十进制四则运算计算器，用户输入一串四则运算表达式，系统将其以二叉链表形式存储，并输出先序、中序和后序遍历的结点顺序，最后利用栈计算后缀表达式的值，输出运算结果。-Decimal four arithmetic calculator, the user enters a string of four arithmetic expressions, the system to be stored in the binary tree, and outputs the first sequence, inorder and postorder traversal sequence of nodes, and finally the use of the suffix calculated value of the expression stack The output result of the operation.