Operations on a Collection
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Operations on a Collection |
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Adding an Item |
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The primary operation you can perform on a list is to add a new item to it, since a list is fundamentally empty when it starts. In order to indicate that you want to add an item to the list, you can create a method that receives an item as argument. For the return type, you have two main options. Because the main job of this method is to add a new item, which it hardly fails to do if you implement it right, it can be defined as void. Alternatively, you can make it return the position of the new item in the list. Here is an example: public class Numbers
{
int size;
Number Sample;
public Number Head;
public Numbers()
{
size = 0;
Head = null;
}
public int Count
{
get { return size; }
}
public int Add(Number NewItem)
{
Number Sample = new Number();
Sample = NewItem;
Sample.Next = Head;
Head = Sample;
return size++;
}
}
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Once a list exists, the user can explore it. One of the operations performed on items is to locate and retrieve one. To do this, you can create a method that takes as argument an index. The method would examine the argument with regards to the number of items in the list to make sure the argument's value is in the range of the current items of the list. If the number is too low or too high, the method can return null or 0. If the number is in the range, the method can return the item at that position. Here is an example: public class Numbers
{
int size;
Number Sample;
public Number Head;
public Numbers()
{
size = 0;
Head = null;
}
public int Count
{
get { return size; }
}
public int Add(Number NewItem)
{
Number Sample = new Number();
Sample = NewItem;
Sample.Next = Head;
Head = Sample;
return size++;
}
public Number Retrieve(int Position)
{
Number Current = Head;
for (int i = Count - 1; i > Position && Current != null; i--)
Current = Current.Next;
return Current;
}
}
Deleting an item consists of removing it from the list. There are two main approaches you can use. You can simply ask the class to delete an item. In this case, it is usually the item at the end that gets deleted. If you do this, make sure you perform other routines operations such as decrementing the count of items in the list. Here is an example: public class Numbers
{
. . . No Change
public bool Delete()
{
if (Head == null)
{
Console.WriteLine("The list is empty");
return false;
}
Number Current;
Current = Head.Next;
Head.Next = Current.Next;
size--;
return true;
}
}
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Another technique used to delete an item consists of specifying the position of the item to be deleted. To do this, you can pass an argument as the desired position. The method would check the range of values of the current list. If the specified position is beyond the appropriate range, the method can return false, 0, or null, depending on how you create it. |
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using System;
namespace FlowerShop4
{
public abstract class AFlower
{
protected int items;
public AFlower()
{
items = 0;
}
public int Count
{
get { return items; }
}
public abstract int Add(Flower obj);
public abstract Flower Get(int index);
public abstract bool Delete();
}
public class FlowerInventory : AFlower
{
public Flower Head;
public Flower Inventory;
public FlowerInventory()
{
Head = null;
}
public override int Add(Flower NewFlower)
{
Flower Sample = new Flower();
Sample = NewFlower;
Sample.Next = Head;
Head = Sample;
return items++;
}
public override Flower Get(int index)
{
Flower Current = Head;
for(int i = Count - 1;
i > index && Current != null;
i--)
Current = Current.Next;
return Current;
}
public override bool Delete()
{
if (Head == null)
{
Console.WriteLine("The inventory is empty");
return false;
}
Flower Current;
Current = Head.Next;
Head.Next = Current.Next;
items--;
return true;
}
}
}
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using System;
namespace FlowerShop4
{
public class Program
{
static int Main(string[] args)
{
FlowerInventory flowers = new FlowerInventory();
Flower nice;
nice = new Flower();
nice.Type = FlowerType.Lilies;
nice.Color = FlowerColor.White;
nice.Arrangement = FlowerArrangement.Bouquet;
nice.UnitPrice = 39.95M;
flowers.Add(nice);
nice = new Flower();
nice.Type = FlowerType.Daisies;
nice.Color = FlowerColor.Mixed;
nice.Arrangement = FlowerArrangement.Bouquet;
nice.UnitPrice = 40.50M;
flowers.Add(nice);
nice = new Flower();
nice.Type = FlowerType.Carnations;
nice.Color = FlowerColor.Lavender;
nice.Arrangement = FlowerArrangement.Any;
nice.UnitPrice = 34.85M;
flowers.Add(nice);
nice = new Flower();
nice.Type = FlowerType.Roses;
nice.Color = FlowerColor.Pink;
nice.Arrangement = FlowerArrangement.Bouquet;
nice.UnitPrice = 29.95M;
flowers.Add(nice);
nice = new Flower();
nice.Type = FlowerType.Daisies;
nice.Color = FlowerColor.Yellow;
nice.Arrangement = FlowerArrangement.Vase;
nice.UnitPrice = 42.75M;
flowers.Add(nice);
Console.WriteLine("//=//=//=//=//=//=//=//=//=//=//=//=//=//=//");
Console.WriteLine("Total: {0} flower items in current inventory",
flowers.Count);
Console.WriteLine("--------------------------------------------");
Console.WriteLine("Inventory Summary");
for (int i = 0; i < flowers.Count; i++)
{
Console.WriteLine("------------------------");
Console.WriteLine("Flower Information");
Console.WriteLine("Type: {0}",
flowers.Get(i).Type);
Console.WriteLine("Color: {0}",
flowers.Get(i).Color);
Console.WriteLine("Arrangement: {0}",
flowers.Get(i).Arrangement);
