C++ 继承：Package继承层次

创建 Package类

【问题描述】

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• 一些快递商，如 FedEx、DHL和UPS，都提供多样化的服务，同时也收取不同的费用。创建一个表示各种不同包裹的继承层次。以包裹类Package作为基类，两日包裹类TwoDayPackage和连夜包裹类OvernightPackage作为派生类。
• 基类Package应该包括含代表寄件人和收件人姓名、地址、所在城市、所在州和邮政编码等的数据成员。此外，还应包含存储包裹重量(以盎司计)和每盎司费用的数据成员。类的构造函数应初始化这些数据成员，并确保重量和每盎司费用为正值。Package应该提供public成员函数calculateCost，该函数计算重量和每盎司费用的乘积，得到的是与运输该包裹有关的费用并返回(返回值类型为double)。
• 派生类TwDayPackage应继承基类Package的功能，但还应包含一个数据成员，表示给两日快递服务的平寄费。TwoDayPackage构造函数应接受一个值来初始化这个数据成员。类TwoDayPackage还应该重新定义基类的成员函数calculateCost计输费用，具体方法将平寄费加到基类Package的 calculateCost函数计算得到的基于重量的费用中。
• 派生类OvenightPackage应直接继承基类，并且应包含一个附加的数据成员，表示付给连夜快递服务的每盎司的额外费用。类 OvernightPackage应当重新定义基类的成员函数calculateCost来使它在计算运输费用之前,先将额外每盎司费用加到标准的每盎司费用上。
• 编写测试程序，创建每种Package的对象并测试成员函数 calculateCost。

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【相关的解决方法】

1.编写基类Package

class Package
{
	public://声明为常量引用，使用引用避免copy，使用const能保护数据 
		Package(const string&,	const string&, const string&, const string&,const string&, int , double , double);
		double calculateCost() const;
		double getWeight() const;
		double getCostPerOunce() const;
	private:
		string senderName;		
		string recipientName;
		string address;
		string city;
		string state;
		int postalCode;
		double weight;
		double costPerOunce;//Cost per ounce每一盎司费用 ；盎司：英美制单位，既是重量单位又是容量单位 
};

2.两日包裹类TwoDayPackage，继承于Package类

class TwoDayPackage : public Package
{
	public:
		TwoDayPackage(const string&, const string&, const string&, const string&,const string&, int , double , double, double);
		double calculateCost() const;//基类的成员函数需要在派生类内声明才可被使用 
	private:
		double surfaceMailCosts;//平寄费 
};

3.连夜包裹类OvernightPackage，继承于Package类

class OvernightPackage : public Package
{
	public:
		OvernightPackage(const string&, const string&, const string&, const string&,const string&, int , double , double, double);
		double calculateCost() const;
	private:
		double extraCosts;//连夜快递服务的额外费用 
};

4.Package类的构造函数初始化数据成员，并确保重量和每盎司费用为正值，提供public成员函数calculateCost，该函数计算重量和每盎司费用的乘积，得到的是与运输该包裹有关的费用并返回(返回值类型为double)。

Package::Package(const string& senderName1,const string& recipientName1, const string& address1, const string& city1,const string& state1,int postalCode1, double weight1, double costPerOunce1) 
: senderName(senderName1),recipientName(recipientName1),address(address1),city(city1),state(state1),postalCode(postalCode1),weight(weight1),costPerOunce(costPerOunce1)
{
	if(weight1>0)
	{
		weight=weight1;	
	}
	else
	{
		weight=1;
		cout << "Weight less than 0 !" << endl;
	}	
} 
double Package::calculateCost() const 
{
	double transCosts;
	transCosts=weight*costPerOunce;
	return transCosts;
}
double Package::getWeight() const
{
	return weight;
}
double Package::getCostPerOunce() const 
{
	return costPerOunce;
}

5.TwoDayPackage构造函数接受一个值来初始化数据成员。并重新定义基类的成员函数calculateCost来计输费用，具体方法将平寄费加到基类Package的 calculateCost函数计算得到的基于重量的费用中。

TwoDayPackage::TwoDayPackage(const string& senderName1,const string& recipientName1, const string& address1, const string& city1,const string& state1,int postalCode1, double weight1, double costPerOunce1,double surfaceMailCosts1)
:Package(senderName1,recipientName1,address1,city1,state1,postalCode1,weight1,costPerOunce1)
{																							
	surfaceMailCosts=surfaceMailCosts1; 										
}
double TwoDayPackage::calculateCost() const
{
	double transCosts;
	
	transCosts = Package::calculateCost()  + surfaceMailCosts;
	
