说明：  表达式求值主要使用的数据结构是栈，因为栈具有后进先出的特点，与表达式求值时的符号和数值运算过程是刚好相符合的。表达式求值也是栈的一个典型的运用。
(Expression evaluation is the main data structure used in the stack, because the stack has the characteristics of LIFO, and expression evaluation when the process of symbolic and numerical computing is exactly consistent. Expression evaluation is also a typical use of the stack.)