各位找找错，有点难，各种错误.

题主想得太复杂了，修改如下，供参考：

#include <stdio.h>
#define N 10
int main()
{
    int a[N][N], n, i, j, T, flg;
    scanf("%d", &T);
    while (T--)
    {
        scanf("%d", &n);
        if (n > 10) continue;
        for (i = 0, flg = 1; i < n; i++) {
            for (j = 0; j < n; j++){
                scanf("%d", &a[i][j]);
                if (a[i][j] != 0 && i > j)
                    flg = 0;
            }
        }
        if (flg)
            printf("YES\n");
        else
            printf("NO\n");
    }
}

//3
//3
//1 2 3
//0 4 5
//0 0 6
//YES
//2
//1 0
//- 8 2
//NO
//3
//1 2 3
//1 4 5
//0 - 1 6
//NO