The concepts such as mathematical expression, stackoperation and binary tree traversal must be presented in data structure.
数学表达式、栈的操作、二又树的遍历，这几个概念在数据结构的教材中是不可缺少的。
2
The realizing recursive algorithm by stack and the Changing recursive algorithm into non-recursive by stackoperation are studied. The thinking of recursion and its application are expounded.
分析递归算法的栈实现以及用栈运算转换递归算法为非递归算法，阐述递归思想及其应用。
3
If the character is an operator, pop two operands, perform the appropriate operation, and then push the result onto the stack.