算术表达式求值是以我们常用的输入算术式的方式输入式子，然后将式子以中缀表达式存储，用栈进行括号匹配最后算出结果，是初学者很好的学习数据结构的例子-The arithmetic expression is evaluated based on our common input arithmetic way input formula, then the expression to infix expression storage with stack the brackets match last