What is my C code not printing # in staircase pattern, this is from hackerrank, I did not pass all test cases, but i can't point out why?

Write a program that prints a staircase of size n.

I did not pass through all the test cases and don't understand where I made mistake.

This is my code:

void staircase(int n) {
    char a[n][n];
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < n; j++) {
            if((i + j) > ((n / 2) + 1)) {
                a[i][j] = '#';
                printf("%c", a[i][j]);
            } else {
                printf(" ");
            }
        }
        printf("\n");
    }
}

Sample Input
6
Sample Output

     #
    ##
   ###
  ####
 #####
######

---

Explanation:

The staircase is right-aligned, composed of # symbols and spaces, and has a height and width of n=6.