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Pointers, Arrays and Creating Objs...

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Join Date: Nov 2008

Posts: 29

Reputation: Lokolo is an unknown quantity at this point

Solved Threads: 1

Lokolo

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Pointers, Arrays and Creating Objs...

Nov 7th, 2008

Btw below is the key parts of my code - not all as there are loads of lines:

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//main.cpp
#include <iostream>
#include "Customer.h"
 
using namespace std;
 
void displayMainMenu();
int enterMainChoice();
void displayAccountMenu();
int enterAccountChoice();
int enterCustomerID();
Customer createCustomer();
 
void main(void)
{
	unsigned short numberOfCustomers = 0;
	Customer *Customers[10];
 
	*Customers[numberOfCustomers] = createCustomer();
	numberOfCustomers++;
}
 
Customer createCustomer()
{
	string name;
	int age;
	cout << "\nPlease enter you name: ";
	cin >> name;
	cout << "Please enter you age: ";
	cin >> age;
	return Customer(name, age);
}
//main.cpp
#include <iostream>
#include "Customer.h"

using namespace std;

void displayMainMenu();
int enterMainChoice();
void displayAccountMenu();
int enterAccountChoice();
int enterCustomerID();
Customer createCustomer();

void main(void)
{
	unsigned short numberOfCustomers = 0;
	Customer *Customers[10];

	*Customers[numberOfCustomers] = createCustomer();
	numberOfCustomers++;
}

Customer createCustomer()
{
	string name;
	int age;
	cout << "\nPlease enter you name: ";
	cin >> name;
	cout << "Please enter you age: ";
	cin >> age;
	return Customer(name, age);
}

----------------
Below is just the main function from Customer.cpp
----------------

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Customer::Customer(string name, int age)
{
	this->name = name;
	this->age = age;
}
Customer::Customer(string name, int age)
{
	this->name = name;
	this->age = age;
}

Now it almost works. I can run it and it asks me for the information, but when it tries to add the actual customer is crashes in "xstring" with this error:

Unhandled exception at 0x643924f0 (msvcp90d.dll) in bankusingarrays.exe: 0xC0000005: Access violation reading location 0xcccccce8.

Now - I thought it would be because I am passing back something which can't be then put into the pointer array.

But I am not sure how to go about it - trying to create the object and store the address in the pointer array. I am pretty new with C++ so try and bare with me lol..

Thanks!

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Join Date: Nov 2008

Posts: 81

Reputation: minas1 is an unknown quantity at this point

Solved Threads: 8

minas1

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Re: Pointers, Arrays and Creating Objs...

Nov 7th, 2008

 Help with Code Tags 
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Customer *Customers[10];
Customer *Customers[10];

You create an array of pointers to that object.

Why don't you do:

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Customer Customers[10];
Customer[numberOfCustomers] = createCustomer();
Customer Customers[10];
Customer[numberOfCustomers] = createCustomer();

-------------

1.Basically you are misuing pointers. In C and C++, when a variable is uninitialized, it contains a garbage value. Thus, Customers from 0 to 9 point to garbage values. They are pointers, which means they point in unknown places in the memory.

Then, you are assigning a value to that unknown memory location. This is the error. Before assigning, you have to be sure that the pointer points to a valid memory location of that object.
This is what you are doing.

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int main()
{
	int *p, x;
 
	x = 10;
	*p = x;
}
int main()
{
	int *p, x;

	x = 10;
	*p = x;
}

This is what you should be doing.

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int main()
{
	int *p, x;
 
	x = 10;
	p = &x;
}
int main()
{
	int *p, x;

	x = 10;
	p = &x;
}

If you still want an array of pointers to Customer objects, you should write:

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Customers[numberOfCustomers] = &(createCustomer()); //the address of the object
Customers[numberOfCustomers] = &(createCustomer()); //the address of the object

2.
Don't use void main(void). Just int main(). The use of void in the parentheses is redundant. It is required in C but not in C++.

Last edited by minas1; Nov 7th, 2008 at 1:49 pm.

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Join Date: Feb 2008

Posts: 114

Reputation: sidatra79 is an unknown quantity at this point

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sidatra79

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Junior Poster

Re: Pointers, Arrays and Creating Objs...

