Polymorphism question in a C++ example

[scarebyte]

Hi guys,

I have a question concerning the following code I have written for a final project in an entry level C++ course. My task requires 3 level hierarchy (which i have) and use of polymorphism. The program works in this state, but I dont think I am actually exercising any polymorphic function and I am struggling to do it correctly. Various errors like C2228 or C2227 appear when I try to call a virtual function through an object.
I am not very experienced, that's why I am asking for your help.

Btw, this is like a toolkit for table booking and bill processing in a restaurant for example.

10X in advance!

#include <cstdlib>
#include <iostream>
#include <vector>
#include <string>
#include <iomanip>
#include <fstream>
using namespace std;
struct Menu
{
	int soup,salad, beefsteak, pizza, pancake, cake, soda, whisky;
};
class Client 
{
public:
	string name;
	Menu order;
	int table_number;
	string type;
	double bill;
	
	Client(void)
	{
		name="";
		table_number=0;
		type="";
		bill=0.0;
	}
};

int tables_booked[20];
Client clients[20];
int number_clients;


class Table:public Client
{
public:
	
	Table(void)
	{
		number_clients=0;
	}

	virtual void addClient(void)
	{
		clients[number_clients].order.soup=0;
		clients[number_clients].order.salad=0;
		clients[number_clients].order.beefsteak=0;
		clients[number_clients].order.pizza=0;
		clients[number_clients].order.pancake=0;
		clients[number_clients].order.cake=0;
		clients[number_clients].order.soda=0;
		clients[number_clients].order.whisky=0;
		cout<<"\nEnter client's name:";
		cin>>clients[number_clients].name;
	}

	void ShowList(void)
	{
		cout<<"________________________________________________________________________________";
		cout<<"\nNumber    Name                        Table number         Bill      Type";
		for (int i=0;i<number_clients;i++)
		{
			cout<<"\n"<<setw(3)<<i<<setw(30)<<clients[i].name<<setw(15)<<clients[i].table_number<<setw(15)<<clients[i].bill<<setw(12)<<clients[i].type<<endl;
		}
		system("pause"); 
	}
	
	virtual void addBill(void)
	{
		int m,choice=0,quantity=0;
		do
		{
			ShowList();
			cout<<"\nEnter client's number according to the list:";
			cin>>m;
			if ((m<0)||(m>=number_clients))
			{
				cout<<"\nNo such number in the list...Try again.";
				system("pause");
			}
		}

		while ((m<0)||(m>=number_clients));
		cout <<"\nWhat did the client order from the menu?";
		cout<<"\n0.Soup";
		cout<<"\n1.Salad";
		cout<<"\n2.Beefsteak";
		cout<<"\n3.Pizza";
		cout<<"\n4.Pancake";
		cout<<"\n5.Cake";
		cout<<"\n6.Soda";
		cout<<"\n7.Whisky";
		cout<<"\nEnter: 0,1,2,3,4,5,6 or 7:";
		do{
			cin>>choice;
			if ((choice<0)||(choice>7)) 
			{
				cout<<"\nInvalid choice. Try again.";
				system("pause");
			}
		}
		while ((choice<0)||(choice>7));
		switch (choice)
		{
		case 0:
			{
				cout<<"\nEnter quantity:";
				cin>>quantity;				
				clients[m].bill+=quantity*4;
				cout<<"\n"<<quantity*4<<" lv. were added to the bill of "<<clients[m].name<<".";
				system("pause");
			}
			break;
		case 1:
			{
				cout<<"\nEnter quantity:";
				cin>>quantity;
				clients[m].bill+=quantity*6;
				cout<<"\n"<<quantity*6<<" lv. were added to the bill of "<<clients[m].name<<".";
				system("pause");
			}
			break;
		case 2:
			{
				cout<<"\nEnter quantity:";
				cin>>quantity;					
				clients[m].bill+=quantity*15;
				cout<<"\n"<<quantity*15<<" lv. were added to the bill of "<<clients[m].name<<".";
				system("pause");
			}
			break;
		case 3:
			{
				cout<<"\nEnter quantity:";
				cin>>quantity;
				clients[m].bill+=quantity*10;
				cout<<"\n"<<quantity*10<<" lv. were added to the bill of "<<clients[m].name<<".";
				system("pause");
			}
			break;
		case 4:
			{
				cout<<"\nEnter quantity:";
				cin>>quantity;
				clients[m].bill+=quantity*3;
				cout<<"\n"<<quantity*3<<" lv. were added to the bill of "<<clients[m].name<<".";
				system("pause");
			}
			break;
		case 5:
			{	
				cout<<"\nEnter quantity not greater than :";
				cin>>quantity;
				clients[m].bill+=quantity*4;
				cout<<"\n"<<quantity*4<<" lv. were added to the bill of "<<clients[m].name<<".";
				system("pause");
			}
			break;
		case 6:
			{
				cout<<"\nEnter quantity:";
				cin>>quantity;	
				clients[m].bill+=quantity*2;
				cout<<"\n"<<quantity*2<<" lv. were added to the bill of "<<clients[m].name<<".";
				system("pause");
			}
			break;                          
		case 7:
			{
				cout<<"\nEnter quantity:";
				cin>>quantity;
				clients[m].bill+=quantity*15;
				cout<<"\n"<<quantity*15<<" lv. were added to the bill of "<<clients[m].name<<".";
				system("pause");
			}
			break;  
		}
}

