编写完成模拟小型计算器功能的程序。只能从键盘读字符，包括数字符和运算符等，而不能直接读整数或实数。即，需要将读入的数字串拼成数值。-Prepared and analog functions of a small calculator program. Can only be read from the keyboard characters, including the number of characters and operators, etc., but can not directly