查找线性表中的某元素：L为带头接点的单链表的头指针，当第i个元素存在的时候，其值赋给e并返回OK,否则返回ERROR */ -linear search of a table of elements : L tap for the lead single linked list for the first guide, When the first i elements exist, the value assigned to the e and return to the lounges, or else return ERROR* /