定义一个顺序队列，可以对队列进行“入队”、“出队”、“清空队列”、“获取队首元素”等操作。键盘输入一些命令，可以执行上述操作。本题中，队列的元素为字母， 队列的最大元素个数为1-Define a sequential queue, you can queue " into the team," " the team" , " Clear Queue" , " get the first element of the team"