update history v1.0.0: All operation symbols can be used. Added special digital output area. Added Error message v1.1.0: Can be calculated an unlimited number of times e.g. Press the button as follows 1 + 1 = 2 + 1 = 3 v1.2.0: Added light mode v2.0.0: Decimal point added v2.1.0: Fixed the problem that multiple zeros can be entered when entering the number for the second time, and fixed the problem that the decimal point could not be used after pressing the clear key in the first step v2.1.1: bug fixed in light mode (Google Translate)
