Managed C++ Tutorials - Array-Based Lists

	Array-Based Lists

Introduction

A list is a collection of items of the same kind. The list can be based of number (natural or floating-point), text, dates, times, or such values as long as the items are of the same type. Lists are at the core of computer programming. There are used in databases, spreadsheets, word processors and applications that are not primarily list-oriented.

We are going to create a list of double-precision numbers.

List Setup

There are various ways to create a list. We will take a look at the simplest approach, which is to use a normal array. With this technique, you can start by creating a class. Here is an example:

Header File: listofnumbers.h

#pragma once

//---------------------------------------------------------------------------
public __gc class CListOfNumbers
{
public:
	CListOfNumbers(void);
	virtual ~CListOfNumbers(void);
};
//---------------------------------------------------------------------------

Source Code: listofnumbers.cpp

#include "StdAfx.h"
#include ".\listofnumbers.h"
#using <mscorlib.dll>

//---------------------------------------------------------------------------
CListOfNumbers::CListOfNumbers(void)
{
}
//---------------------------------------------------------------------------
CListOfNumbers::~CListOfNumbers(void)
{
}
//---------------------------------------------------------------------------

To start the list, you can declare an array as a member variable:

Header File: listofnumbers.h

#pragma once

const int MaxItems = 20;
//---------------------------------------------------------------------------
public __gc class CListOfNumbers
{
private:
	System::Double Item[];

public:
	CListOfNumbers(void);
	virtual ~CListOfNumbers(void);
};
//---------------------------------------------------------------------------

Since we are going to use a managed array, you can initialize it as follows:

Source Code: listofnumbers.cpp

#include "StdAfx.h"
#include ".\listofnumbers.h"
#using <mscorlib.dll>

//---------------------------------------------------------------------------
CListOfNumbers::CListOfNumbers(void)
{
	Item = new System::Double[MaxItems];
}
//---------------------------------------------------------------------------
CListOfNumbers::~CListOfNumbers(void)
{
}
//---------------------------------------------------------------------------

A primary accessory you need when using a list is a count of the number of items in the list when they are added or deleted. This accessory is primarily a private member variable as a simple natural number:

Header File: listofnumbers.h

#pragma once

const int MaxItems = 20;
//---------------------------------------------------------------------------
public __gc class CListOfNumbers
{
private:
	System::Double Item[];

public:
	CListOfNumbers(void);
	virtual ~CListOfNumbers(void);
	int Size;
};
//---------------------------------------------------------------------------

When the class is declared, this member variable should be set to 0 to indicate that the list is primarily empty:

Source Code: listofnumbers.cpp

#include "StdAfx.h"
#include ".\listofnumbers.h"
#using <mscorlib.dll>

//---------------------------------------------------------------------------
CListOfNumbers::CListOfNumbers(void)
    : Size(0)
{
	Item = new System::Double[MaxItems];
}
//---------------------------------------------------------------------------
CListOfNumbers::~CListOfNumbers(void)
{
}
//---------------------------------------------------------------------------

Since the Size member variable was declared private, if you plan to get the count of items in the list from outside the class, you should provide a method as interface. This can simply be done as follows:

Header File: listofnumbers.h

#pragma once

const int MaxItems = 20;
//---------------------------------------------------------------------------
class CListOfNumbers
{
private:
	double Item[MaxItems];
	int Size;

public:
	int Count() const;
	CListOfNumbers();
	virtual ~CListOfNumbers();
};
//---------------------------------------------------------------------------

Source Code: listofnumbers.cpp

#include "StdAfx.h"
#include ".\listofnumbers.h"
#using <mscorlib.dll>

//---------------------------------------------------------------------------
CListOfNumbers::CListOfNumbers(void)
	: Size(0)
{
	Item = new System::Double[MaxItems];
}
//---------------------------------------------------------------------------
CListOfNumbers::~CListOfNumbers(void)
{
}
//---------------------------------------------------------------------------
// Provides the current number of items in the list
int CListOfNumbers::Count(void)
{
	return Size;
}
//---------------------------------------------------------------------------

This method can help you get the number of items in the list anytime. Here is an example:

Source Code: Exercise.cpp

// This is the main project file for VC++ application project 
// generated using an Application Wizard.

