应该是虚拟析构函数吗?但是怎么做呢?

一个程序，用于将电话公司的消费者数据存储在链表中。最后，它显示每个人的账单。我有以下代码：

class BaseTypeOfContract
{
private:
int minutePrice;
int SMSPrice;
public:
void setminutePrice(int x) { minutePrice = x; }
void setSMSPrice(int x) { SMSPrice = x; }
virtual int calculateBill(int talkedMinutes, int sentSMS) = 0;
int getminutePrice() const { return minutePrice; }
int getSMSPrice() const { return SMSPrice; }
};

class SMSBaseType : public BaseTypeOfContract
{
private:
int freeSMS;
public:
SMSBaseType(int minutePrice, int SMSPrice, int freeSMS)
{
setminutePrice(minutePrice);
setSMSPrice(SMSPrice);
setfreeSMS(freeSMS);
}
public:
void setfreeSMS(int free) { this->freeSMS = free; }
virtual int calculateBill(int talkedMinutes, int sentSMS)
{
int billedSMS = (freeSMS > sentSMS) ? 0 : sentSMS - freeSMS;
return talkedMinutes * getminutePrice() + billedSMS * getSMSPrice();
}
};
class Base : public BaseTypeOfContract
{
public:
Base()
{
setminutePrice(30);
setSMSPrice(10);
}
virtual int calculateBill(int talkedMinutes, int sentSMS) { return talkedMinutes * getminutePrice() + sentSMS * getSMSPrice();}
};
class SMSMax : public SMSBaseType
{
public:
SMSMax() : SMSBaseType(20, 5, 150) {}
};
class MobiNET: public SMSBaseType
{
public:
MobiNET() : SMSBaseType(10, 15, 25) {}
};

客户类：

class Client
{
public:
std::string name;
std::string phoneNumber;
BaseTypeOfContract* typeOfContract;
int talkedMinutes;
int sentSMS;
Client *next;
public:
Client(){}
Client(std::string n, std::string p, int bp, int ks) : name(n), phoneNumber(p), talkedMinutes(bp), sentSMS(ks) {}

void preSetPlan(std::string s)
{
if (s == "MobiNET")
this->typeOfContract = new MobiNET();
else if (s == "SMSMax")
this->typeOfContract = new SMSMax();
else this->typeOfContract = new Base();
}
std::string getname() const { return name; }
std::string getphoneNumber() const { return phoneNumber; }
void setname(std::string n) { name = n; }
void setphoneNumber(std::string pn) { phoneNumber = pn; }
void settalkedMinutes(int bp) { talkedMinutes = bp; }
void setsentSMS(int SSMS) { sentSMS = SSMS; }
int getBill() const { return this->typeOfContract->calculateBill(talkedMinutes, sentSMS); }
};

我从 2 个文件中读取了数据。第一个文件包含姓名，电话号码，合同类型。第二个文件包含电话号码，通话记录和发送的短信。

Client* file_read_in()
{
std::ifstream ClientData;
ClientData.open("clients.txt");
Client *first = new Client;
first = NULL;
while (!ClientData.eof())
{
std::string name, phoneNumber, typeOfContract;
ClientData >> name;
ClientData >> phoneNumber;
ClientData >> typeOfContract;
std::ifstream ClientTalkedSent;
ClientTalkedSent.open("used.txt");
while(!ClientTalkedSent.eof())
{
std::string phoneNumber2;
ClientTalkedSent >> phoneNumber2;
if (phoneNumber2 == phoneNumber)
{
int talkedMinutes, sentSMS;
ClientTalkedSent >> talkedMinutes;
ClientTalkedSent >> sentSMS;
Client* tmp = new Client(name, phoneNumber, talkedMinutes, sentSMS);
tmp->preSetPlan(typeOfContract);
tmp->next = NULL;
if (first == NULL)
{
first = tmp;
}
else
{
Client *cond = first;
while (cond->next != NULL) cond = cond->next;
cond->next = tmp;
}
}
}
ClientTalkedSent.close();
}
ClientData.close();
return first;
}

而主要的：

int main()
{
Client* first = file_read_in();
while(first != NULL)
{
std::cout << first->getname() << " " << first->getphoneNumber() << " " << first->getBill() << std::endl;
first = first->next;
}
return 0;
}

我的问题是我应该释放分配的内存，但我想知道如何。哪个类的析构函数应该做脏工作。如果有人可以使用我的代码来展示"析构函数继承"的工作原理，我将不胜感激。

对不起，我的英语不好，谢谢你的帮助。这个网站帮助了我很多次，但对于这个问题我没有找到解决方案。