创建一个分数类Rational，用来执行分数的算术运算，并编写一个程序来测试该类。
（1）该类有两个成员变量，即分子和分母，均为整数类型
（2）定义一个构造函数，用来对类对象进行初始化。该构造函数必须对输入参数进行约减。例如，若给定的分数为2/4（即分子为2，分母为4），那么要把它约减为1/2，然后存储在相应的成员变量中，即分子为1，分母为2。
（3）定义一个add成员函数，实现两个分数的加法，其结果也应该是约减形式；
（4）定义一个sub成员函数，实现两个分数的减法，结果为约减形式(Create a fractional class Rational, used to perform arithmetic operations for fractions, and write a program to test the class.
(1) the class has two member variables, that is, molecules and denominator, all of which are integral types
(2) define a constructor to initialize the class object. The constructor must reduce the input parameters. For example, if a given fraction is 2/4 (i.e. the molecule is 2, the denominator is 4), we need to reduce it to 1/2, and then store it in the corresponding member variable, that is, the molecule is 1 and the denominator is 2.
(3) a add member function is defined to implement the addition of two fractions, and the result should also be reduced.
(4) a sub member function is defined to implement a subtraction of two fractions, and the result is reduced form.)