#include "stdafx.h"
#include ".\listofnumbers.h"

#using <mscorlib.dll>

using namespace System;

int _tmain()
{
    // TODO: Please replace the sample code below with your own.
    CListOfNumbers *List = __gc new CListOfNumbers;

    Console::WriteLine(S"Current Number of Items: {0}", __box(List->Count()));

    Console::WriteLine(S"");
    return 0;
}

This would produce:

Current Number of Items: 0
Press any key to continue

Item Addition

Creating a list consists of adding items to it. Items are usually added one at a time. The easiest way to do this is to add an item at the end of the existing list. This is the easiest of your operation.

To add an item to the list, you first check whether the list is already full. A list is full if its count of items is equal or higher than the maximum number you had set. If the list is not empty, you can add an item at the end and increase the count by one. Here is how this can be done:

Header File: listofnumbers.h

#pragma once

const int MaxItems = 20;
//---------------------------------------------------------------------------
public __gc class CListOfNumbers
{
private:
	System::Double Item[];
	int Size;

public:
	CListOfNumbers(void);
	virtual ~CListOfNumbers(void);
	int Count(void);
	bool Add(double item);
};
//---------------------------------------------------------------------------

Source Code: listofnumbers.cpp

#include "StdAfx.h"
#include ".\listofnumbers.h"
#using <mscorlib.dll>

//---------------------------------------------------------------------------
CListOfNumbers::CListOfNumbers(void)
: Size(0)
{
	Item = new System::Double[MaxItems];
}
//---------------------------------------------------------------------------
CListOfNumbers::~CListOfNumbers(void)
{
}
//---------------------------------------------------------------------------
// Provides the current number of items in the list
int CListOfNumbers::Count(void)
{
	return Size;
}
//---------------------------------------------------------------------------
// Adds a new item to the list if the list is not full
// Increases the number of items in the list
// Returns true if the item was added, otherwise returns false
bool CListOfNumbers::Add(double item)
{
	// Make sure the list is not yet full
	if( Size < MaxItems )
	{
		// Since the list is not full, add the "item" at the end
		Item[Size] = item;
		// Increase the count and return the new position
		Size++;

		// Indicate that the item was successfully added
		return true;
	}
	// If the item was not added, return false;
	return false;
}

Once you have a means of adding items to the list, you can effectively create a list of items. Here is an example:

Source Code: Exercise.cpp

// This is the main project file for VC++ application project 
// generated using an Application Wizard.

#include "stdafx.h"
#include ".\listofnumbers.h"

#using <mscorlib.dll>

using namespace System;

int _tmain()
{
    // TODO: Please replace the sample code below with your own.
    CListOfNumbers *List = __gc new CListOfNumbers;
	
    List->Add(224.52);
    List->Add(60.48);
    List->Add(1250.64);
    List->Add(8.86);
    List->Add(1005.36);

    Console::WriteLine(S"Current Number of Items: {0}", __box(List->Count()));

    Console::WriteLine(S"");
    return 0;
}

This would produce:

Current Number of Items: 5
Press any key to continue

Item Retrieval

After adding items to a list, you can retrieve them to do what you intended the list for. To retrieve an item, you can locate an item by its position, the same way you would do for an array. Having this index, you can check if the position specified is negative or higher than the current count of items. If it is, there is nothing much to do since the index would be wrong. If the index is in the right range, you can retrieve its corresponding item. The method to do this can be implemented as follows:

Header File: listofnumbers.h

#pragma once

const int MaxItems = 20;
//---------------------------------------------------------------------------
public __gc class CListOfNumbers
{
private:
	System::Double Item[];
	int Size;

public:
	CListOfNumbers(void);
	virtual ~CListOfNumbers(void);
	int Count(void);
	bool Add(double item);
	double Retrieve(int pos);
};
//---------------------------------------------------------------------------

Source Code: listofnumbers.cpp

//---------------------------------------------------------------------------
// Retrieves an item from the list based on the specified index
double CListOfNumbers::Retrieve(int pos)
{
	// Make sure the index is in the range
	if( pos >= 0 && pos <= Size )
		return Item[pos];
	// If the index was wrong, return 0
	return 0;
}
//---------------------------------------------------------------------------

You can then call such a method to locate an item and use its value. Here is an example:

Source Code: Exercise.cpp

// This is the main project file for VC++ application project 
// generated using an Application Wizard.

