4.创建一个名为RationalNumber的类，使其具有以下功能：

1)创建一个构造函数，它可以避免分母为0，对不是约化性的分数进行约化，并且可以避免分母为负数。

2)重载类的加减乘除运算符

3)重载类的关系运算符和赋值运算符-4 Create a class named RationalNumber, and it has the following features:

1) create a constructor, it avoids the denominator is zero, for the scores is not about resistance reduction, and to avoid the denominator is negative.

2) heavy-duty class arithmetic operators

3) heavy-duty class relational operators and assignment operator