c++实现currency类（两种）

c++实现一个currency类——简要说明

练习来自[美]萨特吉·萨尼（Sartaj Sahni）写的c++语言描述——数据结构、算法与应用中第一章c++回顾知识
其中区别开了两个currency类，复制粘贴可得到旧currency类，对/**/进行删除后可以使用新的currency类，并有附加函数操作
这是一个菜鸟的练习日记，所有的理解与学习都在代码中注释出来了，不知道这样的备注方式对不对，如果你有更好的意见，欢迎提出

代码

#include<iostream>
#include<string>
using namespace std;
enum signType{ 
   plus,minus};
//本打算用枚举类型进行的
//但vs2017并不能识别plus和minus，故换成bool，其中+为0，-为1

class illegal_Parameter_Value
{ 
   //异常类，输入不正确信息时用来抛出
public:
	illegal_Parameter_Value() :message("Illegal parameter value") { 
   }
	//构造函数
	illegal_Parameter_Value(const char* theMessage) { 
    message = theMessage; }
	//复制构造函数，如同调用构造函数的初始化的“”内容为const char*类型，故声明为该形式，const不可少
	void outputMessage() { 
    cout << message << endl; }
private:
	string message;
};
//报错类

class currency
{ 
   //类声明
public:
	currency(bool the_Sign = 0, unsigned long the_Dollars = 0, unsigned int the_Cents = 0);
	//构造函数，三输入，若无变量进行构造就赋值为0,0,0，该值为缺省值
	//若初始值少于参数个数（有参数输入），就按顺序初始化，剩下的按照缺省值进行初始化
	~currency() { 
   };
	//析构函数
	void setValue(bool, unsigned long, unsigned int);
	void setValue(double);

	bool getSign()const { 
    return sign; }
	unsigned int getdollar()const { 
    return dollars; }
	unsigned long getcent()const { 
    return cents; }
	//const关键字指明 上方成员函数不会改变调用对象的值，故又称常量函数
	currency add(const currency&)const;
	//此处的加法函数不会改变调用对象的值，而是作为一个currency类型的值存在于环境中，也不会改变调用该函数的参数的值，故为常量函数
	//add返回对象的值
	currency&increment(const currency&);
	//此处的加法函数会改变调用对象的值，故非常量函数，并且使用引用，可以减少函数在最后返回对象的结果时的复制的时间
	//increment返回对象的引用
	void output()const;

	//附加算法
	void input();//从标准流中读取currency的值，然后赋给调用对象
	currency subtract(const currency&x)const;//从调用对象中减去参数对象x的值，返回结果（已实现）
	//未实现下列三个函数
	currency percent(const double&x)const;//返回一个currency类的对象，它的值是调用对象的x%。x为double型
	currency multiply(const double&x)const;//返回一个currency类的对象，它的值是调用对象和x的乘积。x为double型
	currency divide(const double&x)const;//返回一个currency类的对象，它的值是调用对象除以x的结果。x为double型
private:
	bool sign;
	unsigned long dollars;
	unsigned int cents;
};
/* class new_currency {//新的类把小数点前后的值合起来用double存储了 public: new_currency(bool the_sign = 0, unsigned long the_dollars = 0, unsigned int the_cents = 0); ~new_currency() {} void set_value(bool, unsigned long, unsigned int); void set_value(double); bool getsign()const { if (amount < 0)return 1; else return 0; } unsigned long get_dollars()const { if (amount < 0)return (-amount) / 100; else return amount / 100; } unsigned int get_cents()const { if (amount < 0)return (-amount) - get_dollars(); else return amount - get_dollars(); } new_currency add(const new_currency&x)const; new_currency &increment(const new_currency&x) { amount += x.amount; return *this; } new_currency operator +(const new_currency&)const; new_currency& operator+=(const new_currency&x) { amount += x.amount; return *this; } void output(ostream&out)const;//调用全局范围的函数ostream&operator<<(ostream&out,const new_currency&)即可使用<< friend ostream&operator<<(ostream&output,const new_currency&x); private: double amount; }; //一个新的currency类，把dollar和cent用amount一个数存储，并且amount为整数 */