#include "stdafx.h"
#include ".\listofnumbers.h"

#using <mscorlib.dll>

using namespace System;

int _tmain()
{
    // TODO: Please replace the sample code below with your own.
    CListOfNumbers *List = __gc new CListOfNumbers;
	
    List->Add(224.52);
    List->Add(60.48);
    List->Add(1250.64);
    List->Add(8.86);
    List->Add(1005.36);

    for(int i = 0; i < List->Count(); i++)
	Console::WriteLine(S"Item {0}: {1}", __box(i + 1), __box(List->Retrieve(i)));

    Console::WriteLine(S"");
    return 0;
}

This would produce:

Item 1: 224.52
Item 2: 60.48
Item 3: 1250.64
Item 4: 8.86
Item 5: 1005.36

Press any key to continue

Complex Operations on a List

Item Insertion

Inserting a new item in the list allows you to add one at a position of your choice. To insert a new item in the list, you must provide the new item and the desired position. Before performing this operation, you must first check two things. First, the list must not be empty. Second, the specified position must be in the allowed range.

The method can be implemented as follows:

Header File: listofnumbers.h

#pragma once

const int MaxItems = 20;
//---------------------------------------------------------------------------
public __gc class CListOfNumbers
{
private:
	System::Double Item[];

public:
	CListOfNumbers(void);
	virtual ~CListOfNumbers(void);
	int Size;
	int Count(void);
	bool Add(double item);
	double Retrieve(int pos);
	bool Insert(double item, int pos);
};
//---------------------------------------------------------------------------

Source Code: listofnumbers.cpp

//---------------------------------------------------------------------------
// Before performing this operation, check that
// 1. The list is not full
// 2. The specified position is in an allowable range
// Inserts a new item at a specified position in the list
// After the new item is inserted, the count is increased
bool CListOfNumbers::Insert(double item, int pos)
{
	// Check that the item can be added to the list
	if( Size < MaxItems && pos >= 0 && pos <= Size )
	{
		// Since there is room,
		// starting from the end of the list to the new position,
		// push each item to the next or up
		// to create room for the new item
		for(int i = Size; i > pos-1; i--)
			Item[i+1] = Item[i];
		// Now that we have room, put the new item in the position created
		Item[pos] = item;
		// Since we have added a new item, increase the count
		Size++;
		// Indicate that the operation was successful
		return true;
	}
	// Since the item could not be added, return false
	return false;
}
//---------------------------------------------------------------------------

Here is a test of the new method:

Source Code: Exercise.cpp

// This is the main project file for VC++ application project 
// generated using an Application Wizard.

#include "stdafx.h"
#include ".\listofnumbers.h"

#using <mscorlib.dll>

using namespace System;

int _tmain()
{
    // TODO: Please replace the sample code below with your own.
	CListOfNumbers *List = __gc new CListOfNumbers;
	
	List->Add(224.52);
	List->Add(60.48);
	List->Add(1250.64);
	List->Add(8.86);
	List->Add(1005.36);

    for(int i = 0; i < List->Count(); i++)
	Console::WriteLine(S"Item {0}: {1}", __box(i + 1), __box(List->Retrieve(i)));

    List->Insert(555.25, 2);

    for(int i = 0; i < List->Count(); i++)
	Console::Write(S"\nItem {0}: {1}", __box(i + 1), __box(List->Retrieve(i)));

    Console::WriteLine(S"\n");
    return 0;
}

This would produce:

Item 1: 224.52
Item 2: 60.48
Item 3: 1250.64
Item 4: 8.86
Item 5: 1005.36

Item 1: 224.52
Item 2: 60.48
Item 3: 555.25
Item 4: 1250.64
Item 5: 8.86
Item 6: 1005.36

Press any key to continue

Item Deletion

Another operation you can perform on a list consists of deleting an item. This is also referred to as removing the item. To delete an item from the list, you can provide its position. Before performing the operation, you can first check that the specified position is valid. The method to perform this operation can be implemented as follows:

Header File: listofnumbers.h

#pragma once

const int MaxItems = 20;
//---------------------------------------------------------------------------
public __gc class CListOfNumbers
{
private:
	System::Double Item[];

public:
	CListOfNumbers(void);
	virtual ~CListOfNumbers(void);
	int Size;
	int Count(void);
	bool Add(double item);
	double Retrieve(int pos);
	bool Insert(double item, int pos);
	bool Delete(int pos);
};
//---------------------------------------------------------------------------

