For diagonal difference this logic is showing a garbage value. Where am I doing wrong?

Question

int main()
{
    int i,a[3][3];
    int diagonal_diff;

    int lsum=0,rsum=0;
    for(i=0;i<3;i++){
       lsum=lsum+a[i][i];
       rsum=rsum+a[i][2-i];
      }
     diagonal_diff= abs(lsum-rsum);
     printf("%d",diagonal_diff);

}