能够处理以字符序列的形式输入的不含变量的实数表达式，正确处理负数与小数，判断表达式是否语法正确（包含分母不能为零的情况），正确实现对算术四则混合运算表达式的求值，能够将计算中遇到的问题和结果以文件的形式予以存储；-In character series to be able to deal with the form of the input variables of the real number does not contain expression, dealing with the negative and decimal, judge whether expression grammar correctly (including the denominator can t to zero), the right to realize four mixed operation expression of the arithmetic for value, can will calculate the problem in and results to file form to storage