C-program to Find the Diagonal sum of a square matrix

#include<stdio.h>
main()
{
int a[50][50],o,i,j,d1=0,d2=0;
  printf("Enter the order of square matrix\t");
  scanf("%d",&o);
  printf("Enter %d elements of the matrix:\n",(o*o));
  for(i=0;i<o;i++)
    for(j=0;j<o;j++)
          scanf("%d",&a[i][j]);
  printf("matrix representation of above elemnts is\n");
for(i=0;i<o;i++)
{
for(j=0;j<o;j++)
printf("%d\t",a[i][j]);
printf("\n");
}
for(i=0,j=o-1;i<o||j>=0;i++,j--)
    {
    d1=d1+a[i][i];
    d2=d2+a[i][j];
    }
    printf("\nFirst diagonal's SUM\t%d",d1);
    printf("\nSecond diagonal's SUM\t%d",d2);
}  

output