说明：  本程序的功能，就是实现数的加减乘除四则运算，并对运算符的优先级进行运算。输入的表达式中最多有3个运算符，数据范围为1-100的整数；如：输入13-10+5/8时输出3.625。
(The program functions, is to realize the number of addition and subtraction, multiplication and division arithmetic, and operator precedence for operation. Enter an expression in a maximum of three operators, the data range 1-100 integer such as: Input 13-10+5/8 output 3.625.)