create a double dimension array of size 4 x 4 and calculate the sum of the diagonal elements.

In a square matrix diagonal elements are two type. In case of left diagonal the row number and column number are same. that is row no = col no. And in case of right diagonal row number + column number = (Total row number - 1). Therefore, we just travel the array once and add all the elements which meet the above conditions.

import java.util.*;
public class Diagonal2D
{
    public static void main(String []args)
    {
        Scanner sc=new Scanner(System.in);
        int s=0;
        int [][]arr=new int[4][4];
        for(int r=0;r<4;r++)
        {
            for(int c=0;c<4;c++)
            {
                arr[r][c]=sc.nextInt();
            }
        }
        for(int r=0;r<4;r++)
        {
            for(int c=0;c<4;c++)
            {
                if((r==c) || (r+c==3))    
                {
                    s+=arr[r][c];
                }
            }
        }
        System.out.println("Sum Is : " + s);
    }
}