数据一定要先预处理啊不预处理只有16分

for (int i = 1; i <= b; i++)
{
	for (int j = 1; j <= b; j++)
	{
		cin >> arr[i][j];
		if (!arr[i][j])arr[i][j] = a;
	}
}

尤其是if (!arr[i][j])arr[i][j] = a; 一定要加上