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 read integer or real number. That needs to be read into the string of numbers that makes up the value.