Here in this program, we will code to find out the sum of non-diagonal elements and separate them with elements above the diagonal and elements below the diagonal. Here in this article, we will consider only one diagonal the left to right one.

Sum of elements above and below the main diagonal of a Matrix

For example, if the user enters the matrix-like

3  4  5

6  7  9

5  4  6

So the sum of the above diagonal elements will be 4+5+9 =18, and the sum of the below diagonal elements will be 6+5+4 = 15

C++

#include<iostream.h>
#include< conio.h>
#include<stdio.h>
#include<math.h>
void main()
{
clrscr();
int arr[4][4],ad=0, bd=0;
cout<<"Enter the elements in the array:"<<endl;
for(int i=0; i<3;i++)
{
  for(int j=0; j<3;j++)
    {cin>>arr[i][j];
     if(j>i)
       ad+=arr[i][j];
     else
       if(i>j)
         bd+=arr[i][j];
}
}
cout<<"The sum of above diagonal elements is: "<<ad<<endl;
cout<<"The sum of below diagonal elements is: "<<bd;
getch();
}

Output:

Enter the elements in the array:

3
4
5
6
7
9
5
4
6

The sum of above diagonal elements is: 18
The sum of below diagonal elements is: 15

Python

arr=[[0,0,0],[0,0,0],[0,0,0]]
ad=0
bd=0
print("Enter the elements in the array:")
for i in range(3):
    for j in range(3):
        arr[i][j] = int(input())
        if j>i:
            ad+=arr[i][j]
        else:
            if i>j:
                bd+=arr[i][j]
print("The sum of above diagonal elements is:",ad)
print("The sum of below diagonal elements is:",bd)

Output:

Enter the elements in the array:

3
4
5
6
7
9
5
4
6
The sum of above diagonal elements is: 18
The sum of below diagonal elements is: 15

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