Console.WriteLine("Unit Price: {0:F}",
flowers.Get(i).UnitPrice);
}
Console.WriteLine("//=//=//=//=//=//=//=//=//=//=//=//=//=//=//");
flowers.Delete();
flowers.Delete();
Console.WriteLine("//=//=//=//=//=//=//=//=//=//=//=//=//=//=//");
Console.WriteLine("Total: {0} flower items in current inventory",
flowers.Count);
Console.WriteLine("--------------------------------------------");
Console.WriteLine("Inventory Summary");
for (int i = 0; i < flowers.Count; i++)
{
Console.WriteLine("------------------------");
Console.WriteLine("Flower Information");
Console.WriteLine("Type: {0}",
flowers.Get(i).Type);
Console.WriteLine("Color: {0}",
flowers.Get(i).Color);
Console.WriteLine("Arrangement: {0}",
flowers.Get(i).Arrangement);
Console.WriteLine("Unit Price: {0:F}",
flowers.Get(i).UnitPrice);
}
Console.WriteLine("//=//=//=//=//=//=//=//=//=//=//=//=//=//=//");
return 0;
}
}
}
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//=//=//=//=//=//=//=//=//=//=//=//=//=//=// Total: 5 flower items in current inventory -------------------------------------------- Inventory Summary ------------------------ Flower Information Type: Lilies Color: White Arrangement: Bouquet Unit Price: 39.95 ------------------------ Flower Information Type: Daisies Color: Mixed Arrangement: Bouquet Unit Price: 40.50 ------------------------ Flower Information Type: Carnations Color: Lavender Arrangement: Any Unit Price: 34.85 ------------------------ Flower Information Type: Roses Color: Pink Arrangement: Bouquet Unit Price: 29.95 ------------------------ Flower Information Type: Daisies Color: Yellow Arrangement: Vase Unit Price: 42.75 //=//=//=//=//=//=//=//=//=//=//=//=//=//=// //=//=//=//=//=//=//=//=//=//=//=//=//=//=// Total: 3 flower items in current inventory -------------------------------------------- Inventory Summary ------------------------ Flower Information Type: Lilies Color: White Arrangement: Bouquet Unit Price: 39.95 ------------------------ Flower Information Type: Daisies Color: Mixed Arrangement: Bouquet Unit Price: 40.50 ------------------------ Flower Information Type: Daisies Color: Yellow Arrangement: Vase Unit Price: 42.75 //=//=//=//=//=//=//=//=//=//=//=//=//=//=// Press any key to continue . . . |
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Locating an Item |
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One of the operations hardly performed on a list is to find an item. This is because if you ask a list to locate a particular item, you must provide as much information as possible. Probably the most expedient way you can do this is to completely define an item and pass it to the list. Only if the item is found in the list would it be recognized. Here is an example: |
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Practical
Learning: Adding Items to a Collection
using System;
public class Number
{
public double Item;
public Number Next;
}
public class Numbers
{
int size;
Number Sample;
public Number Head;
public Numbers()
{
size = 0;
Head = null;
}
public int Count
{
get { return size; }
}
public int Add(Number NewItem)
{
Number Sample = new Number();
Sample = NewItem;
Sample.Next = Head;
Head = Sample;
return size++;
}
public Number Retrieve(int Position)
{
Number Current = Head;
for (int i = Count - 1; i > Position && Current != null; i--)
Current = Current.Next;
return Current;
}
public bool Delete()
{
if (Head == null)
{
Console.WriteLine("The list is empty");
return false;
}
Number Current;
Current = Head.Next;
Head.Next = Current.Next;
size--;
return true;
}
public bool Find(Number toFind)
{
Number Current = new Number();
if (toFind == null)
return false;
for (Current = Head; Current != null; Current = Current.Next)
{
if( Current.Item == toFind.Item )
return true;
}
return false;
}
}
public class Program
{
static int Main(string[] args)
{
Number real;
Numbers reals = new Numbers();
real = new Number();
real.Item = 2974.03;
reals.Add(real);
real = new Number();
real.Item = 748.25;
reals.Add(real);
real = new Number();
real.Item = 50883.82;
reals.Add(real);
real = new Number();
real.Item = 29.24;
reals.Add(real);
real = new Number();
real.Item = 772.85;
reals.Add(real);
real = new Number();
real.Item = 106628.06;
reals.Add(real);
Console.WriteLine("Number of items: {0}", reals.Count);
for (int i = 0; i < reals.Count; i++)
{
Number nbr = reals.Retrieve(i);
Console.WriteLine("Number[{0}] = {1}", i, nbr.Item);
}
reals.Delete();
Console.WriteLine("\nNumber of items: {0}", reals.Count);
for (int i = 0; i < reals.Count; i++)
{
Number nbr = reals.Retrieve(i);
Console.WriteLine("Number[{0}] = {1}", i, nbr.Item);
}
Number nbrToFind = new Number();
nbrToFind.Item = 26486.56;
bool Found = reals.Find(nbrToFind);
if (Found == true)
Console.WriteLine("\nThe number {0} was found in the list", nbrToFind.Item);
else
Console.WriteLine("\nThe number {0} was NOT found in the list", nbrToFind.Item);
nbrToFind = new Number();
nbrToFind.Item = 50883.82;
Found = reals.Find(nbrToFind);
if (Found == true)
Console.WriteLine("The number {0} was found in the list\n", nbrToFind.Item);
else
Console.WriteLine("The number {0} was NOT found in the list\n", nbrToFind.Item);
return 0;
}
}
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This would produce: Number of items: 6 Number[0] = 2974.03 Number[1] = 748.25 Number[2] = 50883.82 Number[3] = 29.24 Number[4] = 772.85 Number[5] = 106628.06 Number of items: 5 Number[0] = 2974.03 Number[1] = 748.25 Number[2] = 50883.82 Number[3] = 29.24 Number[4] = 106628.06 The number 26486.56 was NOT found in the list The number 50883.82 was found in the list Press any key to continue . . .
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