Source Code: listofnumbers.cpp

#include "StdAfx.h"
#include ".\listofnumbers.h"
#using <mscorlib.dll>

//---------------------------------------------------------------------------
CListOfNumbers::CListOfNumbers(void)
: Size(0)
{
	Item = new System::Double[MaxItems];
}
//---------------------------------------------------------------------------
CListOfNumbers::~CListOfNumbers(void)
{
}
//---------------------------------------------------------------------------
// Provides the current number of items in the list
int CListOfNumbers::Count(void)
{
	return Size;
}
//---------------------------------------------------------------------------
// Adds a new item to the list if the list is not full
// Increases the number of items in the list
// Returns true if the item was added, otherwise returns false
bool CListOfNumbers::Add(double item)
{
	// Make sure the list is not yet full
	if( Size < MaxItems )
	{
		// Since the list is not full, add the "item" at the end
		Item[Size] = item;
		// Increase the count and return the new position
		Size++;

		// Indicate that the item was successfully added
		return true;
	}
	// If the item was not added, return false;
	return false;
}
//---------------------------------------------------------------------------
// Retrieves an item from the list based on the specified index
double CListOfNumbers::Retrieve(int pos)
{
	// Make sure the index is in the range
	if( pos >= 0 && pos <= Size )
		return Item[pos];
	// If the index was wrong, return 0
	return 0;
}
//---------------------------------------------------------------------------
// Before performing this operation, check that
// 1. The list is not full
// 2. The specified position is in an allowable range
// Inserts a new item at a specified position in the list
// After the new item is inserted, the count is increased
bool CListOfNumbers::Insert(double item, int pos)
{
	// Check that the item can be added to the list
	if( Size < MaxItems && pos >= 0 && pos <= Size )
	{
		// Since there is room,
		// starting from the end of the list to the new position,
		// push each item to the next or up
		// to create room for the new item
		for(int i = Size; i > pos-1; i--)
			Item[i+1] = Item[i];
		// Now that we have room, put the new item in the position created
		Item[pos] = item;
		// Since we have added a new item, increase the count
		Size++;
		// Indicate that the operation was successful
		return true;
	}
	// Since the item could not be added, return false
	return false;
}
//---------------------------------------------------------------------------
// Removes an item from the list
// First check that the specified position is valid
// Deletes the item at that position and decreases the count
bool CListOfNumbers::Delete(int pos)
{
	// Make sure the position specified is in the range
	if( pos >= 0 && pos <= Size )
	{
		// Since there is room, starting at the specified position,
		// Replace each item by the next
		for(int i = pos; i < Size; i++)
			Item[i] = Item[i+1];
		// Since an item has been  removed, decrease the count
		Size--;
		// Indicate that the operation was successful
		return true;
	}
	// Since the position was out of range, return false
	return false;
}
//---------------------------------------------------------------------------

Here is a test of the new method:

Source Code: Exercise.cpp

// This is the main project file for VC++ application project 
// generated using an Application Wizard.

#include "stdafx.h"
#include ".\listofnumbers.h"

#using <mscorlib.dll>

using namespace System;

int _tmain()
{
    // TODO: Please replace the sample code below with your own.
    CListOfNumbers *List = __gc new CListOfNumbers;
	
    List->Add(224.52);
    List->Add(60.48);
    List->Add(1250.64);
    List->Add(8.86);
    List->Add(1005.36);

    for(int i = 0; i < List->Count(); i++)
	Console::WriteLine(S"Item {0}: {1}", __box(i + 1), __box(List->Retrieve(i)));
	
    List->Delete(2);
	
    for(int i = 0; i < List->Count(); i++)
	Console::Write(S"\nItem {0}: {1}", __box(i + 1), __box(List->Retrieve(i)));

    Console::WriteLine(S"\n");
    return 0;
}

This would produce:

Item 1: 224.52
Item 2: 60.48
Item 3: 1250.64
Item 4: 8.86
Item 5: 1005.36

Item 1: 224.52
Item 2: 60.48
Item 3: 8.86
Item 4: 1005.36

Press any key to continue


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