利用栈求表达式的值，可供小学生作业，并能给出分数。(要求：建立试题库文件，随机产生n个题目；题目涉及加减乘除，带括弧的混合运算；随时可以退出；保留历史分数，能回顾历史，给出与历史分数比较后的评价。）-Use of the stack to evaluate the expression, for primary operations, and can give the scores. (Requirements: Create test database files, randomly generating n topics　topics involving addition, subtraction, mixed with the parentheses operator　ready to quit　retain historical scores, can look back at history, given scores compared with the historical evaluation.)