void RemoveFromList(void)
{
	ShowList();
	int list;
	do{
		cout<<"\nEnter client's number to be removed from the list:";cin>>list;
		if ((list<0)||(list>=number_clients))
		{
			cout<<"\nNu such number in the list...Try again:";
			system("pause");
		}
	}
	while   ((list<0)||(list>=number_clients));
	string name=clients[list].name;
	if (list==number_clients-1)
	{
		clients[list].type="";
		clients[list].bill=0;
		clients[list].order.soup=0;
		clients[list].order.salad=0;
		clients[list].order.beefsteak=0;
		clients[list].order.pizza=0;
		clients[list].order.pancake=0;
		clients[list].order.cake=0;
		clients[list].order.soda=0;
		clients[list].order.whisky=0;
	}
	else{
		for (int i=list;i<number_clients;i++)
		{
			clients[i].name=clients[i+1].name;
			clients[i].table_number=clients[i+1].table_number;
			clients[i].type=clients[i+1].type;
			clients[i].bill=clients[i+1].bill;
			clients[i].order.soup=clients[i+1].order.soup;
			clients[i].order.salad=clients[i+1].order.salad;
			clients[i].order.beefsteak=clients[i+1].order.beefsteak;
			clients[i].order.pizza=clients[i+1].order.pizza;
			clients[i].order.pancake=clients[i+1].order.pancake;
			clients[i].order.cake=clients[i+1].order.cake;
			clients[i].order.soda=clients[i+1].order.soda; 
			clients[i].order.whisky=clients[i+1].order.whisky;
		}  
	}
	cout<<"\n"<<name<<" was successfully deleted from the list.";
	system ("pause");
	tables_booked[list]=0;  
	number_clients--;
}   

void ReadFromFile(void)
{         
	ifstream ifile("restaurant.txt");
	ifile>>number_clients;
	int table;
	for (int i=0;i<number_clients;i++)
	{
		ifile>>clients[i].name;
		ifile>>clients[i].table_number;
		ifile>>clients[i].type;
		ifile>>clients[i].bill;
		ifile>>clients[i].order.soup;
		ifile>>clients[i].order.salad;
		ifile>>clients[i].order.beefsteak;
		ifile>>clients[i].order.pizza;
		ifile>>clients[i].order.pancake;
		ifile>>clients[i].order.cake;
		ifile>>clients[i].order.soda;
		ifile>>clients[i].order.whisky;
		table=clients[i].table_number;
		tables_booked[table]=1;
	}
	ifile.close(); 
}

void WriteToFile(void)
{
	ofstream ofile("restaurant.txt");
	ofile<<number_clients<<"\n";
	for (int i=0;i<number_clients;i++)
	{
		ofile<<clients[i].name<<"\n";
		ofile<<clients[i].table_number<<"\n";
		ofile<<clients[i].type<<"\n";
		ofile<<clients[i].bill<<"\n";
		ofile<<clients[i].order.soup<<"\n";
		ofile<<clients[i].order.salad<<"\n";
		ofile<<clients[i].order.beefsteak<<"\n";
		ofile<<clients[i].order.pizza<<"\n";
		ofile<<clients[i].order.pancake<<"\n";
		ofile<<clients[i].order.cake<<"\n";
		ofile<<clients[i].order.soda<<"\n";
		ofile<<clients[i].order.whisky<<"\n";
	}
	ofile.close();  
} 
};

