设计一个简易的计算器，实现加、减、乘、除、开方等运算。
要求：前面板设有数字控制器用来输入数字，数字显示器用来显示运算结果。
前面板设有数字控制器用来输入两个数字，数字显示器用来显示运算结果。运算方式有加、减、乘、除。
要求：用一个滚动条来规定运算方式。(Design a simple calculator to add, subtract, multiply, divide, square and other operations.
Requirements: The front panel is equipped with a digital controller for inputting numbers and a digital display for displaying operation results.
The front panel is equipped with a digital controller to input two numbers, and the digital display is used to display the result of operation. There are addition, subtraction, multiplication and division.
Requirements: use a scroll bar to specify the operation mode.)