通过4X4独立按键输入两个浮点数，并在LCD1602上进行显示，此单片机系统可精确计算两个浮点数的加减乘除，保留小数点后3位数字 -By 4X4 independent button to enter two floating-point numbers, the LCD1602 display, microcontroller system can accurately calculate the two floating-point addition and subtraction, multiplication and division, three digits after the decimal places