class One:public Table
{
private:
	void addClient(void)
	{
		Table::addClient();
		int table;
		do {
			cout<<"\nEnter table number between 1-4:";
			cin>>table;
			if(tables_booked[table]==1) 
			{
				cout<<"\nThe table is booked. Try again:";
				system("pause");
			}
			if((table<1)||(table>4)) 
			{
				cout<<"\nInvalid table number. Try again:";
				system("pause");
			}
		}
		while ((tables_booked[table]==1)||(table<1)||(table>4));
		cout<<"\n"<<clients[number_clients].name<<" was successfully added to the list.";
		system("pause");
		number_clients++;
	}
	
	virtual void addBill(void)
	{
		Table::addBill();
	}
	
};

class Two:public Table
{
private:
	void addClient(void)
	{
		Table::addClient();
		int table;
		do {
			cout<<"\nEnter table number between 5-10:";
			cin>>table;
			if(tables_booked[table]==1) 
			{
				cout<<"\nThe table is booked. Try again:";
				system("pause");
			}
			if((table<5)||(table>10))
			{
				cout<<"\nInvalid table number. Try again:";
				system("pause");
			}
		}
		while ((tables_booked[table]==1)||(table<5)||(table>10));
		cout<<"\n"<<clients[number_clients].name<<" was successfully added to the list.";
		system("pause");
		number_clients++;
	}

	virtual void addBill(void)
	{
		Table::addBill();
	}
};

class Up_to_6:public Table
{
private:
	void addClient(void)
	{
		Table::addClient();
		int table;
		do {
			cout<<"\nEnter table number between 11-17:";
                     cin>>table;
                     if(tables_booked[table]==1) 
					 {
						 cout<<"\nThe table is booked. Try again:";
						 system("pause");
					 }
					 if((table<11)||(table>17))
					 {
						 cout<<"\nInvalid table number. Try again:";
						 system("pause");
					 }
		}
		while ((tables_booked[table]==1)||(table<11)||(table>17));		
		cout<<"\n"<<clients[number_clients].name<<" was successfully added to the list.";
		system("pause");
		number_clients++;
	}

	virtual void addBill(void)
	{
		Table::addBill();
	}
};

class moreThan_6:public Table
{
private:
	void addClient(void)
	{
		Table::addClient();
		int table;
		do {
			cout<<"\nEnter table number between 18-20:";
			cin>>table;
			if(tables_booked[table]==1) 
			{
				cout<<"\nThe table is booked. Try again:";
				system("pause");
			}
			if((table<18)||(table>20)) 
			{
				cout<<"\nInvalid table number. Try again:";
				system("pause");
			}
		}
		while ((tables_booked[table]==1)||(table<18)||(table>20));		
		cout<<"\n"<<clients[number_clients].name<<" successfully added to the list.";
		system("pause");
		number_clients++;
	}

	virtual void addBill(void)
	{
		Table::addBill();
	}
};

void ProgramMenu(void)
{
	int choice;
	One aOne;
	Table *aOneTable=&aOne;
	Two aTwo;
	Table *aTwoTable=&aTwo;
	Up_to_6 aUp_to_6;
	Table *aUp_to_6Table=&aUp_to_6;
	moreThan_6 amoreThan_6;
	Table *amoreThan_6Table=&amoreThan_6;
	aOneTable->ReadFromFile();
up:
	do{
		cout<<"\n________________________________________________________________________________";
		cout<<"\n1.Reserve a table for one.";
		cout<<"\n2.Reserve a table for two.";
		cout<<"\n3.Reserve a table for up to 6 people .";
		cout<<"\n4.Reserve a table for more than 6 people.";
		cout<<"\n5.Display the list of clients.";
		cout<<"\n6.Process client's orders to their bills.";
		cout<<"\n7.Delete client from the list.";
		cout<<"\n8.Save changes and exit.";
		cout<<"\n________________________________________________________________________________";
		cout<<"\nEnter your choice:";
		cin>>choice;
		if((choice<1)||(choice>8))
		{
			cout<<"\nInvalid choice entered.Try again:";
			system("pause");
		}
	}while ((choice<1)||(choice>8));
     switch (choice)
	 {
	 case 1:{
		 aOneTable->addClient();
		 goto up;
			}
			break;
	 case 2:{
		 aTwoTable->addClient();
		 goto up;
			}
			break;
	 case 3:{
		 aUp_to_6Table->addClient();
		 goto up;
			}
			break;
	 case 4:{
		 amoreThan_6Table->addClient();
		 goto up;
			}
			break;
	 case 5:{
		 aOneTable->ShowList();
		 goto up;
			}
			break;
	 case 6:{
		 aOneTable->addBill();
		 goto up;
			}
			break;
	 case 7:{
		 aOneTable->RemoveFromList();
		 goto up;}
			break;
	 case 8:
		 aOneTable->WriteToFile();
		 break;
	 }
}   