currency::currency(bool the_Sign, unsigned long the_Dollars, unsigned int the_Cents)
{ 
   
	setValue(the_Sign, the_Dollars, the_Cents);
}
//调用成员函数初始化
void currency::setValue(bool the_Sign, unsigned long the_Dollars, unsigned int the_Cents)
{ 
   //给调用对象的数据成员赋值
	if (the_Cents > 99)throw illegal_Parameter_Value("cents should be<100");//当输入过大时抛出非法信息
	sign = the_Sign;
	dollars = the_Dollars;
	cents = the_Cents;
}
void currency::setValue(double the_Amount)
//double和float可带符号
{ 
   
	if (the_Amount < 0)//判断输入数的正负，并提取前边符号
	{ 
   
		sign = 1;
		the_Amount = -the_Amount;
	}
	else sign = 0;
	dollars = (unsigned long)the_Amount;//强制转换为无符号，去除符号问题，其中unsigned long加不加int都一样
	cents = (unsigned int)((the_Amount + 0.001 - dollars) * 100);//0.01弥补计算机存储数据总会偏小的误差，强制转换数据类型
}//long占四字节，int在16位系统中占2字节，在32位系统中占4字节，故一般情况是一样的，包括unsigned int和unsigned long
currency currency::add(const currency& x)const
{ 
   
	double a1, a2, a3;
	currency result;//返回一个新声明的变量就不会改变输入参量的值了
	a1 = dollars * 100 + cents;
	if (sign == 1)a1 = -a1;//此时a1为带符号的double型
	a2 = x.dollars * 100 + x.cents;
	if (x.sign == 1) a2 = -a2;
	a3 = a1 + a2;//a3符号由运算得来
	if (a3 < 0)//分离a3的符号和数值
	{ 
   
		result.sign = 1;//给result变量符号赋值
		a3 = -a3;//a3为数值，不带符号
	}
	else result.sign = 0;
	result.dollars = a3 / 100;
	result.cents = a3 - result.dollars * 100;
	return result;//返回result不改变调用的参数值
}
currency& currency::increment(const currency& x)
{ 
   //把参数对象的货币值加到调用对象上，这个函数改变了调用对象的值,不改变引用的x的值，并且x前有const声明
	*this = add(x);
	return *this;//返回到x中，改变参数值
}
void currency::output()const
{ 
   
	if (sign == 1)cout << "-";
	cout << "$" << dollars << ".";
	if (cents < 10)cout << "0";
	cout << cents << endl;
}
currency currency::subtract(const currency&x)const
{ 
   //课后题
	currency result;
	double y1, y2;
	if (sign == 1)
	{ 
   
		y1 = -(dollars * 100 + cents);
		//cout << "y1一开始为负，此时应当为正：" << y1 << endl;
	}
	y1 = dollars * 100 + cents;
	//cout << "对y1操作之后y1应为一正数：" << y1 << endl;
	if (x.sign == 1)
		y2 = -(dollars * 100 + cents);
	y2 = x.dollars * 100 + x.cents;
	//cout << "对y2操作之后y2应为一正数：" << y2 << endl;
	double y3 = y1 - y2;
	//cout << "y1-y2=" << y3 << endl;
	if (y3 < 0)
	{ 
   
