It will get all its data from // a file. public static void main(string[] args) throws IOException { // I am using a league of 10 teams final int NUMBER_OF_TEAMS = 10; // File containing all results. FileReader file = new FileReader("rugby.txt"); BufferedReader inputfile = new BufferedReader(file); StringTokenizer data; // Output data structures String[] Teams = new String[NUMBER_OF_TEAMS]; int[] points = new int[number_of_teams]; // Internal representation of a week results. We need it // to be the full table if we want to split the initialisation // of the score chart (first loop) from its updating. String[][] weekresults = new String[NUMBER_OF_TEAMS/2][6]; // counters int match, i; boolean TeamListHasBeenSet = false; for ( i = 0; i < NUMBER_OF_TEAMS; i++) points[i] = 0; // read week results from the file results.txt and store this // data in a two-dimensional array. // The first readline reads in the WEEK 1 banner. while (!data.nexttoken().equals(".")) { // Enter data for the next week for ( match = 0; match < (NUMBER_OF_TEAMS/2); match++) { // The following instruction reads one after the other // the results of a week. for ( i = 0; i < 6; i++) weekresults[match][i] = data.nexttoken(); if (!TeamListHasBeenSet) { Teams[2*match] = weekresults[match][0]; Teams[2*match + 1] = weekresults[match][3]; // Teams will not be changed any more. TeamListHasBeenSet = true; // Updates the various teams points based on the latest results. for ( match = 0; match < (NUMBER_OF_TEAMS/2); match++) { // Find the index of the team. i = 0; while (!Teams[i].equals(weekResults[match][0])) i++; if ((new Integer(weekResults[match][1]).intValue()) >

9 (new Integer(weekResults[match][4]).intValue())) points[i] = points[i] + 3; else if ((new Integer(weekResults[match][1]).intValue()) == (new Integer(weekResults[match][4]).intValue())) if ((new Integer(weekResults[match][2]).intValue()) >= 4) if ((new Integer(weekResults[match][2]).intValue()) > (new Integer(weekResults[match][5]).intValue())+3) i = 0; while (!Teams[i].equals(weekResults[match][3])) i++; if ((new Integer(weekResults[match][1]).intValue()) < (new Integer(weekResults[match][4]).intValue())) points[i] = points[i] + 3; else if ((new Integer(weekResults[match][1]).intValue()) == (new Integer(weekResults[match][4]).intValue())) if ((new Integer(weekResults[match][5]).intValue()) >= 4) if ((new Integer(weekResults[match][5]).intValue()) > (new Integer(weekResults[match][2]).intValue())+3) // The next instruction reads a new line from the text file. System.out.println("League Table\n"); System.out.println("Team\tTotal\n"); for ( i = 0; i < NUMBER_OF_TEAMS; i++) { if (Teams[i].length() > 7) System.out.println(Teams[i].substring(0,7) + "\t" + points[i]); else System.out.println(Teams[i] + "\t" + points[i]); 9