[C++知识库]c++ 自定义类 class

#include<iostream>
using namespace std;
enum signType{plus,minus};
class currency{
   
     public:
       currency (signType theSign= signType::plus,unsigned long theDollars=0,unsigned int theCents = 0); //构造函数  外部定义  诺省初始值--> 则按此默认给
        ~currency(){};//析构函数 为空 
        void setValue(signType,unsigned long,unsigned int ); //原型 定义在class 外部 
        currency add(const currency&) const; //此const表示 不改变参数的内容 
        void output() const;

        private :  //只能通过成员函数访问  不能对象私自 访问
            signType sign;
            unsigned long dollars;
            unsigned int cents;
}; //最后也要加分号

 currency::currency (signType theSign,unsigned long theDollars,unsigned int theCents){
     setValue(theSign,theDollars,theCents);
}
void currency::setValue(signType Sign,unsigned long Dollars,unsigned Cents){ // 如显示初始化对象 ，则调用此  64row
    //给调用对象 的成员赋值 
     if(Cents >99){
          throw "Max of Cents";
     }
      sign = Sign;   //没用 . 就代表 访问 调用对象的成员 
      dollars = Dollars;
      cents = Cents;
}
currency currency::add(const currency & x) const{
    currency result;
    long a1,a2,a3;
    a1=dollars*100 + cents;  //a1 调用对象的 转换为数字值 
    if(sign ==signType:: minus)
       a1 = -a1;

       a2 = x.dollars*100 +x.cents; // a2 代表形参传进来的对象 
        if(x.sign == signType:: minus)
          a2= -a2;
      
       a3= a1+a2;
        if(a3<0){
             result.sign =signType:: minus;
              a3 = -a3;
        }
           else  result.sign = signType::plus;

        result.dollars = a3/100;
        result.cents = a3-result.dollars*100;

        return result;
          
}
 void currency::output() const{
      if(sign == signType::minus)
        cout<<'-';
          cout<< dollars
               << '.'
                << cents;
 }

int main(){
    currency a(signType::plus,3,22),b(signType ::minus,2,22);
    a =a.add(b);
    a.output();

    return 0;
}