利用结构体定义结点，每个结点有前驱指针与后继指针，结点数据也是用指针动态开辟内存，每个前驱指针指向前一个结点，每个后继指针指向后一个结点实现双向循环列表，新数据插入可选择首部插入与尾部插入-Use structure is defined nodes, each node has predecessor and successor pointers pointer, node data also opened with a pointer dynamic memory, each precurs