C program to add diagonal elements of matrix?

#include<stdio.h>
 
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 );
     
getch();

}