实现从键盘终端输入语法正确的算术表达式，计算出表达式的值。为了避免算符的二义性，可以假设表达式中只包含实型正常数运算符包括加、减、乘、除四种基本运算，可以包含圆括号。-Realized syntactically correct input from the keyboard terminal arithmetic expressions to calculate the value of the expression. To avoid ambiguity operator, it can b