Nov 7th, 2008

Hi
could u please post the Customer.h too?

"What we repeat defines what we are!!" Aristotle
-->
"looping.. defines Perfomance from O (n) ..up to O(n!)" Sidatra79 :D :D

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Join Date: Nov 2008

Posts: 29

Reputation: Lokolo is an unknown quantity at this point

Solved Threads: 1

Lokolo

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Re: Pointers, Arrays and Creating Objs...

Nov 7th, 2008

•

Originally Posted by sidatra79

Hi
could u please post the Customer.h too?

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#include <string>
#pragma once
 
using namespace std;
//----------------------
class Customer
{
 
private:
	string name;
	int age;
 
public:
 
	//builder
	Customer(string name, int age);
 
	//operations
	void Display();
};
#include <string>
#pragma once

using namespace std;
//----------------------
class Customer
{

private:
	string name;
	int age;

public:
	
	//builder
	Customer(string name, int age);

	//operations
	void Display();
};

the display function doesn't have anything it btw, thats for later

•

Originally Posted by minas1

...

Ok thanks dude, briefly looking at it makes total sense, will look over my code to do as you say!

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Join Date: Feb 2008

Posts: 114

Reputation: sidatra79 is an unknown quantity at this point

Solved Threads: 8

sidatra79

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Junior Poster

Re: Pointers, Arrays and Creating Objs...

Nov 7th, 2008

Hi again,
have a look on this it might help u:

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#include <string>
#include <iostream>
 
using namespace std;
 
const int MAX_NO_OF_CUSTOMERS = 3;
 
class Customer
{
private:
	string name;
	int age;
	static unsigned short numberOfCustomers;
public:
	Customer()
	{
		createCustomer();	
		numberOfCustomers++;
	}
 
	Customer(string name, int age)
	{
		this->name = name;
		this->age = age;	
	}
 
	Customer createCustomer()
	{
		string name;
		int age;
		cout << "\nPlease enter you name: ";
		cin >> name;
		cout << "Please enter you age: ";
		cin >> age;
		return Customer(name, age);	
	}
	int getNumberofCustomers()
	{
		return numberOfCustomers;
	}
};
unsigned short Customer::numberOfCustomers = 0;
 
 
int main()
{
	int customersInTotal;
	Customer *Customers = new Customer[MAX_NO_OF_CUSTOMERS];
	customersInTotal=Customers->getNumberofCustomers();
	cout<<"Until now "<<customersInTotal<<" customers have been added."<<endl;
	return 0;
}
#include <string>
#include <iostream>

using namespace std;

const int MAX_NO_OF_CUSTOMERS = 3;

class Customer
{
private:
	string name;
	int age;
	static unsigned short numberOfCustomers;
public:
	Customer()
	{
		createCustomer();	
		numberOfCustomers++;
	}

	Customer(string name, int age)
	{
		this->name = name;
		this->age = age;	
	}

	Customer createCustomer()
	{
		string name;
		int age;
		cout << "\nPlease enter you name: ";
		cin >> name;
		cout << "Please enter you age: ";
		cin >> age;
		return Customer(name, age);	
	}
	int getNumberofCustomers()
	{
		return numberOfCustomers;
	}
};
unsigned short Customer::numberOfCustomers = 0;


int main()
{
	int customersInTotal;
	Customer *Customers = new Customer[MAX_NO_OF_CUSTOMERS];
	customersInTotal=Customers->getNumberofCustomers();
	cout<<"Until now "<<customersInTotal<<" customers have been added."<<endl;
	return 0;
}

i did on a hurry....maybe there are big mistakes

However it compiles and runs...

P.S: keep this in mind:
A no-argument constructor will be called automatically when dealing with an array of objects. But when u define some constructor with arguments, then u need to define a no-argument constructor too.

Last edited by sidatra79; Nov 7th, 2008 at 3:52 pm. Reason: added sth

"What we repeat defines what we are!!" Aristotle
-->
"looping.. defines Perfomance from O (n) ..up to O(n!)" Sidatra79 :D :D