Exercise08_02.java

package ch_08;

import java.util.Scanner;

/**
 * 8.2 (Sum the major diagonal in a matrix) Write a method that
 * sums all the numbers in the major diagonal in an n � n matrix
 * of double values using the following header:
 * Write a test program that reads a 4-by-4 matrix and
 * displays the sum of all its elements on the major diagonal.
 */
public class Exercise08_02 {
    public static double sumMajorDiagonal(double[][] m) {

        double sum = 0;
        int row = 0;

        for (int column = 0; column < m.length; column++) {

            sum += m[row++][column];
        }
        return sum;

    }

    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        double[][] fourByfour = new double[4][4];

        System.out.println("Enter a 4 by 4 matrix row by row: ");

        for (int row = 0; row < fourByfour.length; row++) {
            for (int column = 0; column < fourByfour[row].length; column++) {

                fourByfour[row][column] = input.nextDouble();
            }
        }
        input.close();
        System.out.println("The sum of the elements in the major diagonal is"
                + ": " + sumMajorDiagonal(fourByfour));
    }

}