introduction of Stack

Insertion and deletion of data only occurs at one end either from front or from back of the list.<br>The data cannot be retrieved randomly from any position. But data can be retrieved only from one end.数据的插入与删除操作仅可在列表（list）的单一端点执行，该端点可为列表的头部或尾部。 无法从任意位置随机访问数据，仅可通过该单一端点获取数据。