编写一个商品类Goods，里面有单价price和数量number两个私有数据成员，并用构造方法实现数据成员初始化，用cost（）计算花费的总价；2）在主函数中通过调用cost（）计算马云云所花费的钱。(1) write a commodity class goods, which has two private data members: unit price and quantity number, and use the construction method to initialize the data members, and use cost () to calculate the total cost; 2) in the main function, call cost () to calculate the cost of Ma yunyun.)