		y3 = -y3;
		result.sign = 1;
	}
	else
		result.sign = 0;
	result.dollars = y3 / 100;
	//cout << "result.dollars=";
	//cout << result.dollars << endl;
	result.cents = y3 - result.dollars * 100;
	//cout << "result.cents=" << result.cents << endl;
	return result;
}
/* new_currency::new_currency(bool the_sign, unsigned long the_dollars, unsigned int the_cents) { set_value(the_sign, the_dollars, the_cents); } void new_currency::set_value(bool the_sign, unsigned long the_dollars, unsigned int the_cents) { if (the_cents > 99) throw illegal_Parameter_Value("too much cents,the cents should below 100"); if (the_sign == 1) { double the_numbers = the_dollars * 100 + the_cents; amount = -the_numbers; } else amount = the_dollars * 100 + the_cents; } void new_currency::set_value(double Amount) { if (Amount < 0) amount = (Amount - 0.001) * 100; else amount = (Amount + 0.001) * 100; } new_currency new_currency::add(const new_currency&x)const { new_currency y; y.amount = x.amount + amount; return y; } //******************************************************************************************** //******************************************************************************************** void new_currency::output(ostream &out)const {//若没有下方输出流的定义，此处的输出流会出error double Amount; //将平时使用的cout换为输入参数即可 if (amount < 0) { out << "-"; Amount = -amount; } else Amount = amount; unsigned long dollars = Amount / 100; out << "$" << dollars << "."; unsigned int cents = Amount - dollars * 100; if (cents < 10) out << "00"; out << cents; } ostream&operator<<(ostream&out, const new_currency&x) {//格式即ostream&operator<<(ostream&,自定义类&) //谭浩强c++教程中p314谈及输入输出流不能定义为成员函数，只能定义为友元函数，此处即非成员函数 x.output(out); //需要先定义一个类的输出函数，并使输出函数有参数，并且还要是ostream的引用作为参数输入 return out; //返回一个对象的引用后续可以对同一个对象进行其他操作，返回对象只是返回一个拷贝副本，无法进行后续操作 //如cout<<a<<b<<endl; //此处cout的<<函数返回的就是引用，连续使用输出流即引用符号的效果 } //此处为全局范围的函数 //******************************************************************************************** //******************************************************************************************** new_currency new_currency::operator+(const new_currency&x)const { new_currency y; y.amount = amount + x.amount; return y; } ostream&operator<<(ostream&output,const new_currency&x) { double the_amount; if (x.amount < 0) { output << "-"; the_amount = -x.amount; } else the_amount = x.amount; unsigned long dollar = the_amount / 100; unsigned int cent = the_amount - dollar * 100; output << "$" << dollar << "."; if (cent < 10) output << "0"; output << cent; return output; } */
int main()
{ 
   
	currency g, h(0, 3, 50), i, j;
	g.setValue(1, 2, 25);
	cout << "g的值为：" << endl;
	g.output();
	cout << "g.add(h)的值为：" << endl;
	g.add(h).output();
	cout << "g.abstract(h)的值为：" << endl;
	g.subtract(h).output();
	cout << "h的值为：" << endl;
	h.output();
	cout << "g.increment(h)的值为：" << endl;
	g.increment(h).output();
	cout << "h的值为：" << endl;
	h.output();
	cout << "g的值为：" << endl;
	g.output();
	cout << "h的值为：" << endl;
	h.output();
	i.setValue(-6.45);
	j = h.add(g);
	h.output();
	cout << "+";
	g.output();
	cout << "=";
	j.output();
	cout << endl;
	j = i.add(g).add(h);
	j = i.increment(g).add(h);
	cout << "Attempting to initialize with cents = 152" << endl;
	try { 
    i.setValue(0, 3, 152); }
	catch (illegal_Parameter_Value e)
	{ 
   
		cout << "Caught thrown exception" << endl;
		e.outputMessage();
	}
	/* new_currency a, b(0, 3, 50), c, d; a.set_value(1, 2, 25); c.set_value(-6.25); cout << "a= " << a << endl; cout << "b= " << b << endl; cout << "c= " << c << endl; cout << "d= " << d << endl; d = b + a; cout <<" d=b+a: "<< b << "+" << a << "=" << d << endl<<endl; d = a + b + c; cout <<"d=a+b+c： "<< a << "+" << b << "+" << c << "=" << d << endl; cout << "increment of new_currency: " << c << "by: " << a << endl << "and then add:" << b << endl; d = (c += a) + b; cout << "the result is : " << d << endl; cout << "incremented object is: " << c << endl; //error testing cout << "attempting to initialize with cents=152" << endl; try { c.set_value(0, 3, 152); } catch (illegal_Parameter_Value e) { cout << "caught thrown exception" << endl; e.outputMessage(); }*/
	return 0;
}