说明：  利用伟福 Lab2000P单片机实验仪上提供的显示电路和键盘电路，做一个简单的计算器。用十六进制A键 =‘+’、B键 =‘-’、C键 = ‘x’、D键 = ‘/’、E键 = ‘=’、F键 = ‘C’。
(Wei Fu Lab2000P use of single-chip experiment to provide the display circuit and the keyboard circuit, make a simple calculator. A hexadecimal key =)