	return transCosts;
}

6.类 OvernightPackage重新定义基类的成员函数calculateCost来使它在计算运输费用之前,先将额外每盎司费用加到标准的每盎司费用上。

OvernightPackage::OvernightPackage(const string& senderName1,const string& recipientName1, const string& address1, const string& city1,const string& state1,int postalCode1, double weight1, double costPerOunce1,double extraCosts1)
:Package(senderName1,recipientName1,address1,city1,state1,postalCode1,weight1,costPerOunce1)
{
	extraCosts=extraCosts1; 
}	
double OvernightPackage::calculateCost() const
{
	double transCosts;
	
	transCosts = Package::calculateCost()  + extraCosts;
	
	return transCosts;	
}

7.编写测试程序，创建每种Package的对象并测试成员函数 calculateCost。

//测试程序 
int main()
{	
	Package text1("Lihua","Kandy","America","NewYork","NewYorkState",10041,30,5) ;
	cout << "The cost of a regular package is ：" << text1.calculateCost() << endl;
	cout << endl;
	TwoDayPackage text2("Zhang shan","Kandy","America","Houston","Texas",77001,50,8,25.6); 
	cout << "The cost of two-day package is   : " << text2.calculateCost() << endl;
	cout << endl;
	OvernightPackage text3("","Kandy","America","St. Paul","Minnesota",35350,25,4,36.5);
	cout << "The cost of overnight package is : " << text3.calculateCost() << endl;
	cout << endl;
	return 0;
}

完整代码如下：

/
//Package继承层次.cpp 
/
#include<iostream>
#include<string>
using namespace std;
class Package
{
	public://声明为常量引用，使用引用避免copy，使用const能保护数据 
		Package(const string&,	const string&, const string&, const string&,const string&, int , double , double);
		double calculateCost() const;
		double getWeight() const;
		double getCostPerOunce() const;
	private:
		string senderName;		
		string recipientName;
		string address;
		string city;
		string state;
		int postalCode;
		double weight;
		double costPerOunce;//Cost per ounce每一盎司费用 ；盎司：英美制单位，既是重量单位又是容量单位 
};
class TwoDayPackage : public Package
{
	public:
		TwoDayPackage(const string&, const string&, const string&, const string&,const string&, int , double , double, double);
		double calculateCost() const;//基类的成员函数需要在派生类内声明才可被使用 
	private:
		double surfaceMailCosts;//平寄费 
};
class OvernightPackage : public Package
{
	public:
		OvernightPackage(const string&, const string&, const string&, const string&,const string&, int , double , double, double);
		double calculateCost() const;
	private:
		double extraCosts;//连夜快递服务的额外费用 
};
Package::Package(const string& senderName1,const string& recipientName1, const string& address1, const string& city1,const string& state1,int postalCode1, double weight1, double costPerOunce1) 
: senderName(senderName1),recipientName(recipientName1),address(address1),city(city1),state(state1),postalCode(postalCode1),weight(weight1),costPerOunce(costPerOunce1)
{
	if(weight1>0)
	{
		weight=weight1;	
	}
	else
	{
		weight=1;
		cout << "Weight less than 0 !" << endl;
	}	
} 
double Package::calculateCost() const 
{
	double transCosts;
	transCosts=weight*costPerOunce;
	return transCosts;
}
double Package::getWeight() const
{
	return weight;
}
double Package::getCostPerOunce() const 
{
	return costPerOunce;
}


TwoDayPackage::TwoDayPackage(const string& senderName1,const string& recipientName1, const string& address1, const string& city1,const string& state1,int postalCode1, double weight1, double costPerOunce1,double surfaceMailCosts1)
:Package(senderName1,recipientName1,address1,city1,state1,postalCode1,weight1,costPerOunce1)
{																							
	surfaceMailCosts=surfaceMailCosts1; 										
}
double TwoDayPackage::calculateCost() const
{
	double transCosts;
	
	transCosts = Package::calculateCost()  + surfaceMailCosts;
	
	return transCosts;
}

OvernightPackage::OvernightPackage(const string& senderName1,const string& recipientName1, const string& address1, const string& city1,const string& state1,int postalCode1, double weight1, double costPerOunce1,double extraCosts1)
:Package(senderName1,recipientName1,address1,city1,state1,postalCode1,weight1,costPerOunce1)
{
	extraCosts=extraCosts1; 
}	
double OvernightPackage::calculateCost() const
{
	double transCosts;
	
	transCosts = Package::calculateCost()  + extraCosts;
	
	return transCosts;	
}
//测试程序 
int main()
{	
	Package text1("Lihua","Kandy","America","NewYork","NewYorkState",10041,30,5) ;
	cout << "The cost of a regular package is ：" << text1.calculateCost() << endl;
	cout << endl;
	TwoDayPackage text2("Zhang shan","Kandy","America","Houston","Texas",77001,50,8,25.6); 
	cout << "The cost of two-day package is   : " << text2.calculateCost() << endl;
	cout << endl;
	OvernightPackage text3("","Kandy","America","St. Paul","Minnesota",35350,25,4,36.5);
	cout << "The cost of overnight package is : " << text3.calculateCost() << endl;
	cout << endl;
	return 0;
}