Sum the diagonal elements in a matrix

/* C Program to find Sum of Diagonal Elements of a Matrix */

#include<stdio.h>
 
int main()
{
  int i, j, rows, columns, a[10][10], Sum = 0;
  
  printf("\n Please Enter Number of rows and columns  :  ");
  scanf("%d %d", &i, &j);
 
  printf("\n Please Enter the Matrix Elements \n");
  for(rows = 0; rows < i; rows++)
   {
     for(columns = 0;columns < j;columns++)
     {
        scanf("%d", &a[rows][columns]);
     }
   }
      
  for(rows = 0; rows < i; rows++)
   {
     Sum = Sum + a[rows][rows];
   }
 
  printf("\n The Sum of Diagonal Elements of a Matrix =  %d", Sum );

  return 0;
}

https://www.tutorialgateway.org/c-program-to-find-sum-of-diagonal-elements-of-a-matrix/