int main(int argc, char *argv[])
{	
	cout<<"\n\t\tWelcome to the Table Booking and Bill Making Toolkit !!!"<<endl;
	ProgramMenu();
	system("PAUSE");
	return EXIT_SUCCESS;
}

[Clockowl]

class Client 
{
public:
	string name;
	Menu order;
	int table_number;
	string type;
	double bill;
	
	Client(void)
	{
		name="";
		table_number=0;
		type="";
		bill=0.0;
	}
};

This code lacks the virtual addClient table wants to use. Another note: is a table a client? If not, you shouldn't have inheritance, but perhaps composition.

[scarebyte]

Well i know Table fails the "is-a" test for inheritance, but as i said this i an entry course in C++ and the professor wont consider this, as we have a requirement to have 3 level hierarchy. If the hierarchy provided works it's fine.

[jencas]

Either the Client ctor lacks the initialization of order or Menu lacks an appropriate ctor

[ArkM]

Cascades of monstrous data moving... have you ever heard about operator= in C++?

clients[i] = clients[i+1];

instead of awful (quote):

clients[i].name=clients[i+1].name;
clients[i].table_number=clients[i+1].table_number;
clients[i].type=clients[i+1].type;
clients[i].bill=clients[i+1].bill;
clients[i].order.soup=clients[i+1].order.soup;
clients[i].order.salad=clients[i+1].order.salad;
clients[i].order.beefsteak=clients[i+1].order.beefsteak;
clients[i].order.pizza=clients[i+1].order.pizza;
clients[i].order.pancake=clients[i+1].order.pancake;
clients[i].order.cake=clients[i+1].order.cake;
clients[i].order.soda=clients[i+1].order.soda; 
clients[i].order.whisky=clients[i+1].order.whisky;

That famous system("pause") after prompt "Try again" ???
It seems no once input result check in the program (it's so simple)

if (!(cin >> choice)) { // not a number entered
   cout << "Not a number, try again...\n";
   cin.clear();
   cin.ignore(1000,'\n');
   continue;
}

Death sentence: there are gotos in switch statements...

I can't imagine that this program is capable to do anything...

Next time use code tag properly:
[code=cplusplus] sources

[/code]

[scarebyte]

Ok, I am pretty much sure there is plenty to be corrected and optimized. But that is not what i am asking. I just wanted to see if someone can give me a suggestion on how to implement polymorphism in this example. As you see in every 3-rd level class from the hierarchy, at the end i call this function:

virtual void addBill(void)
	{
		Table::addBill();
	}

but in this way, using the scope operator, i am not exercising any virtual functions.

[Clockowl]

Example of inheritance using virtual functions:

#include <iostream>
using namespace std;

class base {
    public:
    virtual void func(){
        cout << "First level: Base class" << endl;
    }
};

class der1 : public base {
    public:
    virtual void func(){
        cout << "Second level: Derived class" << endl;
    }
};

class der2 : public der1 {
    public:
    virtual void func(){
        cout << "Third level: Second derived class" << endl;
    }
};

int main(){
    base* all_your_base[3] = {new base, new der1, new der2};

    for(int n = 0; n < 3; n++){
        all_your_base[n]->func();
    }

    return 0;
}

[scarebyte]

Thank you Clockowl, and everyone else who took part. I managed to solve apply polymorphism on the given example. Problem solved