实现计算器的基本功能。使之能实现基本的加、减、乘、除、开方、倒数等基本运算，同时具有存储数据的功能，能存储相关数据便于下步运算。-To achieve the basic functions of the calculator. So that it can achieve the basic addition, subtraction, multiplication, division, square root, reciprocal and other basic operations, b