CODEDOST

JAVA program to find the sum of diagonal elements of a square matrix

This JAVA program is to find the sum of diagonal elements of a square matrix.

For example, for a 2 x 2 matrix, the sum of diagonal elements of the matrix {1,2,3,4} will be equal to 5.

1     2

3    4

 Sum = 1+4 = 5

Logic

Here the procedure is almost same as the sum of elements of a matrix, only one condition needs to be added which is, we add only those elements of the matrix for which row number and column number is same, like 1^st row and 1^st column, 2^nd row and 2^nd column and so on(i==j).

Dry Run of the Program

Take input mat[][] and store elements in mat{1,2}{3,4}

Take input ‘row’ and no of rows(row) as 2

Take input ‘col’ and no of columns(col) as 2

Initialize sum=0

1st iteration for(i=0;i<row;i++) i.e. for(i=0;0<2;i++) Outer loop

1st iteration for(j=0;j<col;j++) i.e. for(j=0;0<2;j++) Inner loop

if(i==j) i.e. if(0==0)   true

sum=sum+mat[i][j];  i.e.  sum=0+mat[0][0] i.e. sum=0+1  i.e. sum=1

2nd iteration for(j=1;j<col;j++) i.e. for(j=1;1<2;j++) Inner loop

if(i==j) i.e. if(0==1)   false

2nd iteration for(i=1;i<row;i++) i.e. for(i=1;1<2;i++) Outer loop

1st iteration for(j=0;j<col;j++) i.e. for(j=0;0<2;j++) Inner loop

if(i==j) i.e. if(1==0)   false

2nd iteration for(j=1;j<col;j++) i.e. for(j=1;1<2;j++) Inner loop

if(i==j) i.e. if(1==1)   true

sum=sum+mat[i][j];  i.e.  sum=1+mat[1][1] i.e. sum=1+4  i.e. sum=5

Now we break out of inner loop and then outer loop.

Hence the sum of diagonal elements of a square matrix[1,2][3,4] would be sum=5

Program

import java.util.*;

class arr16
{  
	public static void main(String args[])
	{
		Scanner sc = new Scanner(System.in);
		
	        int i,j,row,col,sum=0;
		System.out.println("Enter the number of rows:");
		row = sc.nextInt();
		System.out.println("Enter the number of columns:");
		col = sc.nextInt();

		int[][] mat = new int[row][col];
 
    		System.out.println("Enter the elements of the matrix") ;
    		for(i=0;i<row;i++)
    		{ 
	    		for(j=0;j<col;j++)
	    		{ 
	        		mat[i][j] = sc.nextInt();
    			}
		}
		
    		System.out.println("The elements of the matrix") ;
    		for(i=0;i<row;i++)
    		{ 
	    		for(j=0;j<col;j++)
	    		{ 
	       	 		System.out.print(mat[i][j]+"\t");
    			}
      	 		System.out.println("");
		}

    		for(i=0;i<row;i++)
    		{ 
	    		for(j=0;j<col;j++)
	    		{ 
				if(i==j)	//this condition checks for diagonal
				{
					sum = sum + mat[i][j];
				}
    			}
		}

    		System.out.printf("SUM of DIAGONAL elements of the matrix = "+sum) ;
 	}	
}

Output