## Thursday, 25 August 2016

### Chapter 8 Exercise 1, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

*8.1 (Sum elements column by column) Write a method that returns the sum of all the elements in a specified column in a matrix using the following header: public static double sumColumn(double[][] m, int columnIndex) Write a test program that reads a 3-by-4 matrix and displays the sum of each column. Here is a sample run:

Enter a 3-by-4 matrix row by row:
1.5 2 3 4
5.5 6 7 8
9.5 1 3 1
Sum of the elements at column 0 is 16.5
Sum of the elements at column 1 is 9.0
Sum of the elements at column 2 is 13.0
Sum of the elements at column 3 is 13.0
import java.util.Scanner;

public class ProgramingEx8_1 {

public static void main(String[] args) {

double[][] matrix = new double[3][4];

java.util.Scanner input = new Scanner(System.in);
System.out.println("Enter a 3-by-4 matrix row by row: ");
for (int row = 0; row < matrix.length; row++) {
for (int column = 0; column < matrix[row].length; column++) {
matrix[row][column] = input.nextDouble();
}
}

for (int column = 0; column < matrix[0].length; column++) {
System.out.println("Sum of the elements at column " + column
+ " is " + sumColumn(matrix, column));
}

}

public static double sumColumn(double[][] m, int columnIndex) {

double sum = 0;
for (int row = 0; row < m.length; row++) {
sum += m[row][columnIndex];
}
return sum;
}

}