Count null diagonals in a matrix -

i'm trying create program counts number of null diagonals in square matrix, can't seem find correct way of making index run correctly through matrix. here's incorrect code i've got far:

# include<stdio.h>  # define max 100  int diagonnull (int n, int a[max][max]) { int i, j, count, null;  banda = 0;  for(i = n - 1; >= 0; i--){     count = 0;     for(j = 0; j <= n && j < - 1; j++){         if (a[i][j] == 0)             count++;     }     if (count == n - i) /* n - = number of elements in diagonal */         null++;     else         = - 1; } return null; }  int main () {  int n, a[max][max], i, j, null; printf ("enter value of n create square matrix of order n: "); scanf ("%d", &n);  printf ("enter elements of matrix a: "); (i = 0; < n; i++){     (j = 0; j < n; j++){         scanf("%d", &a[i][j]);     } }  null = diagonnull (n, a); printf ("matrix has null %d diagonals", null);  return 0; }