QT编写功能及界面，实现功能：加、减、乘、除、连加、连减、连乘、连除、加减乘除混合运算、除零报错等功能，代码简单清晰，适用于刚刚接触QT的人-QT write functions and interface functionality: add, subtract, multiply, divide, even increase, even less, and even multiply, even in addition, subtraction, multiplication and div